AN ANALYSIS OF A SONORAN DESERT SPECIES DIVERSITY GRADIENT
Item Type text; Dissertation-Reproduction (electronic)
Authors Yensen, Arthur Eric, 1944-
Publisher The University of Arizona.
Rights Copyright © is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author.
Download date 24/09/2021 16:14:26
Link to Item http://hdl.handle.net/10150/288134 INFORMATION TO USERS
This material was produced from a microfilm copy of the original document. While the most advanced technological means to photograph and reproduce this document have been used, the quality is heavily dependent upon the quality of the original submitted.
The following explanation of techniques is provided to help you understand markings or patterns which may appear on this reproduction.
1.The sign or "target" for pages apparently lacking from the document photographed is "Missing Page(s)". If it was possible to obtain the missing page(s) or section, they are spliced into the film along with adjacent pages. This may have necessitated cutting thru an image and duplicating adjacent pages to insure you complete continuity.
2. When an image on the film is obliterated with a large round black mark, it is an indication that the photographer suspected that the copy may have moved during exposure and thus cause a blurred image. You will find a good image of the page in the adjacent frame.
3. When a map, drawing or chart, etc., was part of the material being photographed the photographer followed a definite method in "sectioning" the material. It is customary to begin photoing at the upper left hand corner of a large sheet and to continue photoing from left to right in equal sections with a small overlap. If necessary, sectioning is continued again — beginning below the first row and continuing on until complete.
4. The majority of users indicate that the textual content is of greatest value, however, a somewhat higher quality reproduction could be made from "photographs" if essential to the understanding of the dissertation. Silver prints of "photographs" may be ordered at additional charge by writing the Order Department, giving the catalog number, title, author and specific pages you wish reproduced.
5. PLEASE NOTE: Some pages may have indistinct print. Filmed as received.
Xerox University Microfilms 300 North Zeeb Road Ann Arbor, Michigan 48106 I I 74-4184
YENSEN, Arthur Eric, 1944- AN ANALYSIS OF A SONORAN DESERT SPECIES DIVERSITY GRADIENT.
The University of Arizona, Ph.D., 1973 Biology
University Microfilms, A XEROXCompany , Ann Arbor, Michigan
THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED. AN ANALYSIS OF A SONORAN DESERT SPECIES
DIVERSITY GRADIENT
by
Arthur Eric Yensen
A Dissertation Submitted to the Faculty of the
DEPARTMENT OF BIOLOGICAL SCIENCES
In Partial Fulfillment of the Requirements For the Degree of
DOCTOR OF PHILOSOPHY WITH A MAJOR IN ZOOLOGY
In the Graduate College
THE UNIVERSITY OF ARIZONA
19 7 3 THE UNIVERSITY OF ARIZONA
GRADUATE COLLEGE
I hereby recommend that this dissertation prepared under my direction by Arthur Erio Yenaen entitled AN ANALYSIS OF A SONORAN DESERT
SPECIES DIVERSITY GRADIENT be accepted as fulfilling the dissertation requirement of the degree of DOCTOR OF PHILOSOPHY
lu • CLl.I% 'ait I (97 5 Dissertation Director Date
After inspection of the final copy of the dissertation, the following members of the Final Examination Committee concur in its approval and recommend its acceptance:
^,tf 73
~X CXjo. I If ?i>
^ J Q-U.rj I'f 7-?
, C? t 1 %
JCo~V\ C-AsSl v uXJL<-^ Qo y-, 7, V / /) 7 3
This approval and acceptance is contingent on the candidate's adequate performance and defense of this dissertation at the final oral examination. The inclusion of this sheet bound into the library copy of the dissertation is evidence of satisfactory performance at the final examination. STATEMENT BY AUTHOR
This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the Uni versity Library to be made available to borrowers under rules of the Library.
Brief quotations from this dissertation are allow able without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manu script in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.
SIGNED; ACKNOWLEDGMENTS
This study was facilitated by help from several sources which I am happy to acknowledge here. I wish to thank the National Park Service for granting permission to set up a study site (site 4) inside the boundary of
Saguaro National Monument. I also wish to thank Dr. E. L.
Cockrura for the extended loan of the mammal traps, Mr. R. R.
Snelling of the Los Angeles County .Museum for checking my ant identifications, and my brother, N. P. Yensen, for assisting in the field with some of the foliage height diversity measurements. Drs. S. M. Russell, H. R. Pulliam,
C. H. Lowe, D. A. Thomson, C. T. Mason, and R. W. Hoshaw read and offered constructive criticism of this manuscript.
I have especially appreciated their advice and encourage ment during the course of this study. I have profited from valuable discussion of species diversity with Dr. Pulliam and Dr. J. R. Hastings. My wife, Dana, assisted with various portions of the field work and offered excellent suggestions for improving the manuscript.
iii TABLE OF CONTENTS
Page
LIST OF TABLES vi
LIST OF ILLUSTRATIONS vii
ABSTRACT ix
INTRODUCTION 1
The Measurement of Diversity 2 Explanations of Diversity 21
THE STUDY AREA 27
The Tucson Mountains 27 The Study Sites 30
METHODS 33
THE DIVERSITY PATTERNS 40
DISCUSSION 69
SUMMARY AND CONCLUSIONS 80
APPENDIX Is FORMULAE OF SPECIES DIVERSITY INDICES AS USED BY THE ORIGINAL AUTHORS, SHOWING MODIFICATIONS MADE IN THIS PAPER IN THE INTEREST OF CONSISTENT USE OF SYMBOLS 83
APPENDIX II: RESULTS OF BIRD CENSUSES AT THE FIVE STUDY SITES BY MONTHS 86
APPENDIX III; RESULTS OF RODENT TRAPPING 95
APPENDIX IV; RESULTS OF LIZARD CENSUSES EXPRESSED AS INDIVIDUALS PER HECTARE 97
APPENDIX V: NUMBER OF ANT COLONIES (1.6 HA. TRANSECT) AT EACH SITE 98
iv V
TABLE OF CONTENTS (Continued)
Page
APPENDIX VI; FOLIAGE ARTHROPOD SAMPLING RESULTS, SEPTEMBER 1972, BASED ON 1000 SWEEPS AT EACH SITE 100
APPENDIX VII: PERENNIAL PLANTS: NUMBER OF INDIVIDUALS FOUND ON TEN 0.1 HECTARE QUADRATS Ill
APPENDIX VIII: LIFE FORMS OF PERENNIAL PLANT SPECIES USED IN CALCULATING PCD VALUES 113
APPENDIX IX: NUMBERS OF ANNUALS FROM 50 ONE- METER SQUARE QUADRATS AT EACH SITE 115
LITERATURE CITED 117 LIST OF TABLES
Table Page
1. Effect of the evenness component on the value of the diversity index 13
2. Effect of the richness component on the value of the index 16
3. Effect of increasing numbers of individuals (N) and species (S) on the value of the index 17
4. Location of study sites 31
5. Number of individuals (number of pairs x 2) of breeding birds at the five study sites on the Tucson Mountains bajada, spring and summer, 1972 41
6. Seasonal changes in bird species diversity (H') values at the five study sites 47
7. Diversity values (H') of the major com munity components studied at the five study sites 50
8. Perennial plants: canopy cover as a percentage of one kilometer of line intercept at each site 57
9. Spring and summer annual plant numbers, species, and bioroass per 50 one-meter square quadrats at each site 60
10. Foliage height diversity (Hl) using various permutations of layers 62
11. Physiognomic cover diversity (PCD) values obtained using four and ten categories of growth forms and species cover diversity (SCD) values 62
vi LIST OF ILLUSTRATIONS
Figure Page
1. Examples of species-area curves 5
2. Example of a species abundance curve 7
3. Comparison of H' and Dg 20
4. Map of study site 32
5. Vertebrate populations 43
6. Number of species at each site 44
7. Species diversity (H1) of breeding birds, rodents, ants, and foliage arthropods .... 45
8. Species diversity (H") of lizards, perennial plants, spring annuals, and summer annual plants .... 46
9. Seasonal variation in bird species diversity (H1) at the five study sites during 1972 48
10. Relationship between rodent and lizard diversity patterns and bur-sage CFranseria deltoidea) density 52
11. Arthropod populations 53
12. Plant populations 55
13. Perennial plant coverage 56
14. Regression of bird species diversity (BSD) on physiognomic cover diversity (PCD-four categories) 64
15. Regression of bird species diversity (BSD) on physiognomic cover diversity lPCD-10 categories) 65
vii viii
LIST OF ILLUSTRATIONS (Continued)
Figure Page
16. Regression of bird species diversity (BSD) on plant species cover diversity CSCD) 66
17. Regression of bird species richness on number of plant species 67
18. Regression of bird species diversity (H') on number of plant species 68 ABSTRACT
Ten species diversity indices were discussed and compared using hypothetical and actual species abundance distributions. Only two indices, H' and D , consistently b increased with increases in richness and evenness. Since
H' has been widely used, it was adopted in order to facili tate comparisons to other studies. H1 values for birds, rodents, lizards, ants, foliage arthropods, perennial plants, spring annual plants, and summer annual plants were determined at five study sites on a complex environmental gradient in the Tucson Mountains, Arizona. The eight groups of organisms exhibited six different diversity patterns along the gradient, indicating that the diversity of one community relative to other communities cannot be judged from a single group of organisms. A reciprocal relationship, termed "consumer trade-off," was observed between lizards and rodents and between ants and foliage arthropods. When the diversity of one member of the pair increased, the other decreased. MacArthur's foliage height diversity model failed to predict bird species diversity, whereas models based on the diversity of coverage of plant physiognomic growth forms were highly correlated with bird species diversity. The number of plant species was also
ix X highly correlated with the number of bird species and bird species diversity. Bird species diversity fluctuated less, seasonally, in more complex habitats. INTRODUCTION
The study of species diversity began with the common observation that some biological communities contain more species than others. Despite the simplicity of this ob servation, its explanation, the means of measuring it, and its significance have been the subjects of a sizable body of literature. And despite the extent of this literature, a general theory of species diversity has not emerged. As
Eberhardt (1971:359) has stated, "[Species diversity is]
, . , one of the more disorganized areas of ecology."
Any adequate explanation of species diversity must also have the power of predicting what species diversity will be under given conditions. The current explanations of species diversity have the status of hypotheses; ex perimentation with predictive models has just begun. In addition, any adequate explanation of species diversity should also help relate diversity to other aspects of community organization. Are more diverse communities more stable than less diverse communities as is widely believed?
Is diversity equivalent to community organization as
Margalef (1958) has suggested?
The present study was undertaken as a step toward understanding the role of species diversity in community
1 2 organization. Since species diversity studies in the past have invariably dealt with only a single group of organisms
(e,g., birds), it seemed desirable to make the neglected comparisons between the major components of the community to learn if the species diversities of major groups of organisms are correlated. If they are, building predictive models of community diversity would be greatly simplified.
It was realized that a community approach would limit the number of sites which could be compared, but it might also yield new insights into the diversity problem. The com munity approach was therefore adopted. Consequently, species diversity values for birds, rodents, lizards, ants, foliage arthropods, perennial plants, and spring and summer annuals were determined for five study sites located along a vegetational gradient in the Tucson Mountains, Pima County,
Arizona. Using this data, two predictive models of bird species diversity (BSD) were tested and an attempt was made to determine if there was less seasonal fluctuation in BSD in more diverse habitats. Also, most of the numerous species diversity indices which have been proposed in the literature were evaluated as a part of this study.
The Measurement of Diversity
One result of the voluminous diversity literature has been that several meanings have been given to the term
"diversity," Diversity (or species diversity) can refer 3 simply to the number of species in a given area. This was the original meaning, and the term is still used in this
sense. This aspect of diversity has been termed "richness"
by Tramer (1969) or "alpha diversity" by Whittaker (1960).
The number of species per unit area has been termed "den
sity" (Simpson, 1964). However, since in a community some
species are much more abundant than others, many persons
have felt that some sort of diversity measure should be
devised which would take into account relative species
abundances. To use JMacArthur's example (MacArthur and
MacArthur, 1961), a two-species community with 50 indi
viduals of one species and 50 individuals of the second
seems more diverse than a community with 99 individuals
of one species and one individual of the second. The
relative abundance of each species in the community as
compared to the other species is referred to as the
"evenness" component of species diversity. In the example
above, the species in the first community are more evenly
distributed than in the second. However, according to
Lloyd and Ghelardi (1964), the two components of diversity
are richness and "equitability" rather than evenness, since
"numerical equality among species is too much to expect"
(p. 217). Equitability then refers to how closely a
species abundance distribution approximates MacArthur's
(1957) "broken stick" model of species abundances. However, 4 some authors Ce.g., Trainer, 1969) use the terms "evenness" and "equitability" interchangably in reference to numerical equality of species.
A diversity index is a means of combining richness and evenness into a single expression. Various diversity indices have been proposed (Fisher, Corbet and Williams,
1943; Simpson, 1949; MacArthur, 1955, 1957, 1972; Margalef,
1957, 1958; Odum, Cantlon and Kornicker, 1960; Mcintosh,
1967; Hurlbert, 1971; Fager, 1972; and others). Before the results of this study could be completed, it was first necessary to select the most suitable index from those proposed. Therefore, an attempt was made to understand how each index works and then the indices were compared using both hypothetical and actual species distributions. The approach taken is of necessity that of a biologist rather than a mathematician.
The first approaches to diversity indices were based on species-area (Fig. 1) and species abundance rela tionships. Gleason (1922) plotted cumulative species versus the logarithm of the area sampled. This yielded a straight line on a semi-logarithmic plot. If the rela tionship between species and area is constant, the ratio is a type of index. Yount (1956, see also Odum, et al.,
1960) plotted cumulative species versus the logarithm of AS individuals in the form, ^jiogN1"' wIlere s the number of 5
30 *
20 "
10 CO d) "H O d) & w o u 0.2 0.4 0.6 0.8 1.0
10 0.2 0.4 0.6 1.0 Area (hectares)
Figure 1. Examples of species-area curves. — Data from site 4 perennial plant sampling plotted arith metically (above) and semi-logarithmically (below). Lines represent idealized curves. 6 species and N is the total number of individuals in the sample. This ratio is also a type of diversity index.
Another form of this index is Margalef's (1958) form,
If the number of individuals of each species is plotted on the ordinate and the species in order of abun dance on the abscissa, the resulting curve is an example of a species abundance curve (Fig. 2). "The regularity with which the numbers of individuals declines from the most abundant to the rare species has suggested that the relation
ship might be simple mathematically or might reflect some
aspect of community order," as Hairston (1964:230) has suc
cinctly expressed it. The species abundance curves used by
Fisher, Corbet and Williams (1943) approximated a negative
binomial distribution. They reasoned that since the pattern
of species abundances approximates a negative binomial dis
tribution, one has only to supply the number of individuals
and the number of species and the diversity is given by a,
a parameter of the log series. (This diversity index,
alpha, should not be confused with Whittaker's alpha di
versity.) Unfortunately, many species abundance curves do
not fit a negative binomial distribution but approximate a
lognormal or other distribution pattern (cf. Preston,
1948; Hairston, 1959; Whittaker, 1965).
The most widely used measure is from information
theory (Shannon and Weaver, 1949, based on the pioneering 50
40
30
20
x *
X * 10
X*
—n 10 20 30 40 50 60 70 80 Species Ranked in Order of Decreasing Abundance
Figure 2. Example of a species abundance curve. >— Data points from site 2 foliage arthropod samples. 8 work of Wiener) and was introduced to the ecological literature by .MacArthur (1955) and .Margalef (1957, 1958).
The form used by MacArthur, H' = ln is appropriate when working with samples, whereas Margalef's form (from 1 N1 Brillouin, 1956) f H = rr log -—t —r, is appropriate jn 1 * 2 * * * * • when the entire population is known (Pielou, 1966b). In these formulae, n^ is the number of individuals of the ith species, p^ is the proportion of the total individuals which belong to the ith species, and In is the natural or
Naperian logarithm (other bases may be used with appropriate conversion factors). Other symbols are as previously defined. (See Appendix I for a list of indices and symbols,) The information theory measure is based on the uncertainty of predicting the identity of the next species encountered, which is greater in richer, more even (or equitable) communities. Because of the logarithmic term, the relative magnitude of a species1 contribution to the value of the index steadily decreases. Therefore, many rare species in equal numbers will maximize each individual species' contribution to the value of the index and thus
yield the highest diversity value. In a sample with fewer species, the proportion of each species will be relatively greater, and because of the logarithmic term, its relative contribution to the value of the index will be less, and the H< value will be lower. Thus the more species there
are in a community and the more even their abundances, the 9
greater will be each species' relative contribution to the total diversity (H'). The measure has been criticized as being insensitive to rare species (Sager and Hasler,
1969; Hurlbert, 1971). This criticism is invalid since, as explained above, it is actually more sensitive to rare species because of the logarithmic term. It has also been criticized as being dependent on sample size because of the species-area relationship (Fig. 11. If areas of unequal sizes are compared, the larger area should have a greater number of species (other things being equal), but because species are added at a decreasing rate with increasing area, the difference in richness between areas will not be directly proportional to area and therefore difficult to compensate for when comparing diversity values, Sanders
(1968) has devised a method for comparing samples of dif
ferent sizes (see also Fager, 1972, for a criticism of this method), The simplest solution is to compare samples of
equivalent size. Margalef (1958) emphasized that the
information content (or uncertainty) of a community is a measure of its organization, although this idea has been
questioned by Hurlbert (1971). What does a given H' say
biologically about a community? MacArthur converted H'
to its antilog to get what he called the number of equally
common species, or the number of species which could be
equally common at that H'. It can also be thought of as the 10
uncertainty in accurately predicting the species of the
next individual encountered in a community (or taxonomic
segment of a community). Thus the more diverse the com munity, the greater the difficulty of guessing the identity
of the next species encountered (see Klopfer, 1969, for an
intuitive derivation of the information theory measure).
The information theory measure is widely used but difficult mathematically; Pielou has written a series of papers
(Pielou, 1966a, 1966b, 1966c) on the correct use of this measure, and Hutcheson (1970) has devised a t-test for com
paring H's. Bowman, et al. (1971), and discussions at the
end of the paper by L. L. Eberhardt and E, C. Pielou, deal
with some of the mathematical problems of this measure,
Eberhardt suggests that in light of the failure of informa
tion theory in engineering (see Gilbert, 1966) adopting a
simpler measure, such as Simpson's index, might be preferable
to struggling with the mathematics of a particularly diffi
cult measure.
Simpson's (1949) index is a measure of the concen
tration, or number of individuals belonging to a single
group. His A is the probability that two individuals
chosen randomly belong to the same species. The expres- En.^-1) sion, I = N r is an estimator of A, As n^ increases,
since it is multiplied by n^-1, the value of the numerator
increases, and hence the value of the index. The value of 11
5, thus increases as individuals are concentrated into fewer groups; or restated, i increases as diversity decreases.
This simple index has appeared in several forms. Whittaker n. 2 restated this index in the form c = E (jp-) (see Appendix
I). Levins (1966) used this formula in the form 1— = Ep. 2, D 1 as a measure of niche breadth, where B = niche breadth,
MacArthur and Wilson (1967; MacArthur, 1972) use the form
= ^V • By taking the reciprocal, the value of the s ^Pi^ index increases with diversity. This index is easy to calculate and more easily understood intuitively than the j information theory measure. In the D form, if the sample s consists of two species with equal numbers of individuals,
Dg is equal to two. If the sample consists of ten species with equal numbers of individuals, Dg is equal to ten, and
so on. Dg is thus a direct measure of the number of equally common species. Samples ordinarily do not have equal
species abundances, so D is then simply a comparative s number, with the number of equally common species being a
reference point.
A different type of diversity index was proposed
by Mcintosh (1967). The dissimilarity, or distance, between 2 two stands, j and h, is given by = J E (n^j - n^h) ,
where n^j is the value of the ith species in stand j and
n^ is the value of the ith species in stand h. A single
community could be thought of as a point with its location 2 given by d = /ZnT . This is the distance from the com munity in question to a "no-species" community, or simply to distance of the community from the origin of a co ordinate system with as many axes as species. However, since it is the number of individuals of a species that is being squared rather than the proportions, it is possible for an uneven distribution to have a higher diversity than an even distribution with the same number of individuals and species (Table 1).
A more recent index is "based on the number of
'moves' that would have to be made to convert an observed distribution of individuals among species into an even distribution" (Fager, 1972:299). The number of moves is given by NM = N — ER.n., where R. is the rank of « JL species i^. As evenness increases, fewer "moves" are required. The species are arranged in decreasing order of abundance. Ranking in increasing order will work but the signs must be reversed.
Hurlbert (1971) after decrying the plethora of diversity indices and the various meanings given the term diversity, takes the extreme view that diversity has become a "non-concept" and should be abandoned. He suggests that
"alternate species composition parameters" should be ex plored, especially the probability of interspecific en counter (PIE). PIE (A^) can be interpreted as the 13
Table 1. Effect of the evenness component on the value of the diversity index. — Numbers of individuals (N) and species (S) were held constant and equitability (J') varied using five hypothetical species-abundance distributions, each with 24 individuals and six species. See text for dis cussion of indices and Appendix I for list of symbols.
Distribution Index 1 2 3 4 5
S 6 6 6 6 6
N 24 24 24 24 24
J' 1.000 .966 .932 .886 .472
H' 1.800 1.739 1.678 1.594 .850
D 5.952 5.405 4.955 4.219 1.570 S 1 .130 .149 .185 .203 .620
.868 .850 .832 .796 .379 A1 d 1.570 1.570 1.570 1.570 1.570 a 2.568 2.568 2.568 2.568 2.568
Mcl 9.80 10.3 10.8 11.66 19.13
NM 0 13 18 25 45
The number of individuals per species in each dis tribution is as follows: Distribution 1: 4, 4, 4, 4, 4, 4. Distribution 2: 2, 3r 4, 4, 5, 6. Distribution 3: 1, 3, 4, 4, 5, 7. Distribution 4: 1, 2, 3, 4, 5, 9. Distribution 5: 1, 1, 1, 1, 1, 19. 14 probability that two individuals encountered at random will n. N-n. be of different species. PIE is given by A-^ = ( N_j^) = N 2 (1-Ep^ ). However, as Hurlbert points out, "when the first individual encountered risks being the subject of the second encounter also, as in nonlethal encounters, this probability is simply ^ = 1-^P^ 2 / the complement of
Simpson's (.1949) 'measure of concentration1" and "when it is possible to take a truly random sample of individuals from a community or other collection, the sample estimators of A^ and are provided by Simpson (1949)" (.pp. 579-580).
Thus PIE is (1) related mathematically to Simpson's index,
(2) is basically measuring the same thing as Simpson's index, and (3) is still a diversity index, despite his elaborate rephrasing. PIE increases with species richness and equitability, and can thus be used to compare the diversities of different communities.
It is sometimes instructive to calculate the evenness component of diversity. This can be done by cal culating J' (Tramer, 1969), where J' = If H* is the diversity of a sample and H'max is the maximum diversity possible with that number of species, then J' represents the evenness of the sample. As H' approaches
H'max, J' approaches 1.0. The values for other diversity indices could also be used, for example J1 = D /D_max. s s Evenness is the inverse of Whittaker's (1965) dominance concentration. See Lloyd and Ghelardi (1964) for the method of calculating equitability (e).
The diversity indices discussed above were compared first by using two series of hypothetical species abundance distributions, In the first series, numbers of individuals and species richness were held constant while evenness was varied, to test the response of each index to evenness
(Table 1). In the second series, evenness and numbers of individuals were held constant, and species richness was varied (Table 2). The indices were then compared using actual species abundance distributions (of breeding birds from Table 5, see p. 41) from a series of increasingly complex habitats where richness and numbers of individuals
steadily increased from one habitat to the next, to see
how each index responded to more normal species abundance
distributions (Table 3).
If the function of a diversity index is to combine
richness and evenness into a single expression, then the
value of an index should (1) increase proportionally with
increases in evenness, (2) increase proportionally with
increases in richness, and (3) increase with combined
increases in richness and evenness. An index which is
inconsistently responsive to one or the other or both
components would be of limited utility. If an index re
sponds only to richness, then it is difficult to see how 16
Table 2. Effect of the richness component on the value of the index. — Numbers of individuals (N) and evenness (J1) held constant and number of species (S) varied using five hypothetical species-abundance distributions, each with 24 incificuals and maximum evenness.
Distribution3 Index 1 2 3 4 5
S 24 12 6 3 1
N 24 24 24 24 24
J' 1.0 1.0 1.0 1.0 1.0
H< 3.192 2.484 1.794 1.098 0
D 24.0 12.0 6.0 3.0 1.0 s 1 0 .044 .129 .306 1.000
.999 .956 .869 .696 0 A1 d 7.23 3.46 1.57 .63 0 a 24?b 9.5b 2.57 -1.105 -4.744
Mcl 4.90 6.93 9.80 13.86 24.00
NM 0 0 0 0 0
aThe number of individuals per species in each dis tribution is as follows Distribution 1 24 species with one individual each. Distribution 2 12 species with two individuals each. Distribution 3 6 species with four individuals each. Distribution 4 3 species with eight individuals each. Distribution 5 1 species with 24 individuals.
^Estimated values extrapolated from Table 9 of Fisher, Corbet, and Williams (1943). 17
Table 3. Effect of Increasing numbers of individuals (N) and species (S) on the value of the index. — Five actual species~abundance distributions were used. Data from Table 5.
Distribution Index 1 2 3 4 5
N 5 24 39 55 73
S 3 10 15 18 21
J' .97 .95 .93 .89 .89
H' 1.056 2.189 2.593 2.572 2.739
2.78 7.69 11.76 10.53 11.49 Ds 1 .200 .091 .070 .086 .061
.800 .909 .943 .918 .928 A1 d 1.242 2.830 4.098 4.239 4.662
a 2.8 a 6.46a 8.924 9.317 9.869
.Mcl 3.00 8.62 11.18 13.82 21.33
MM 1 15 107 214 327
a Estimated, 18 the index would be an improvement over a simple species count. An index which is responsive only to evenness would be more useful, but would be better termed an "evenness index." Therefore, the response to both evenness and rich ness should be proportional, consistent, and in a positive direction for convenience. The results of testing condi tion one are presented in Table 1, the results of testing condition two are presented in Table 2, and the results of testing condition three are presented in Table 3. Some of the distributions used in Tables 1 and 2 are not likely to be encountered in nature, but are nevertheless useful in demonstrating the weaknesses of some of the indices tested.
Alpha diversity (a) and Margalef's d are not sensi tive to changes in evenness, since they are based on log series and assume that the ratio of N to S will be constant.
Although species abundance curves and species-area curves usually approximate those shown in Figures 1 and 2, they may not always do so. In case they do not, the results are apt to be misleading (Table 1). Since criterion one is not satisfied, these indices will not be considered further.
Fager's index (NM) conversely, does not respond to richness, per se, but to increases in unevenness Cor number of moves required to achieve an even distribution). • 19
Since increasing the number of species would often result in requiring more "moves", the index works in many, but not all, cases.
Mcintosh's index also gives inconsistent results.
Normally (Table 3) it increases with richness and equita- bility, but not always (Tables 1 and 2), Apparently the similarity in species composition between two communities and the diversity of the two communities are different concepts and cannot be represented by the same mathematical formulation.
Hurlbert's index, A^, responds correctly in the examples given, but the magnitude of the response, es pecially to the richness component, is low. As richness and evenness increases, the response of the index becomes proportionately smaller.
Simpson's index, 1, has the disadvantage of de creasing in value as diversity increases. For this reason,
MacArthur's modification, Ds , is preferred. Since Ds and H' respond correctly in these (and other) examples to the criteria listed above, the choice of an index is between them. Using data from the hypothetical species abundance distributions, breeding bird, and foliage insect data, D and H' were compared (Figure 3). There is a close, slightly curvilinear correspondence between the
1 two indices. Since the choice of H or D„s would not 20
*.
1.0 2.0 3.0 4.0 H'
Figure 3. Comparison of H* and Dg. — Points from Tables 1 and 2, breeding bird data, and foliage arthropod data. 21 greatly alter the results of this study, it was decided to use H' in the remainder of this paper. H" is better known and widely used, therefore the results would be more com parable to other studies.
Explanations of Diversity
Whittaker (1960) proposed the term beta diversity for the degree of change in community species composition along a vegetational gradient. On a gradient, any two given points may have some species in common. The further the points are apart, the fewer species they will have in common and the higher beta diversity will be. Beta diversity may be measured in several ways. Distance measures, such as the coefficient of community, are commonly used (Whittaker,
1970). Beta, like alpha, diversity is usually expressed as species numbers rather than as species abundance in the communities compared. Alpha and beta diversities are similar to MacArthur's (1965) between- and within-habitat diversities. Within-habitat diversity is simply the di versity (richness) of coexisting species within a habitat.
Between-habitat diversity is the increased number of species in a region containing several habitats over the number of species in a single habitat, resulting from different species occupying different habitats.
There are also diversity differences between re gions. Species richness (and presumably evenness) generally 22 increases with decreasing latitude, decreasing elevation, or increasing precipitation on large-scale gradients.
These large-scale gradients have been termed ecoclines by
Whittaker (1970).
Several hypotheses have been suggested to explain these diversity gradients, especially the latitudinal gradient. These hypotheses (often incorrectly referred to as theories) are reviewed by Pianka (1966) and are summarized here: (1) Productivity hypothesis. Greater productivity leads to greater diversity, all other things being equal. Since a greater productivity can support more individuals, it will also support more species. This is not in itself an adequate explanation and, in fact, none of these hypotheses seem in themselves adequate. Connell and
Orias (1964) combine this hypothesis with the following hypothesis. (2) The stability hypothesis (Klopfer, 1959).
A more stable physical environment will permit a greater degree of adaptation and specialization, enabling a greater number of species to coexist through finer resource par titioning. (3) The predation hypothesis (Paine, 1966).
A greater number of predators will reduce prey populations to the point where interspecific competition becomes un important and coexistence can be tolerated between com petitors, therefore allowing greater numbers of species to coexist. (4) The competition hypothesis (Dobzhansky, 23
1950). This hypothesis assumes that competition is more
intense in the tropics. Since the physical environment
is not limiting, it must be the biotic competition is
limiting. When competition is intense for resources, specialization is highly advantageous and increased speciali
zation permits more species to coexist. (5) The spatial
heterogeneity hypothesis (MacArthur, 1965; Simpson, 1964).
A more complex topography contains more habitats and thus more species. Simpson (1964) has argued that because of topographic heterogeneity, the tropics also contain tem
perate and polar habitats. On a smaller scale, a complex
habitat has more opportunities for specialization than a
simple habitat, and thus more species. Kohn (1967) showed a relationship between substrate complexity and the number of species of Conus on Pacific Ocean reef platforms.
MacArthur (1965, and elsewhere) has demonstrated a rela tionship between structural complexity of vegetation and breeding bird species diversity. (6) The time hypothesis
(Fischer, 1960; MacArthur, 1965; Pianka, 1966, 1967). The
diversity of an area tends to increase with time. The
time involved can be geological ("evolutionary time theory")
or much shorter ("ecological time theory"). The evolutionary
time hypothesis holds that the number of species increases
with time through speciation and immigration. However, the
higher latitudes have been impoverished by catastrophes 24 such as glaciation and have not had sufficient time to catch up with the tropics (Fischer, 1960). The ecological time hypothesis holds that the number of coexisting species in a habitat is a function of the time available for immigrants to find and colonize the area up to the point at which the area becomes "saturated" with species; and any new immigrants either will not be successful in becoming established, or do so at the expense of established species (MacArthur and
Wilson, 1967; Wilson, 1969; Diamond, 1969). (7) Other hy potheses include (cf. Saunders, 1969) a physically benign climate. Large numbers of species are apparently unable to adapt successfully to harsh environments. C8) On islands, diversity is a function of the area of the island, its isolation from the mainland and other islands (as a source of immigrating species) (MacArthur and Wilson, 1967; Johnson,
Mason, and Raven, 1968), and latitude (Power, 1972).
The factors responsible for global species diversity
gradients are probably some combination of the above listed
factors, and perhaps others. However, the casual factors must also be responsible for local diversity patterns.
Two models used to predict local species diversity are
considered below.
.MacArthur (MacArthur and MacArthur, 1961) attempted
to link BSD to environmental heterogeneity by measuring the
diversity of foliage layers. MacArthur's method worked well 25 enough in eastern deciduous forests that he was able to predict BSD from foliage height diversity (FHD) with his regression equation. Patchiness of the vegetation was a complicating factor (MacArthur, MacArthur, and Preer, 1962).
The method also worked in the tropics, but the vegetation had to be divided into four layers (Orians, 1969). MacArthur
(1964) used the method in the Chiricahua Mountains (eastern
Arizona) and in the desert near Tucson, but found it neces sary to modify his census techniques. Austin (1970) tried the method in the northern Mohave Desert near Las Vegas and found that the foliage layers used had to be modified from
MacArthur's 0-2, 2-12, and >12 foot intervals to 0-3, 3-6, and >6 feet in order to get a near fit with his four data points on MacArthur's regression line.
Tomoff (1971) studied the breeding birds of three creosotebush (Larrea divaricata) habitats in the vicinity of Tucson, Arizona. His three study plots were dominated by creosotebush, but had increasing amounts of other perennials, He found that FHD did not correlate with BSD
in these communities even though several modifications of the method were tried. He reasoned that birds did not
utilize creosotebush, which was the major contributor to the
foliage profile, but instead utilized plants which con
tributed relatively little to the foliage profile, notably
saguaro cacti (Cereus giganteus), cholla cacti (Opuntia spp.), and spinescent trees and shrubs. Since the relative abun dances of these categories seemed to be the important parameter, Tomoff devised a measure which he called physiog nomic cover diversity (PCD). This is the diversity (mea sured by H*) of line intercept coverage of four classes of plant growth forms (stem succulents, evergreen sclerophylls, spinescent shrubs, and "perennials"). Tomoff suggests that since what MacArthur was really measuring with his foliage layers corresponds to the herb, shrub, and tree growth forms in eastern deciduous forests. Thus birds are really re sponding to the diversity of growth forms rather than foliage layers, although the two may be correlated (cf.
Karr, 1968). The increased structural complexity (repre sented by increased FHD) must provide a greater variety of foraging categories in each habitat, enabling more species to coexist. THE STUDY AREA
This study was conducted on a single, complex en vironmental gradient rather than on scattered localities.
On a gradient only a few factors are changing (precipita tion, temperature, soil, etc.) and these are changing in a regular way at a more or less constant rate, thus, hopefully, making the observed patterns easier to understand.
The Tucson Mountains
The gradient selected for study is located on the northwestern slope of the Tucson Mountains, Pima County,
Arizona, and in the adjacent Avra Valley about 20 miles northwest of Tucson. The Avra Valley is a large, flat valley separating the Tucson Mountains on the east and the
Roskruge and Silverbell Mountains on the west. The vegeta tion of the floodplain of the valley is dominated by mesquite (Prosopis juliflora) associations while the re mainder of the valley floor is dominated by simple creosote- bush associations, with the creosotebush sometimes occurring in nearly pure stands. The valley floor is at about 2000 feet (610 m) elevation. The topography slopes gently upward from the valley floor for several miles over an outwash plain of alluvium, termed a bajada. At the top of the bajada, the rocky slopes of the mountains rise steeply
27 28 to a series of peaks, the tallest being Wasson Peak with an elevation of 4687 feet (1430 m). As one proceeds up the
Tucson .Mountains bajada from the west, the desert scrub vegetation slowly changes from creosotebush to more complex saguaro, paloverde CCercidium Jtiicrophyllum) , and bur-sage
(Franseria deltoidea) dominated associations.
The geologically complex Tucson Mountains are com posed of Precambrian Pinal Schist; Cambrian quartzite and limestone; Devonian, Mississippian, Pennsylvanian, and
Permian limestones; Cretaceous anaesite, tuff, sandstone, limestone, and shale; and Tertiary volcanics including rhyolite, andesite, tuff, and basalt (Brown, 1939). The range was originally interpreted as being composed of sedi ments through which a great mass of lava has broken (Mayo,
1968). The orogeny of the Tucson Mountains is the subject of considerable geological debate, however (Mayo, 1971).
Brown (1939) described the bajada as a "sea of alluvium" of two distinct types. Most of the bajada is formed by coarse alluvium or slope wash, which is poorly sorted and of local origin. Slope wash is abruptly re placed by silt on the lower slopes and valley floor. Yang
(1957; Yang and Lowe, 1956), however, found a gradient in soil particle size along his transect from the base of
Wasson Peak northwest into the Avra Valley, indicating that sorting does occur. Yang correlated vegetational changes along his transect with soil particle size. As soil 29 particle size decreases, the capillary spaces between soil particles also decrease. As the capillary spaces become smaller, molecular cohesion between water molecules and soil particles becomes so high that plants are no longer able to extract water from the soil, even though the silty soil of the lower bajada may, in fact, contain more water than the coarser soils higher up on the bajada. Thus a vegetation gradient is created. The plants growing lowest on the bajada would necessarily be those with the greatest powers of extracting water from the soil. Yang recognized two plant communities or vegetation types based on his vegeta tion analysis; a Larrea vegetation type and a Cercidium vegetation type, with a broad ecotone where both are domi nant.
The Tucson Mountains receive on the average less than 12 inches (30 cm) of annual precipitation. This usually comes as thunderstorms during July, August, and
September, and as more gentle rains from Pacific Ocean storms during the winter months. Precipitation is irregular and unpredictable with a great deal of annual variation.
Temperatures can reach 110 degrees F (43 C) in summer.
Night-time temperatures below freezing occur several times per winter, although periods of freezing extending beyond
24 hours are rare and destructive to many plant species 30 when they do occur. Mean annual temperature is about 67°F
(Smith, 1945).
The Study Sites
Five sites were selected on the bajada for in tensive study. The locations of these are given in Table 4 and Figure 4. The study sites were located in undisturbed areas which were also accessable by road. It would have been ideal to locate the sites as close as possible to
Yang's transect. Site 3 was chosen because the ideal site,
3', is the location of a small store. Site 2 was chosen because 2' did not offer a large enough area of homogeneous vegetation. The dashed lines on Figure 2 indicate areas of approximately equivalent vegetation composition. Site 2
is located near the flood plain, so it has a higher com
position of Franseria deltoidea and Prosopis juliflora
than 2', but is otherwise similar. At the beginning of the study it was felt that if everything were changing on the bajada at the same rate, it would be impossible to
isolate the factors responsible for the changes. Conse
quently, the slightly atypical site 2 was retained for the
insights it might provide. Unfortunately, because of
widespread development on the Tucson Mountains bajada,
several other study sites had to be abandoned. 31 Table 4. Location of study sites.
Site Location Elevation
1 T12S,R11E,S15 2050 feet, 625 meters
2 T13S,R11E,S17 2150 feet, 656 meters
3 T13S,R11E,S9 2200 feet, 671 meters
4 T13S,R11E,S10 2300 feet, 702 meters
5 T13S,R11E,S12 2500 feet, 763 meters 32
Avra Volley Road
Twin II Peaks
-x& Twin Peaks
&%&£(<&Saffond Peak's Sr.'-'iu \ . ."A
ontzen
Rudasill Road
Mnnville Road
illjilipllllllipiig T->'asson Pea^ Pca «_/*'•4637
*..1...... ,
miles
Figure 4. Map of study area. METHODS
Daily maximum and minimum temperatures and pre cipitation were recorded near site 5. Plastic rain gauges were set up at the other sites, but were eventually lost either to cracking or vandalism.
Birds were censused using a modified Emlen transect census (Emlen, 1971). At each site, a transect line 800 m long was laid out in such a direction as to intersect the washes at about a 45 degree angle when possible. This was done to prevent the washes from being either over- or under-represented in the censuses, since a greater number of birds are found along washes in desert habitats (cf.
Raitt and Maze, 1968). All birds seen or heard within
400 feet (120 m) on either side of the transect line were recorded. Birds heard, but not seen, were not counted un less the obseryer was certain they were within 400 feet.
All censuses were in early morning at the time of greatest bird activity, usually about a half an hour to an hour after sunrise. The censuses took from 20 minutes to an hour, depending on site and season. Censuses were not made on days with weather conditions which might depress bird activity. Relative bird populations from census data were used for site comparisons. Repeated censuses in one
33 34 area indicated that three censuses were an adequate sample and additional censuses did not alter diversity values sig nificantly. Since each census represents an increase in area sampled, the number of species increases as in a typical species-area curve. Therefore, for comparisons to be valid, a similar number of censuses had to be com pared, and this was standardized at three. A standard sample of three censuses was made at all five sites during
February, March, May, June, July, October, and December
1972. Breeding bird diversity was calculated from census results, locations of paired singing males, and nests found. The breeding season extended from March to July
Cat least) and not all species were breeding simultaneously, further complicating matters.
Rodents were censused by live trapping, toe clipping, and release. Fifty live traps were placed 16 m apart along the 800 m transect line described above. Three nights trapping was found to be an adequate sample for comparative purposes and additional trapping did not greatly alter diversity values. These results however, are in no way considered a complete census of the rodent populations at each site. Rodents were censused at each site except site
4 during June and October. Site 4 was censused in October only. Traps were baited with peanut butter and oatmeal and were checked at sunrise. Each individual captured was 35 identified, sexed, and given a unique combination of clipped toes. Trapping during periods of full moonlight was avoided.
Lizard populations were censused using an adapta tion of Eralen's (.1971) bird transect census. The observer walked slowly out along the 800 m transect line about 50 m to one side of the center line and then back 50 m out on the other side of the center line to give a total transect of 1600 m for each site. When a lizard was sighted its
identity and distance from the line of travel were noted.
Distances were paced if uncertain. Lizards beyond 15.5 m
(50 feet) from the line of travel were not counted. This gave a strip transect area of 5 hectares (1600 m x 31 m).
A histogram was made for the number of individuals of each
species observed per unit distance from the line of travel
for the combined censuses done on each area. From these
histograms, it was apparent that the observability of each
species decreased as a function of distance from the ob
server. The number of individuals was averaged over the
first five meters and this number was multiplied to give
the hypothetical number of individuals in the census strip.
The number actually counted divided by the hypothetical
total gives the coefficient of detectability (CD) value.
The CD value is then divided into the average number of
individuals per species observed per census to give the 36 number of individuals per 5 hectares. As might be expected, different species in different habitats had very different
CD values. Censuses were made in "early mid-morning" during June and July while lizards were at the peak of morning activity. The exact time varied somewhat depending on daily weather conditions. The method probably under- represents semi-arboreal species (Uta stansburiana,
Urosaurus ornatus) and cryptic species (Phrynosoma solare),
but seemed to work especially well with the two common ground-dwelling lizards, Cnemidophorus tigris and Callosaurus draconoides. The other species found at the study sites,
Dipsosaurus dorsalis, Sceloporus magister, Crotaphytus
wislizeni, Heloderma suspectum, and Coleonyx variegatus, were seldom encountered. The results obtained with this method are comparable to results obtained by walking a 4-
hectare grid near site 5 in September 1971, and to results
obtained by Pianka (1970) for Cnemidophorus tigris near
Casa Grande, Arizona.
Ant populations were estimated by counting the num
ber of colonies of each species along the 800 m transect
line and within 10 m on either side of the transect line.
Colonies of smaller species were located by following
workers to the entrance, turning over rocks, looking under
bur-sage (Franseria deltoidea) and in other likely locations.
Frequently, a nest was found with no workers at the surface. 37
In cases of uncertainty about the identity of the nest,
I waited a few minutes for workers to appear, then began
excavating with a spoon until workers were located. I
was able to identify workers of all but two of the 23
species with a small hand lens; no attempt was made to
separate Myrmecocystus depilus and M. placodops. Colonies
of many species had multiple entrances and arbitrary
criteria had to be adopted for delimiting colonies. The
same criteria were applied throughout, however, so the
results are comparative. The criterion used was that if an
entrance was separated from its nearest neighbor by more
than the diameter of the cluster that the neighbor belonged
to, it was considered a separate colony. This gave in
tuitively acceptable results. The ant censuses were made
early in October while ants were still active.
Foliage arthropods were sampled at each of the
sites in mid-September when insect populations were at, or
near, the annual peak. Sampling was done with a standard
12" sweep net with a reinforced, heavy-duty bag. Sampling
was accomplished by walking in a straight line, sweeping
all vegetation encountered, except for ocotillo (Fouquieria
splendens) and all species of cacti. Sampling was thus in
approximate proportion to the foliage volume of each species
in the community. The bag was emptied after every 100
sweeps and 10 such subsamples were collected for each site. 38
Whittaker (.1952) has discussed the shortcomings of sweeping as a collecting method, but he concluded, as did I, that it was still the most suitable method for comparing insect communities.
Perennial vegetation was sampled by ten, 0.1 hectare (20 x 50 m) quadrats at each site. Quadrats were located along the 800 m transect line at intervals de termined by adding successive two-digit numbers from a random number table. Individuals of each perennial species, except for root perennials and grasses other than Muhlen- bergia Porteri, were counted. The long sides of the quadrat were used for line-intercept coverage data. Data obtained is thus for canopy coverage rather than for cover in the strict sense, since the canopy often contains gaps between leaves (Greig-Smith, 1964).
Foliage height diversity was measured in the manner described by MacArthur (MacArthur and MacArthur, 1961;
.MacArthur, et al,, 1962) except that measurements were made in two-foot intervals up to 12 feet so that several com
binations of layers could be tried. Six measurements were made at each height interval at every 100 meter mark along the 800 m transect (plus two extras for a total of 50 mea surements for each height interval) at each site. The six
lines of measurement at each point were at 60 degree angles
from each other. 39
Spring and summer annuals were censused using 50 one-meter square quadrats spaced every 16 meters along the transect line at each site. The contents of each quadrat were separated by species, counted, and put in a separate plastic bag. Upon return from the field, the specimens were oven dried for 10 days at 46°C and then weighed. Spring annuals were sampled March 16-25, 1972 and summer annuals were sampled 19-25 September 1972. Sampling was done at the end of each growing season.
Nomenclature for plants follows Kearney and Peebles
(1964) except for cacti, which follow Benson (1969) and
Larrea divaricata is used in place of Larrea tridentata
(Felger and Lowe, 1970). Nomenclature for mammals follows
Cockrura (1964) and lizards follow Stebbins (1966). Common names for birds follow the American Ornithologist's Union check list fifth edition (1957). Ant nomenclature is partly from Creighton (1950) and partly from R. R. Snelling
(pers. comm.). Nomenclature of other invertebrates is from diverse sources, including specimen determination labels, general works, monographs and revisions. Voucher speci mens of plant species will be deposited in the University of Arizona herbarium. THE DIVERSITY PATTERNS
Breeding bird species and number of individuals increase steadily with elevation on the bajada (Table 5 and
Figs. 5 and 6). The diversity values (H'), however, do not follow this pattern; diversity increases rapidly on the lower bajada and then almost levels off (Fig. 7). Peren nial plants and foliage arthropods also showed a similar pattern (Appendices VI and VII, and Figs. 7 and 8). This pattern is a result of the dominance of a few species at the highest sites. Thus although the number of individuals and species are increasing, the high relative abundance of a few species lowers the evenness component, and hence the value of the index.
Seasonal diversity was lowest at most sites in early spring, partially due to large flocks of wintering
fringillids, notably Brewer's Sparrows (Appendix II), and
also because of low populations of resident birds. Diversity was highest (Table 6 and Fig. 9) during the breeding
season at the higher sites, and just after the breeding
season in the lower sites. Large numbers of fledgling
Cactus Wrens, Verdins, and Curve-billed Thrashers in
creased population levels at the higher sites and thereby
decreased post-breeding season diversity. Presumably,
40 41
Table 5. Number of individuals (number of pairs x 2) of breeding birds at the five study sites on the Tucson Mountains bajada, spring and summer, 1972. — Data from a combination of census results, locations of paired singing males, and nests found in 800 x 1.24 m bird transect plot.
Study Site Species 12 3 4 5
Red-tailed Hawk ---11
Sparrow Hawk - - - - 1
Gambel's Quail - - - 1 3
White-winged Dove - 2 1 1 3
Mourning Doye - 2 2 3 2
Roadrunner --111
Lesser Nighthawk - - - 1 -
Gilded Flicker - 2 3 5 6
Gila Woodpecker - - 3 6 8
Wied's Crested Flycatcher - - - - 1
Ash-throated Flycatcher - 2 1 1 4
Purple Martin ---24
Verdin 2 3 5 5 6
Cactus Wren 2 6 5 10 14
Curye-billed Thrasher 1 2 2 8 6
Black-tailed Gnatcatcher - 2 3 3 2
Loggerhead Shrike - 11 1
Scottls Oriole — - - - 2
Brown-headed Cowbird - - 2 2 1 42
Table 5, (.Continued)
Study Site Species 12 3 4 5
House Finch 2 - 1
Brown Towhee - - 1 2 3
Rufous-winged Sparrow - - - - 2
Black-throated Sparrow 2 4 2 2
Total Individuals 5 24 39 55 73
Species 3 10 15 18 21 lizards -
X
k-
2100 2200 2300 2400 2500 Elevation (feet)
Figure 5. Vertebrate populations. — Total indi viduals of birds (per 40 ha.), rodents (October), and lizards (per ha.). 44
/ xsAn
izafds ^
I I I I I I I III 2100 2200 2300 2400 2500 Elevation (feet)
Figure 6. Number of species at each site. — Foliage arthropods should be multiplied by six. 45
4.00 . /° acffl***18-' - / o / / / 3.50 " /
3.00 -
2.50 •
H 2'00-
1.50 •
1.00 .
.50 -
, , , 1 \ 2100 2200 2300 2400 2500 Elevation (feet)
Figure 7. Species diversity (H*) of breeding birds, rodents, ants, and foliage arthropods. 46
2.50
.spring X- 2.00 - SOQoaJW/S /; •-X
1.50 -
- O as ^erenni?^
1.00 -
lizards -•
annuals .50 .•
—, , 1 i i 2100 2200 2300 2400 2500 Elevation (feet)
Figure 8. Species diversity (H') of lizards, perennial plants, spring annuals, and summer annual plants, 47
Table 6. Seasonal changes in bird species diversity (H1) values at the five study sites.
Study Site Census Period 12 3
February 0.95 1.43 2.28 1.91 2.01
March 0.84 1.90 2.11 2.31 1.82
May 1.06 2.31 2.44 2.42 2.58
June 1.77 2.11 2.36 2.30 2.31
July 2.10 2.40 2.14 2.28 2.29
October 2.06 2.21 2.32 2.23 2.06
December 0.93 1.85 1.60 2.29 2.27
Mean Diversity 1.387 2.030 2.179 2.249 2.191
Breeding Diversity 1.06 2.19 2.59 2.57 2.74 0
0
0
Site H
0 F M A M J J A S 0 N D
Figure 9. Seasonal variation in bird species diversity (H') at the five study sites during 1972. mortality, emmigration, and flock formation by resident birds and immigration of wintering fringillids in fall and winter further lowered diversity values. Field observa tions indicated that young individuals .moved down the bajada late in the breeding season, increasing the diversity of the lower areas for a time. This .migration of young birds into less favorable habitats may be a result of older birds holding territories in the better habitats, and also normal dispersal. The greatest fluctuations in diversity were in the simplest habitats.
Rodent population and diyersity patterns were similar in June and October (Figs.5,6 and 7 and Table
7, and Appendix III). Numbers of individuals, species, and diversity generally increased with elevation. However, data for sites 2 and 3 show a minor reversal in the trend in both June and October. The October data also show a minor reversal between sites 4 and 5.
Lizard populations increase steadily with elevation
(Fig. 5), but species numbers (Fig. 6) and diversity (Fig.
8) show a curious "zig-zag" pattern. Two explanations seem possible; (1) The sample was not adequate and the results do not reflect the true pattern. (2) The diversity fluctuation along the gradient is real and reflects varia tion in some environmental variable. There is evidence for both possibilities. The census technique is admittedly Table 7. Diversity values (H1) of the major community components studied at the five study sites.
Study Site Group 1 2 3 4 5
Birds (breeding) 1.056 2.189 2.593 2.572 2. 738
Rodents (June) .763 .934 .666 a 1.623
Rodents (October .312 .837 .703 1.474 1. 317
Lizards 1.004 .604 1.105 .671 • 686
Ants 2.064 2.291 2.027 2.128 1.761
Foliage arthropods 3.347 3.658 4.029 3.829 3.997
Perennial plants .352 .704 1.267 1.120 1. 247
Annual plants (spring) b 1.153 2.040 2.068 1.862
Annual plants (summer) 1.161 .323 .903 .553 569
aSite 4 was not censused for rodents during June.
t. Part of data from site 1 lost, diversity not calculated (see text). biased toward the large, open-ground species. However, the results should be relative and comparable between sites. If the diversity pattern shown is in fact real, some interesting relationships emerge. For example, the rodent and lizard patterns counterbalance each other and the rodent pattern parallels the pattern of bursage density
(Fig. 10). This suggests that perhaps the cover provided by bur-sage is important to rodent populations and when rodent populations are lower, lizard populations can be higher. This will be discussed in more detail later.
Ant populations also show an unexpected pattern
(Figs. 6, 7, 11 and Appendix V). The number of colonies increases rapidly, peaks low on the bajada, and then drops to fairly low levels higher on the bajada. Diversity generally declines higher on the bajada with the reduction of number of colonies of most species. Pheidole -xerophila and Novomessor cockerelli remain abundant, however, re ducing evenness and the value of the index. Species num bers are a problem, however. Although the census results show the relative numbers of species at each site, con siderable additional time was spent collecting at site 5, while learning the ant fauna preparatory to making the census. As a result of this extra collecting, six addi
tional uncommon species were collected at site 5. Whether
these species are also present at sites 4, 3, and 2 is not 1.50 - *6000
1.25- •5000
1.00- -4000
\/ V x //
° \ h /' -3000 x i \ / f\ » ' . / / 1 \ I \ / / * o I ikords.
.50" - 2000
.25" 1000
—i 1— 2100 2200 2300 2400 2500 Elevation (feet)
Figure 10. Relationship between rodent and lizard diyersity patterns and bur-sage (Franseria deltoidea) density. 53
1200
1000 -
800
b 600
400
200
\, ant colonies ^
2100 2200 2300 2400 2500 Elevation (feet)
Figure 1L Arthropod populations. —Total number of ant colonies per 1.6 ha. and foliage arthropod indi viduals per 1000 sweeps. 54 known. Site 1 seems to have a limited ant fauna. It is felt that exhaustive collecting would show a gradual in crease in species with elevation. One alternative hypothesis
is that the rare species are present over the entire bajada,
but are very uncoramon and drop out in the creosotebush vege tation type. A third hypothesis is that the census results reflect the true number of species. In any case, these species are present in very low numbers and with the ex ception of Neivamyrmex nigrescens, an army ant, they probably have little impact on the community. It thus appears that
conditions are most favorable for ants lower on the bajadas.
Foliage arthropod species, individuals, and di
versity generally increased with elevation on the bajada
(Figs. 6, 7, 11 and Appendix VI). The low numbers of in
dividuals at site 2 may be partially a result of the high
proportion of bur-sage to creosotebush in that habitat.
Bursage does not seem to be as productive of insects (per
sweep) as creosotebush, especially if the bursage is small
and scattered rather than forming a dense cover. A pos
sible antagonistic relationship between ants and foliage
arthropods is another possibility.
Quadrat sampling showed a gradual increase in num
bers of perennial plant species, numbers of individuals and
percent coverage with increase in elevation (Figs. 12
and 13 and Table 8). The species diversity, pattern was 55
8000
7000 "
6000 -
r-j 5000 "
4000 •
S 3000 &
2000 •
/y
1000 '
x~-——- _ " ""
2100 2200 2300 2400 2500 Elevation (feet)
Figure 12. Plant populations. — Total individuals of perennials per hectare and spring and summer annuals per 50 m2. 56
2100 2200 2300 2400 2500 Elevation (feet)
Figure 13. Perennial plant coverage. — Line intercept data from the five study sites. 57
Table 8, Perennial plants: canopy coyer as a percentage of one kilometer of line intercept at each site.
Study Site Species 1 2 3 4 5
Acacia constricta - 1.37 2.21 2.98
Acacia Greggii - - - - .03
Celtis pallida - - - 1.22
Cercidiura microphyllura - .49 4.90 7.25 11.53
Cereus giganteus - - - .30 .33
Condalia lycioides - - - - .17
Echinocereus Fendleri - .03 - .01 -
Ferocactus Wislizenii - - - .05 -
Fouquieria splendens - - - - .20
Franseria deltoidea .04 8.93 1.59 14.98 23.82
Franseria dumosa - - 3.36 - -
Hymenoclea pentalepis - .03 - - .92
Janusia gracilis - - .04 .41
Jatropha cardiophylla - - - .59
Krameria Grayi - - - 2.25 .12
Larrea divaricata 21.09 11.29 17.96 10.98 3.44
Lycium Berlandieri - - - - .05
Muhlenbergia Porteri .01 .08 2.10 .28 3.64
Olneya Tesota - - 2.43 .06 3.63
Opuntia arbuscula - .11 .07
Opuntia fulgida - - - .19 .53 58
Table 8, (.Continued)
Study Site Species
Opuntia leptocaulis - .09 - .14 .14
Opuntia phaeacantha - - - - .71
Opuntia versicolor - .06 - .38 1.68
Phorodendron californicum .04 - - .09 .08
Prosopis juliflora .95 1.12 ,92 - -
Zinnia pumila - - .19 -
Total Cover C%) 22.13 23.49 33.45 39.32 56.39 59 similar to the bird and foliage arthropod patterns. In this case, the failure of the index to keep pace with in creasing richness and numbers of individuals is a result of the large Franseria deltoidea populations, which reduced equitability, Populations of Cereus giganteus, Opuntia spp,, and Cercidium niicrophyllum, which are especially important to birds as nest sites, increase jaore rapidly with eleyation than bird populations, indicating that bird populations are limited by other factors than nest site availability on the upper bajada (cf. Tomoff, 1971).
The number of individuals and species of spring and summer annuals show opposite patterns (Figs. 8, 12, Table
9, and Appendix IX). Diversity (Fig. 8) of spring annuals increases rapidly, levels off, then decreases. A portion of the data from site 1 for spring annuals was lost. The estimate shown in Table 9 and Figure 8 is an extrapolation based on the six remaining samples. It is in agreement with my recollection of the lost data. Diversity of summer annuals shows the same pattern as lizards. It is difficult to see why lizards and summer annuals should show the same unusual pattern (Fig. 10).
Foliage height diversity was calculated first using MacArthur's layers (MacArthur and MacArthur, 1961):
0-2, 2-25, and over 25 feet. His modification (MacArthur et al., 1962) was next tried: 0-2, 2-12, over 12 feet. Table 9. Spring and summer annual plant numbers, species, and biomass per 50 one-meter square quadrats at each site. — Biomass is oven dry weight in grams.
Study Site Category 1 2 3 4 5
Spring annuals: individuals 7000a 2783 896 491 227
Spring annuals: species 13 18 17 13 13
Spring annuals: biomass 1320 530 260 130 25
Spring grasses: biomass'3 34.4 91.1 100.5 189.1 586.7
Summer annuals: individuals 551 881 823 1113 3403
Summer annuals: species 6 8 10 9 13
Summer annuals: biomass 102.3 237.4 181.7 262.4 68.9
aEstimated, see text.
bSpecies not tallied separately. 61 Several othex combinations of layers (Table 10) were tried.
The low PHD values for sites 4 and 5 are a result of the
dense growth of Franseria deltoidea, which lowered the value of the index, and may be of little importance to birds.
Since Larrea divaricata may also be of minor importance to
birds (Austin, 1970; Tomoff, 1971), the 0-4 foot layer was
eliminated in one of the combinations of layers tried.
None of the combinations tried would successfully predict
BSD, although this last combination did improve the fit of
the data to MacArthur's regression line somewhat,
Tomoff's (1971) suggestion of using physiognomic
cover diversity (PCD) to predict BSD was followed using the
coverage data from Table 8. Tomoff used four categories
of plant growth forms. Since the sites under investigation
contained a great many more species than Tomoff's study
areas, PCD was also calculated using several additional
categories of plant growth forms (from Whittaker, 1970).
(.See Appendix VIII for a list of plant species and their
life form classification under both systems.) If only four
categories are used, the increase in species is largely in
the category "perennials", which reduces the evenness.
With ten categories, the miscellaneous "perennials" cate
gory is broken up into more meaningful physiognomic units.
Physiognomic categories are artificial units, however, and
more than ten categories could be utilized. The logical Table 10. Foliage height diyersity (H') using various per mutations of layers. — Layers represent foliage density at the indicated distance above ground (in feet).
Study Site Layers 1 2 3 4 5
0-2, 2-25, 25+ .691 .632 .672 .579 .414 1 1 0 H to to to * 12+ .691 .756 .931 .826 .596
0-2, 2-6, 6+ .806 .896 1.015 .867 .557
0-2, 2-4, 4-12, 12+ .997 1.013 1.253 1.124 .806 1 1 0 CTl to to 6-12, 12+ .829 1.013 1.220 1.026 .761
0-2, 2-4, 4-6, 6-8, 8-10, 10-12, 12+ 1.196 1.511 1.773 1.646 1.246
4-6, 6-8, 8-10, 10-12, 12+ .859 1.531 1.533 1.582 1.569
Table 11. Physiognomic cover diversity (PCD) values obtained using four and ten categories of growth forms and species cover diversity (SCD) values. — For a listing of species and categories, see Table 7 and Appendix VIII.
Study Site Category 1 2 3 4 5
PCD 4 .201 1.020 1.009 1.163 1.047 PCD 10 .209 1.085 1.140 1.348 1.529
SCD .206 1.182 1.481 1.584 1.425 end would be to haye each physiognomic unit contain only a single species. The diversity of cover for each species could be termed "species cover diversity" (or SCD).
Tomoff's PCD )PCD-4), ten-category PCD (PCD-10), and
SCD were calculated for each site (Table 11). BSD was significantly correlated (Figs. 14, 15, and 16) with all three measures; PCD-10 and SCD gave increasingly better fits than PCD-4, however. Diversity of coyer thus seems to be highly correlated with BSD, even though FHD is not.
However, it is interesting to note that the number of plant species is also a good predictor of both bird species richness (Fig. 17) and BSD (Fig. 18), contrary to the results of MacArthur (MacArthur and MacArthur, 1961
MacArthur et al., 1962; MacArthur, 1964). 64
0
.5
0
.5
.0
1.706 x +.720 .965 .5
.5 1.0 1.5 2.0 2.5 PCD - 4 (H1)
Figure 14. Regression of bird species diversity (BSD) on physiognomic cover diversity (PCD-four categories). 65
.0
5
0
1.0 1.320 x +.828 .9 78 p <. 01
.5
.5 1.0 1.5 2.0 2.5 PCD - 10 (H')
Figure 15. Regression of bird species diversity (BSD) on physiognomic cover diversity (PCD-10 categories). 66
3.0
2.5
2.0
1.5
1.034 x +.910 1.0 .985 p <.01
.5
.5 1.0 1.5 2.0 2.5 SCD (H<)
Figure 16. Regression of bird species diversity (BSD) on plant species cover diversity (SCD). 901 x -6.24 977 <.01
•H
10 -
T T 10 20 30 Number of Plant Species
Figure 17. Regression of bird species richness on number of plant species. 3,0
.5
2.0
1.5 085 x +.377 955 p <.02
1.0
.5
10 20 30 Number of Plant Species
Figure 18. Regression of bird species diversity (H *) on number of plant species. DISCUSSION
When the field work for the present study was begun, three diversity patterns were expected: (1) Di versity would steadily increase with elevation along the vegetational gradient. This pattern was expected for most groups of organisms. (2) Diversity would steadily de crease along the vegetational gradient. It was thought that some groups, such as lizards might show this pattern,
(3) Diversity would remain unchanged over the entire tran sect. It was thought that some opportunistic groups, such as annual plants, might exhibit this pattern. Nature, however, did not resolve itself into such, simple patterns
(Figs. 7 and 8). The observed patterns did not closely correspond to any of the expected patterns. Instead, six more or less distinct diversity patterns were found:
(1) Breeding bird diversity increased rapidly up to site
3, then increased very slowly on the upper bajada.
(2) Perennial plant and foliage arthropod diversity in creased more slowly up to site 3, then nearly leveled off.
(3) Rodent diversity increased from site 1 to site 2, decreased to site 3, then increased again. (4) The spring annual pattern is incomplete, but resembles the breeding bird pattern. (5) Ant diversity generally decreases with
69 70 elevation, but with minor reversals in the trend. (6)
Lizard and summer annual diversity first increases with elevation, then decreases, then increases, then decreases again, and finally levels off.
Several authors (Sanders, 1968; Margalef, 1969) have expressed the opinion that the diversity of a suf ficiently large taxonomic segment or a community ("taxo- cene" of Whittaker, 1972) is representative of the entire community, so that bird diversity would be similar to the mammal, insect or flowering plant diversity in that com
munity, relative to other communities. This study has shown that this assumption is unfounded. Although certain taxonomic groups have similar patterns, others do not.
Just in the groups examined in this study, six distinct diversity patterns were found.
The presence of several distinct diversity patterns
on the bajada suggests that various groups of organisms
may be better competitors in one habitat than another.
The lower bajada has few nest sites for birds, lacks a
wide range of foraging locations, does not provide much
protective cover, and has fewer arthropods present for birds
to eat. Birds that do occur there are most frequently
found in the relatively dense vegetation along the washes.
Only a few species of plants are producing seeds for the
heteromyid rodents, so there are fewer species of rodents lower on the bajada. However, ant and lizard diversity is higher on the lower bajada, thus countering the trend of other consumers. Pianka (1971) found a similar situation in the Kalahari Desert of Africa where lizard diversity ran counter to bird species diversity along a vegetational gradient. Under increasingly arid conditions, vegetation becomes increasingly more open and less diverse, but lizards become unexpectedly more diverse. He postulated that competition with ground-dwelling insectivorous birds may be responsible for this, although alternatively, it may simply be that lizards require a certain amount of open space for basking and foraging. The relationship between lizard diversity and rodent diversity and bur-sage
(Franseria deltoidea) density (Fig. 10) was pointed out earlier. If bur-sage density is taken as an index of the amount of open ground at ground level, then lizard diversity is closely related to the amount of open ground. The amount of open ground might in some way be effecting the amount of seeds available to rodents, thus producing an opposite effect on rodent diversity. The evidence thus seems to
indicate that instead of all groups of consumers reflecting
producer diversity, there is a "trade-off" between at least
some consumer groups. This "consumer trade-off" is
illustrated by rodents and lizards, and ants and foliage
arthropods in the present study, and by lizards and birds in the Kalahari Desert. Examination of the diversities of other communities should reveal other examples of this phenomenon.
Other factors responsible for species diversity must also be considered. Several hypotheses used to ex plain diversity were discussed earlier. A complex inter play between productivity, time, environmental stability, heterogeneity, competition, predation, and physical stress must determine the diversity of a taxonomic group in a given community.
It is clearly beyond the scope of this study to work out quantitatively the influence on diversity of these various factors. However, steps in this direction have recently been made by Pianka (1967) and Power (1972).
Pianka has evaluated eight diversity hypotheses and their effect on lizard diversity and has concluded that hetero geneity of the habitat (especially vegetation) and length of the growing season are the most important factors.
Power used multiple regression techniques to analyze fac tors contributing to the number of bird species on islands off the coast of southern California and northern Baja
California. He found that island area contributed 68.2%,
latitude 15.3%, and unknowns 16.5% to the number of plant
species. Plant species richness contributed 66.8% to the
number of bird species, while isolation from the mainland contributed 14.2%, and unknowns 19.0%. These studies indicate the importance of vegetation to animal diversity.
Thus the vegetational gradient of the Tucson
Mountains bajada may be largely responsible for the observed consumer diversity patterns. (Although vegetation may have a different effect on the diversity of each group.)
Yang (.1957; Yang and Lowe, 1956) explained the vegetational diversity gradient on the basis of a soil particle size gradient. Dr. J. R. Hastings (pers. comm., 1973) suggests a temperature hypothesis instead: the vegetational gradient reflects the temperature tolerances of the plant species.
Since cold air sinks to the valley floor, freezes are more intense there. This is not to deny the importance of edaphic factors, however. The importance of water stress on the lower bajada is obvious, even to the casual observer.
Plants which are widespread on the upper bajada become re stricted to washes lower on the bajada, and finally drop out. Water stress and freezing temperatures acting to gether must intensify the gradient.
However, the basic question of why there isn't just one single, very abundant plant species on the entire bajada roust be considered. Why, for example, isn't Larrea divaricata the only plant on the bajada? It could be very abundant on the upper bajada and gradually become smaller and .more widely spaced on the lower bajada. The logical answer must be that other species, such as Cercidium microphyllum, with very different adaptations (root sys tems, canopy height, freezing tolerance) would be tapping resources (water at a different depth, sunlight at a dif ferent height) not utilized by Larrea. By this means, a number of species could coexist. But with each addition, additional overlap in resources being utilized (water, sunlight, minerals, space) must be occurring. Consequently, competitive interactions become increasingly important.
Furthermore, predators (herbivores) are reducing popula tion sizes by removing foliage and seeds, thereby de creasing competition, allowing more coexistence, and increasing diversity (provided that predation is working at least in part on the dominant species). Eventually, a whole chain of factors (time, size of the species pool, productivity, environmental predictability, and others) comes into play. The question then becomes the converse: what limits diversity? The answer must be that many plant species are not able to extract water from the increasingly fine-textured soil under conditions of high temperatures and low humidity and still survive the occasional freezing temperatures. We must then ask why more species do not adapt to these conditions and why more species adapted to these conditions do not move in and saturate the environ ment, Sanders (1968:259) suggests that many species are 75 unable to adapt to physiologically-limiting and unpre dictable environments because of differences in genetic variability.
A lucid genetic interpretation for the re lationship of environmental stability to diver sity has been given by Grassle (1967). He pointed out that populations present in physically stressed and unpredictable environments show broad adaptations to these conditions by main taining a high degree of genetic variability. Thus, even though the stress may be expressed in a variety of ways, a portion of the poly morphic population will probably survive. These genetically flexible species are opportunistic and cosmopolitan, and they have little tendency to speciate.
The price paid for this variability is "the genetic load or loss of fitness relative to the maximum in a more uniform environment." In stable environments "the expression of deleterious genes outweighs the advantages obtained from maintaining genetic flexibility." Therefore, in stable and predictable environments, such genetic variability will be selected against.
This suggests that the fact that more species do not adapt to rigorous environments may have a genetic explanation.
It is interesting to note that the species which were common in the most "rigorous" habitat (site 1) (Larrea divaricata, Cnemidophorus tigris, Dipodomys merriami,
Perognathus penicillatus, Cactus Wren, Curve-billed Thrasher,
Verdin) were also common over the entire bajada. They are also widespread geographically and they are "generalists" rather than "specialists." It is possible that the genetic interpretation given above would be applicable here. Another explanation for the observed distribution of species is that vegetation structure determines how finely the habitat can be subdivided. A more complex vegetation structure means that there are more possible ways of utilizing the resources in that habitat, and also a greater range of resources to be utilized. Therefore, .more specialized species can be added and diversity increases. Vegetation, and especially its structure, becomes of special importance in explaining diversity patterns.
Since MacArthur's predictive model based on heterogeneity of foliage layers does not seem to predict
Sonoran Desert BSD, three measures of coverage (PCD-4,
PCD-10, and SCD) were tried and were found to be a more successful approximation of the factors ultimately re sponsible for BSD. My interpretation of the relationship between coverage diversity and BSD is that a high diversity of cover indicates (1) structural complexity of vegetation and thus more opportunities for foraging specialization by subdivision of space, (2) a greater variety of nesting substrates, (3) a greater variety of food resources, and
(4) the relative importance of each plant species. The greater variety of food resources is a result of both a greater variety of plant species producing seeds and foliage, and a greater variety of insects and other herbivores associated with the plants which would then be available to
birds. The greater variety of food resources would also 77 mean a more stable (in the sense of alternate food sources) food supply in that habitat. The idea that diversity in creases the stability of a biological community is wide spread in the ecological literature. In view of this, it is interesting to note that the greatest seasonal changes in bird diversity (Table 6 and Fig. 9) were in the least diverse habitats. The relative importance of each species, as indicated by its coverage, may be quite important in the
Sonoran Desert where nearly every species has a different growth form. In eastern deciduous forests, where MacArthur and his colleagues did much of their work, the growth forms of the plant species not as variable, and structure per se may be more important to birds than species composition.
In the Sonoran Desert, structure may still be more important than species composition, but structure and species com position are more nearly equivalent, and diversity of foliage layers is no longer an adequate measure of struc tural complexity or resource diversity.
The data also show other relationships which should
be examined for predictive value. For example, there is a
close relationship between the number of perennial plant
species and the number of bird species (Fig. 17). Perennial
species diversity and bird species diversity do not correlate
especially well, whereas just the number of species do.
Power (1972) explained 66.8% of bird species richness by 78 plant species richness. Arthropod species numbers also parallel bird and perennial richness, but not as closely.
The number of insects at each site could be thought of as an index of the food available for insectivorous birds.
This increases dramatically with elevation on the bajada, and increases faster than bird numbers or species and is hardly reflected by bird species diversity.
A predictive explanation for diversity is of interest for practical and theoretical reasons. Hill
(1973:431) has stated, "diversity is of theoretical interest because it can be related to stability, .maturity, produc tivity, evolutionary time, predation pressure, and spatial heterogeneity." Margalef (1958) went even further and emphasized that diversity (H') is a measure of the organiza tion (or information) in a community. Diversity seems to be a fundamental part of community organization, but before it can be understood, the confusion regarding its mathe matical measurement (which index to use) and its biological measurement (which entities to measure) must be resolved.
Then answers to more meaningful questions may be attempted.
However, because of the "diversity" of diversity
patterns, it is difficult to conceive of a model which would be able to predict diversity of birds, mammals,
lizards, and insects equally well. Since heterorayid rodents,
harvester ants, and seed-eating birds may all compete for the same resources, it may make more sense, ecologically, to talk about granivore or insectivore diversity rather
than bird or mammal species diversity. The problem then
becomes (after deciding how to classify each species
trophically) one of comparing insectivore diversities in
habitats A, B, or C, for example. This, I believe, will
be a more productive approach to an understanding of
species diversity. SUMMARY AND CONCLUSIONS
Ten species diversity indices were discussed and compared using hypothetical and actual species abundance distributions. Using the criterion that an index should
(1) increase proportionally with increasing species numbers, (2) increase proportionally with increasing numerical equality between species, and (3) increase proportionally with both increasing species numbers and numerical equality acting in combination, only two of the indices, D and H<, were satisfactory. Of these, the s information theory measure, H1, was selected for use in this study since it has been widely used and would facili tate comparisons between studies.
Species diversity values were determined for birds, rodents, lizards, ants, foliage arthropods, peren nial plants, spring annual plants, and summer annual plants at five study sites along a complex environmental gradient located on the northwest-facing bajada of the
Tucson Mountains, Arizona. The diversities of perennial
plants and foliage arthropods increased with elevation
on the lower bajada, but leveled off on the upper bajada.
Bird diversity increased rapidly on the lower bajada, then
increased more slowly on the upper bajada. Rodent
80 81 diversity increased with elevation, except for a decrease between two of the sites. Ants generally decreased in diversity with elevation. Lizard and summer annual diversities decreased, increased, decreased, then leveled off. Spring annuals increased very rapidly with elevation on the lower bajada, leveled off, then slightly declined in diversity. These results show that the diversity of one community relative to other communities cannot be judged from a single group of organisms.
The observed diversity patterns suggest that there is "consumer trade-off" between consumer groups. In areas where lizard diversity was low, rodent diversity was high, and vice versa. This reciprocal relationship was also seen between ants and foliage arthropods. The reasons for consumer trade-off are not known, but two hypotheses are that (1) some groups are more efficient competitors in some habitats than others, and (2) simple differences in habitat requirements may account for the differences between groups. For example, vegetation density near the ground may be important to lizards and rodents.
Two predictive models of bird species diversity
(BSD) were tested. MacArthur's foliage height diversity
(FHD) model did not successfully predict BSD, whereas
Tomoff's physiognomic cover diversity (PCD) model was 82 much more successful. Increasing the number of life form categories from four to ten gave even better results.
Calculating the cover diversity for each species (species cover diversity or SCD) gave the best results. The im portance of cover diversity is thought to be as an indi cator of foraging niche diversity, nest site diversity, food resource diversity, and as an index of the importance of each plant species. The number of plant species was highly correlated with bird species richness and bird species diversity, contrary to the findings of MacArthur.
Because of the "diversity" of diversity patterns found, it is suggested that future diversity studies should deal with entire communities or ecologically meaningful seg ments of communities (herbivores or insectivores, for example) rather than taxonomic segments of communities
(birds, mammals, and so on) .
The more diverse habitats exhibited less seasonal fluctuation in bird populations, lending additional support to the widespread idea that more diverse communities are more stable. APPENDIX I
FORMULAE OF SPECIES DIVERSITY INDICES AS USED BY THE
ORIGINAL AUTHORS, SHOWING MODIFICATIONS MADE IN THIS
PAPER IN THE INTEREST OF CONSISTENT USE OF SYMBOLS3
aSymbols used are as follows:
S = number of species N = total number of individuals n. = number of individuals of the ith species p^ = n./Nf the proportion of the ith species in the sample R. = rcEnk of the ith species if the species are ranked from most abundant to least abundant y = the importance value of the ith species I = N
83 Index Author Original Form Modification
AS Odum, et al., 1960 AS 1. Alog I Alog N
j _ S-l 2. Margalef, 1957, 1958 none £n N
n. n. Shannon and Weaver, 1949 H' = -Epi £n pi 3. H' = ^0<^bN~~
4. Brillouin,1956 H log none ~ N Ni:N2!..N^!
a _ Sn(n-l) Simpson, 1949 5. * " N(N-l) none
n. 2 Whittaker, 1965 c = 1^)
Levins, 1966 I = 2Pi2 none
MacArthur, 1972 Ds = -i-s- none Epi Index Author Original Form Modification
6. Mcintosh, 1967 d = /Tn~' none
_ N (S+l) _ 7. Fager, 1972 NM = none ZRi ni
N, N-N. n. N-n. 8. Hurlbert, 1971 4i - Esr fer) Ai = hr (srr1)
N „ 2X N < i v 2« (1 E7T N-i " i > N-l ^1_^pi ^
9. Tramer, 1969 j. = a; none ,max H APPENDIX II
RESULTS OF BIRD CENSUSES AT THE
FIVE STUDY SITES BY MONTHS
Numbers given for each species are the total indi
viduals seen during three censuses for that month.
Species Feb Mar May June July Oct Dec
SITE 1
Marsh Hawk - - - 1
White-winged Dove - 2 - -
Mourning Dove 2 9 2 1 6 1 -
Roadrunner - - - - 1 - -
Gila Woodpecker - - 2
Say's Phoebe - - - - - 1
Verdin - 1 - 5 6 11
Cactus Wren 14 4 3 8 1 -
Curve-billed Thrasher 3 2 1 1 1 -
Sage Thrasher 1 - -
Black-tailed Gnatcatcher 2 - - 2 5 11
Loggerhead Shrike - - - 2
Audubon's Warbler - - - 19
Pyrrhuloxia - 1 - - -
House Finch 262 6 - 4 2 2 -
86 87
Species Feb Mar May June July Oct Dec
SITE 1 (cont'd,)
Lark Bunting 23 - -
Brewer's Sparrow 24 157 4 - 3 -
Sage Sparrow - - 11
Black-throated Sparrow - 6 6 8 2
White-crowned Sparrow 15 19 - - - -
Total Individuals 333 199 10 22 39 22 25
Species 9 8 3 7 10 11 6
SITE 2
Red-tailed Hawk - - 1 - - -
Sparrow Hawk - 1 - -
Gambel's Quail - 1 - - -
White-winged Dove - - 10 4 16 - -
Mourning Dove - 7 3 5 1 - -
Roadrunner - 3 1 -
Costa's Hummingbird - 1
Gilded Flicker 6 2 7 7 4 5 4
Gila Woodpecker - 1 4 2 1
Red-shafted Flicker 1 - -
Ash-throated Flycatcher - - 4 5 7
Purple Martin - - 1 -
Verdin - 4 5 29 19 8 3 88
Species Feb Mar May June July Oct Dec
SITE 2 (cont'd.)
Cactus Wren 5 8 23 30 21 19 3
Curve-billed Thrasher 3 3 4 14 6 5 -
Sage Thrasher 1 1 - - -
Black-tailed Gnatcatcher - 1 4 15 6 8 -
Loggerhead Shrike 2 1 6 - 1 2 1
Lucy's Warbler - 3 - -
Scott's Oriole - 3 - - - -
Brown-headed Cowbird - 8
Black-headed Grosbeak - 1 - - -
House Finch 33 1 18 -
Lark Sparrow - - - - - 1 -
Brewer's Sparrow 33 14 2 - 11 1
Sage Sparrow - - - 2
Black-throated Sparrow 2- 2 5 12 11 7
Song Sparrow 2 - -
Mockingbird - 2 -
Say's Phoebe - 1 - -
Total Individuals 55 42 76 151 113 92 22
Species 9 10 15 12 17 13 8 89
Species Feb Mar May June July Oct Dec
SITE 3
Sharp-shinned Hawk - 1 - - - 1
Red-tailed Kawk - - 1 -
White-winged Dove - 11 5 21 - -
Mourning Dove 6 14 1 1 1 - -
Roadrunner - 2 4 - -
Great Horned Owl - 1 - - - -
Costa's Hummingbird - - 1 - -
Gilded Flicker 11 11 9 13 1 6 2
Gila Woodpecker 2 5 19 8 8 5
Ladder-backed Woodpecker - 1 8 - 3 -
Ash-throated Flycatcher - 4 - 9 1 - -
Say's Phoebe 2 - _
Purple Martin - 1 -
Verdin 10 6 16 53 46 26 14
Bewick's Wren - - 1 -
Cactus Wren 9 14 17 23 29 13 -
Mockingbird - 1 - - 1
Curve-billed Thrasher 1 4 7 19 11 9 1
Sage Thrasher 1 - - - - -
Robin - 1 - -
Black-tailed Gnatcatcher 5 8 7 12 10 15 7 90
Species Feb Mar May June July Oct Dec
SITE 3 (cont'd.)
Ruby-crowned Kinglet 1 - -
Phainopepla 2 - 2
Loggerhead Shrike - 2 1 -
Starling - 1 - -
Lucy's Warbler - 1 - -
Audubon's Warbler - - - 2
Brown-headed Cowbird - - 510 10 -
Pyrrhuloxia - 7 1 - -
House Finch 6 4 4 12 4 22 -
Brown Towhee 4 1 1 -
Brewer's Sparrow 42 70 24 - - 13 33
Rufous-winged Sparrow - - - 2 -
Sage Sparrow 3 - -
Black-throated Sparrow 6 9 5 10 16 11 2
White-crowned Sparrow 6 33 -
Total Individuals 117 188 120 188 163 132 68
Species 17 17 17 18 14 14 10
SITE 4
Red-tailed Hawk 2 1 1
Harris Hawk - - - - 1 - -
Sparrow Hawk - 2 1 Species Feb Mar May June July Oct Dec
SITE 4 (cont'd.)
Gambel's Quail - 15 - 8 5 - 15
White-winged Dove - - 7 2 6 - -
Mourning Dove 4 14 5 2 1 - -
Roadrunner - 1 1 3 2 - -
Lesser Nighthawk - - 1 1 4 - -
Costa's Hummingbird - - 2 - - - -
Red-shafted Flicker - - - - 2 -
Gilded Flicker 7 15 18 14 9 11 4
Gila Woodpecker 14 15 25 29 9 12 12
Ladder-backed Woodpecker - 1 1 - - - -
Wied's Crested Flycatcher - - - 1 1 - -
Ash-throated Flycatcher - 6 10 1 1 - -
Purple Martin - - 3 7 19 - -
Verdin 12 14 21 71 29 25 19
Bewick's Wren ------1
Cactus Wren 33 25 54 36 57 25 14
Mockingbird ------1
Curve-billed Thrasher 17 22 44 31 26 27 2
Black-tailed Gnatcatcher 4 6 11 18 12 6 6
Ruby-crowned Kinglet - 1 - - - - 3
Phainopepla 1 - - - 4 1
Loggerhead Shrike - - 3 1 1 - 92
Species Feb Mar May June July Oct Dec
SITE 4 (cont'd.)
Starling - 1 -
Bell's Vireo - 2 - - -
Lucy's Warbler - 1 -
Audubon's Warbler - - - 1
Black-throated Gray Warbler - - - - 1 -
Wilson's Warbler - - 1 - - -
Scott's Oriole - 1 - -
Brown-headed Cowbird - 5 6 1 -
Pyrrhuloxia - 2 -
House Finch - 1 1 1 - 6 -
Brown Towhee 4 2 2 - 1 3
Brewer's Sparrow 71 54 13 - - 13 12
Rufous-winged Sparrow - 1 1
Black-throated Sparrow 9 2 47 20 26
White-crowned Sparrow - 5 - - - -
Total Individuals 178 198 233 237 235 153 121
Species 12 17 23 21 21 13 16
SITE 5
Turkey Vulture - 1 1 -
Red-tailed Hawk 3 4 3 - 12
Sparrow Hawk 1 11 1 11 93
Species Feb Mar May June July Oct Dec
SITE 5 (cont'd.)
Gambel's Quail 7 13 6 6 10 1 1
White-winged Dove - - 15 13 11 - -
Mourning Dove 12 9 11 12 7 - -
Roadrunner - 1 - - 2 - -
Costa's Hummingbird - - - - 1 - -
Gilded Flicker 15 17 20 19 14 10 11
Gila Woodpecker 6 29 45 53 51 26 29
Ladder-backed Woodpecker - 2 - 3 2 - -
Wied's Crested Flycatcher - - 5 3 2 - -
Ash-throated Flycatcher - 2 16 6 10 - -
Purple Martin - - 12 32 12 1 -
Verdin 11 10 36 66 69 30 27
1 Bewick s Wren ------1
Cactus Wren 37 42 85 75 89 68 29
Rock Wren - - - - 1 -
Mockingbird 2 - - - - - 3
Curve-billed Thrasher 19 16 27 40 22 40 17
Black-tailed Gnatcatcher 3 1 10 6 4 4 4
Ruby-crowned Kinglet ------2
Phainopepla 1 - 1 1 - 7 18
Loggerhead Shrike - - - 1 - - - Species Feb Mar May June July Oct Dec
SITE 5 (cont'd.)
Starling 2 ------
Hooded Oriole - - 1 - - - -
Scott's Oriole - 2 10 - 1 - -
Bullock's Oriole - - 3 - - - -
Brown-headed Cowbird - - 6 - 2 - -
Pyrrhuloxia 1 1 1 2 - - -
House Finch - 2 10 1 2 - -
Pine Siskin ------1
Brown Towhee 3 7 5 5 5 3 5
Brewer's Sparrow 101 167 3 - - 11 3
Black-throated Sparrow 58 2 2 - 14 49 26
Rufous-winged Sparrow - - - 2 2 1
White-crowned Sparrow - 1 - - - -
Total Individuals 281 328 335 348 333 253 180
Species 17 19 25 21 22 16 17 APPENDIX III
RESULTS OF RODENT TRAPPING
Numbers of individuals trapped per 150 trap nights at each site.
Study Site Species
JUNE 1972
Dipodomys merriami 7 23 16 18
Perognathus penicillatus 2 7- 22
Perognathus intermedius - 4
Perognathus baileyi - - - 1
Perognathus amplus 22 7 10 13
Onychomys torridus - 4
Neotoma albigula - 1
Perarayscus sp. - - - 1
Total Individuals 31 37 26 65
Species 3 3 2 8
OCTOBER 1972
Dipodomys merriami 19 23 22 26 24
Perognathus penicillatus 2 4 5 18 26
Perognathus intermedius - - 1 3
95 96
Study Site Species 1 2 3 4 5
OCTOBER 1972 (cont'd.)
Perognathus baileyi - - • - 2 2
Perognathus amplus - 2 2 11 4
Onychomys torridus - 2 - 5 2
Neotoma albigula - - - 1 1
Mus musculus - - - 1 -
Total Individuals 21 31 29 65 62
Species 2 4 3 8 7
aSite 4 not trapped during June. APPENDIX IV
RESULTS OF LIZARD CENSUSES EXPRESSED AS
INDIVIDUALS PER HECTARE
Study Site Species 1 2 3 4 5
Cnemidophorus tigris 1.55 3.10 3.34 6.66 9.31
Callosaurus draconoides .44 1.33 3.67 3.67 2.30
Dipsosaurus dorsalis .17 +a 1.00 .33 +
Phrynosoma solare .22 + + + +
Uta stansburiana + + + + +
Urosaurus ornatus + + .30 + .67
Crotaphytus wislizenii + - - +
Sceloporus magister - - - +
Heloderma suspectum - - + +
Coleonyx variegatus - - - - +
Total Individuals 2.38 4.43 8.31 10.66 12.38
aPlus sign indicates species known to be present on site but not recorded on census.
97 APPENDIX V
NUMBER OF ANT COLONIES (1.6 HA. TRANSECT)
AT EACH SITE
Study Site Species 1 2 3 4 5
Pheidole xerophila - 45 53 8 30
Veromessor pergandei 4 41 60 22 1
Novomessor cockerelli 3 13 26 16 24
Pogonoiuyrmex pima 3 41 4 3 7
Acromyrmex versicolor - 8 33 8 5
Solenopsis xyloni 6 31 7 5 +£
Forelius foatida 1 18 22 2 1
Myrmecocystus spp. 2 8 19 4 1
Pheidole prob. hyatti - 14 10 2 1
Dorymyrmex pyramicus 5 9 6 - 2
Pogonomyrmex barbatus - 18 1 - -
Crematogaster depilus - 5 - 4 2
Solenopsis S£. 2 - 4 - 4 1
Pogonomyriaex rugosus 2 1 - - 4
Pogonomyrmex californicus 2 - 2 1 +
Camponotus ochreatus - 2 1 - 2
Camponotus S£. 2 ** + +
98 99
Study Site Species 1 2 3 4 5
Pheidole prob. crassicornis - - - - -
Neivamyrmex nigrescens - - - - +
Pseudomyrmex pallida - - - - +
Xiphomyrmex desertorum - - - +
Iridomyrjnex pruinosura - - - - +
Total Colonies 28 258 244 80 80
Species Censused 9 15 13 13 14
Species Recorded 9 16 14 13 20
aPlus sign indicates species known to be present at site but not recorded on census. APPENDIX VI
FOLIAGE ARTHROPOD SAMPLING RESULTS f
SEPTEMBER 1972, BASED ON 1000 SWEEPS AT EACH SITE
Study Site Species grasshopper 1 4 3 2 82 grasshopper 2 3 6 3 4 grasshopper 3 1 1 2 grasshopper 4 1 grasshopper 5 3 1 grasshopper 6 1 Eremiacris acris 2 2 grasshopper 8 6 grasshopper 9 4 grasshopper 10 1 grasshopper 11 1 grasshopper 12 6 grasshopper 13 2 Aretheae gracilipes 1 Insara covilleae 1 2 1 1 Cycloptilium sp, 1 2 3 2 Parabacillus hesperus 5 1 4 Diapheromera sp. 1 Litaneura minor 1 Staqmomantis californicus 1 Yersinops sophronicum 2 1 Psocoptera sp. 1 2
100 101
Study Site Species
Thysanoptera sp. 2 6 2 3 Tingidae sp. 4 14 15 5 Phymatidae sp. 1 3 phymatid nymph 1 5 Reduviidae 1 1 1 1 Reduviidae 2 1 5 Reduviidae 3 1 Miridae 1 2 1 Miridae 2 3 6 7 7 Miridae 3 1 5 3 1 Miridae 4 2 2 7 Miridae 5 1 1 3 10 Miridae 6 1 1 2 5 Miridae 7 1 Miridae 8 3 4 Miridae 9 3 Phlegyas prob. annulicus 15 19 Lygaeidae sp. 3 1 Mozena sp. 1 Pentatomidae 1 1 Pentatamidae 2 1 Scutelleridae sp. 1 scutellerid? nymph 10 2 1 undet. Hemiptera nymph 1 54 10 174 undet. Hemiptera nymph 2 1 undet. Hemiptera nymph 3 2 leafhopper 1 3 5 16 6 leafhopper 2 46 3 14 4 102
Study Site Species 1 2 3 4q 5
leafhopper 3 - 1 1 - leafhopper 4 1 6 3 4
leafhopper 5 - 4 - -
leafhopper 6 - 12 5 20 56 leafhopper 7 13 10 14 17 1
leafhopper 8 - 1 - **
leafhopper 9 - 7 - - leafhopper 10 3 2 5 2 leafhopper 11 13 1 13 6 2 leafhopper 12 8 1 10 14
leafhopper 13 1 1 - - leafhopper 14 19 1 2 1
leafhopper 15 20 - 7 3
leafhopper 16 - - - 1
leafhopper 17 - - - 1
leafhopper 18 - 1 1
leafhopper 19 - - - 3
leafhopper 20 - - 3 1
leafhopper 21 1 - 1 1
leafhopper 22 - - 3 -
leafhopper 23 - - 37 -
leafhopper 24 - - 1 -
leafhopper 25 1 - 1 -
leafhopper 26 - - 1 -
leafhopper 27 - - 1 -
leafhopper 28 1 - - -
leafhopper 29 10 - - -
leafhopper 30 1 - - - b leafhopper a 2 103
Study Site Species 1 2 3 4 5 leafhopper b 4 leafhopper c 5 leafhopper d 18 leafhopper e 4 leafhopper f 4 leafhopper g 10 leafhopper h 13 leafhopper i 6 leafhopper j 1 leafhopper k 1 leafhopper 1 1 leafhopper m 1 leafhopper n 1 leafhopper o 1 leafhopper P 1 leafhopper q 1 leafhopper r 1 leafhopper s 1
Membracidae 1 - - - 1 - Membracidae 2 34 1 3 1 -
Membracidae nymph - - 1 - 1
Membracidae 3 1 1 - - -
Membracidae 4 1 - - - -
Membracidae 5 1 - - - -
Cixidae ? - - - - 1
Flatidae 7 3 1 - 3 Acanaloniidae 1 97 41 37 64 93
Acanaloniidae 2 - - - 1 - undet, Homoptera 1 - - - - 1 104
Study Site Species 12 3 4 5 undet. Homoptera 2 13 4 6 6 2 undet. Homoptera 3 - - - 1 undet. Homoptera 4 - 4 - 2 undet. Homoptera 5 - - 2 2 2 undet. Homoptera 6 nymph - 1 undet. Homoptera 7 nymph - 2 undet. Homoptera 8 - 2 - undet. Homoptera 9 4 - - Chrysopidae larva - 1113 Myrmeliontidae - 1 13 Pachybrachys wickhami - 11 Pachybrachys chaoticus - 14 3 Pachybrachys 3 - - 1 - 2 Pachybrachys 4 - 2 - Pachybrachys 5 - 1 - Pachybrachys 6 1 - - - - Pachybrachys 7 1 - - - 2 Pachybrachys 8 - - - - 1 Coscinoptera 1 - 1 2 6 Coscinoptera 2 - - - 2 Euryscopa sp. 1 - - 1 Exema sp. - - - 8 near Epitrix - 3 3 4 Chrysomelidae 1 2 1 - Chrysomelidae 2 1 - - - Chrysomelidae 3 1-14 7 Chrysomelidae 4 2 1 3 Chrysomelidae 5 - 1 - 1 Hippomelas caerula - 2 105
Study Site Species
Acmaeodera bivulnerata Bruchidae 1 Bruchidae 2 Bruchidae 3 1 Bruchidae 4 2 Dermestidae sp. Tricorynus sp. 2 Collops sp. 1 Tenebrionidae sp. Cleridae 2 1 1 Coccinellidae 1 1 1 1 Coccinellidae 2 1 2 Coccinellidae 3 2 1 2 2 1 Coccinellidae 4 1 1 1 Coccinellidae 5 1 Rhysodidae 7 Staphylinidae 1 Curculionidae 1 2 1 8 17 Curculionidae 2 2 2 3 3 Curculionidae 3 16 1 2 13 Curculionidae 4 1 1 1 Curculionidae 5 1 3 Curculionidae 6 Curculionidae 7 1 Curculionidae 8 1 Curculionidae 9 1 undet. Coleoptera microlepidoptera 1 1 microlepidoptera 2 1 106
Study Site Species 1 2 3 4 - 5 microlepidoptera 3 - - 1 4 1 microlepidoptera 4 - - - - 1
Drosophila 1 - - 2 1 3
Drosophila 2 - - 1 -
undet. Diptera 1 - 1 1 - -
undet, Diptera 2 - 4 1 1 -
undet. Diptera 3 - 2 - -
undet. Diptera 4 - - - - 3
undet. Diptera 5 - - - - 1
undet. Diptera 6 - - - 3 2
undet. Diptera 7 11 - 6 2 -
undet. Diptera 8 - 1 - - -
undet. Diptera 9 - 1 - -
Pogonomyrmex pima - 1 - - 2 Crematogaster sp. 7 16 31 3 18
Pheidole xerophila 1 - 21 28 18
Novomessor cockerelli - - - 1 -
Acromyrmex versicolor - - - - 1
Solenopsis xyloni - 3 3 - - Forelius foetida 26 12 17 13 6
Dorymyrmex pyramicus 3 - 2 - -
Myrmecocystus sp. 2 - - — —
Camponotus ochraceus - - - - 1
Camponotus 2 - - 3 - —
Mutillidae 1 - - - -
undet. Hymenoptera 1 8 1 4 1 -
undet. Hymenoptera 2 7 9 8 - -
undet, Hymenoptera 3 8 5 2 - 2
undet. Hymenoptera 4 5 1 3 5 -
undet. Hymenoptera 5 - 3 2 4 6 107
Study Site Species 1 2 3 4 5 undet. Hymenoptera 6 - 2 - 2 3 undet. Hymenoptera 7 1 1 - - - undet. Hymenoptera 8 - - 3 - undet. Hymenoptera 9 2 - 2 2 2 undet, Hymenoptera 10 9 - 8 9 7 undet. Hymenoptera 11 1 - 5 2 2 undet. Hymenoptera 12 8 - 12 3 2 undet. Hymenoptera 13 - - - 2 1 undet. Humenoptera 14 - - 1 2 - undet. Hymenoptera 15 - - - 1 1 undet. Humenoptera 16 - - - 2 - undet. Hymenoptera 17 - - - 1 1 undet. Hymenoptera 18 - - - 1 - undet. Hymenoptera 19 5 - 2 - - undet. Hymenoptera 20 - - 4 - 1 undet. Hymenoptera 21 - - 1 - 3 undet. Hymenoptera 22 - - 1 - - undet. Hymenoptera 23 1 - 1 - - undet, Hymenoptera 24 - - - 1 - undet. Hymenoptera 25 5 - - - 3 undet. Hymenoptera 26 - - - - 4 undet. Hymenoptera 27 - - - - 3 undet. Hymenoptera 28 - - - - 1
undet, Hymenoptera 29 - - - - 2
undet. Hymenoptera 30 - - - - 2 spider 1 28 16 28 21 37
spider 2 - 4 - 2 3
spider 3 - 1 - - -
spider 4 - 2 - - 1
spider 5 - 3 - - - 108
Study Site Species 1 2 3 -4*— 5
spider 6 - 3 9 4 1 spider 7 3 1 5 2 1 spider 8 - 1 - - 3 spider 9 - 1 1 - -
spider 10 - - 3 2 -
spider 11 - - 1 5 3
spider 12 1 - 2 -
spider 13 1 - 2 7 23
spider 14 - - - 1 -
spider 15 - - 1 -
spider 16 - - - 1 -
spider 17 - 2 2 - -
spider 18 - - 1 - -
spider 19 - - 1 - 1
Sassacus popenhoei - - 1 - 2
spider 21 - - 1 - -
spider 22 - - 1 - 5
spider 23 - - 1 - -
spider 24 1 - - - -
spider 25 2 - - -
spider 26 2 - - -
spider 27 1 - - - -
spider 28 - - - - 2
spider 29 - - - - 5
spider 30 - - - - 5
spider 31 - - - - 3
spider 32 - - - - 1
spider 33 - - - - 1
spider 34 - - - 3
spider 35 - - - - 1 109
Study Site 1 2 3 4^ 5 2 2 1 3 1 1 1 apacheanus 1 1 1 1 1 1 2 1 - 2 27 1 14 5 22 12 2 7 14 7 1 4 2 6 1 4 1 3 2 5 110
Study Site Species 1 2 3 4 5 larva 18 - - - - 10 larva 19 - - - - 1 larva 20 17 - - - - larva 21 - - 12 - - larva 22 - - - - 1 larva 23 - - 2 1 - larva 24 - - 1 - - pupa 1 - - - - 1 pupa 2 - — — — 2 pupa 3 - - — 1 pupa 4 — - - nm 1 pupa 5 — — — - 1 pupa 6 - - - 1 pupa 7 - - 1 - 1 unidentified insect — 2 — 1 —
Total Individuals 526 254 632 503a 1023
Individuals/100 sweeps 52.6 25.4 63.2 62.9 102.3
Total Species 70 76 135 117a 181
Biomass/100 sweeps (g.) .0994 .0650 .1911 .2029 .8868
H' 3.347 3.658 4.029 3.829 3.997
aBased on 800 rather than 1000 sweeps (2 subsamples lost). y_ Leafhoppers 1-30, except for 2, 6, 7, and 11, were lost before the site 5 sample was sorted necessitating a second series, a-s, for site 5. APPENDIX VII
PERENNIAL PLANTS: NUMBER OF INDIVIDUALS
FOUND ON TEN 0.1 HECTARE QUADRATS
Study Site Species 1 2 3 4 5
Acacia constricta - 21 1 55 64
Acacia Greggii - - - 2 -
Aplopappus spinulosus 1 - 1 2 1
Calliandra eriophyllum - - - 8 3
Celtis pallida - 2 - 2 14
Cerdicium microphyllum - 3 77 54 103
Cereus giganteus - 1 7 21 44
Cereus Greggii - - - 2 -
Condalia lycioides - 3 - - 1
Echinocereus Fendleri - 8 - 5 7
Ephedra trifurea - - 3 - 1 Ferocactus Wislizenii 2 4 4 16 12
Fouquieria splendens - - - 2 5 Franseria deltoidea 10 2476 369 3801 5752
Franseria duiuosa - 34 1931 - -
Franseria ambrosioides - 1 - 2 1
Hymenoclea pentalepis - 2 17 - 328
Janusia gracilis - - - 23 66
Jatropha cardiophylla - - - 8 55
Krameria Grayi - - 440 53 Larrea tridentata 598 402 556 382 94 Lycium Berlandieri 7 5 8
111 112
Study Site Species 1 2 3 4 5
Maitunillaria microcarpa - - 1 4 25 Muhlenbergia Porteri 1 25 146 98 445
Olneya tesota - 11 10 3 56
Opuntia arbuscula - 2 2 20 4
Opuntia fulgida - 4 2 38 50
Opuntia leptocaulis 2 1 - 39 58
Opuntia phaeacantha - - - 9 176 Opuntia spinosior 2 1 31 1 Opuntia versicolor 2 10 1 24 323
Phorodendron californicum 15 - 3 21 40
Prosopis juliflora 2 17 6 - -
Psilostrophe Cooperi - - - - 1
Zinnia puraila 3 — 57 5 12
Total Individuals 638 3035 3194 5118 7612
Species 11 21 19 27 32 APPENDIX VIII
LIFE FORMS OF PERENNIAL PLANT SPECIES USED
IN CALCULATING PCD VALUES
Categories Species 4a 10*
Acacia constricta Sp TS
Acacia Greggii Sp TS
Aplopappus spinulosus P dS
Atriplex canescens P TS
Calliandra eriophyllum P dS
Celtis pallida Sp TS
Cercidium microphyllvim Sp TT
Cereus giganteus Su Su
Cereus Greggii Su Su
Condalia lycioides Sp TS
Echinocexeus Fendleri Su Su
Ephedra trifurca Sp TS
Ferocactus Wislizenii Su Su
Fouquieria splendens Sp TT
Franseria ambrosioidea P sS
Franseria deltoidea P dS
Franseria dumosa P dS 113 114
Categories Species 4a iob
Aplopappus spinulosus P dS
Hymenoclea pentalepis P dS
Janusia gracilis P L
Jatropha cardiophylla P BS
Krameria Grayi P dS
Larrea tridentata ES ES
Lycium Berlandieri P TS
Mammillaria microcarpa Su Su
Muhlenbergia Porteri P G
Opuntia: 6 species Su Su
Olneya Tesota Sp TT
Phorodendron californicum P Ep
Prosopis juliflora Sp TT
Psilostrophe Cooperi p dS
Zinnia pumila p dS
aSp = spinescent shrubs; Su = stem succulent; Es = evergreen sclerophyll; P = "perennial". u TT = thorn tree; TS = thorn shrub; dS = dwarf shrub; BS = broad-leaved deciduous shrub; sS = semishrub; ES = evergreen sclerophyll; L = liana; Ep = epiphyte; G = graminoid; Su = stem succulent. APPENDIX IX
NUMBERS OF ANNUALS FROM 50 ONE-METER
SQUARE QUADRATS AT EACH SITE
Study Site Species la 2 3 4 5
SPRING ANNUALS
Amsinckia intermedia + 10 5 18 -
Astragalus sp. - - 45 -
Bowlesia incana - 14 - -
Calyptridium monandrum 2 10 - -
Chorizanthe rigida + - 1 - Cryptantha sp. 1 34 34 2 Daucus pusillus 1 12 14 75
Descurainia sp. 1 6 - 1 Eriastrum diffusum 13 29 11 36
Eriogonum sp. - 5 - - Eriophyllum lanosum 144 176 103 23
Erodium texanum + 143 20 -
Lepidium lasiocarpum + 41 - 3 2
Lesquerella Gordoni + - - -
Lotus humistratus - - - 5
Lotus tomentellus 101 24 18 -
Lupinus concinnus - 9 18 10
Monoptilon bellioides - - 12 -
Oenothera primiveris - 1 - - Pectocarya recurvata 546 310 175 49 Phacelia crenulata 6 2 2
115 116
Study Site
Species la 2 3 4 5
SPRING ANNUALS (cont'd.)
Phacelia distans - - - 1 Plantago insularis + 1790 71 15 19
Rafinesquia neomexicana - 14 1 -
Sphaeralcea Coulteri 132 27 - -
Thelypodiura lasiophyllum 1 - 1 1
unknown #1 - - - 2 Total Individuals 7000b 2783 896 491 227 Species 6 13 18 16 14
SUMMER SPECIES Allionia incarnata 6 3 1 2 23
Amaranthus fimbriatus - - 1 - 27 Aristida sp. 1 1 6 1 10
Astragalus sp.? - 16 6 - 29
Boerhaavia intermedia - - - - 18 Boerhaavia spicata 154 12 2 12 132 Boutaloua aristidoides 215 827 590 939 3027 Bouteloua barbata 174 17 86 140 41
Panicum sp. - ** - 1 2 Tidestromia lanuginosa 1 1 7 15 42
unknown #4 - - - - 22
unknown # 5 - 4 1 3 28
unknown #6 - - - - 2
unknown # 7 - - 123 - - Total Individuals 551 881 823 1113 3403 Species 6 8 10 8 13
a Part of data from site 1 lost.
^Estimated. LITERATURE CITED
American Ornithologist's Union. 1957. Check-list of North American birds. Fifth edition. Lord Baltimore Press, Baltimore. 691 p.
Austin, G. T. 1970. Breeding birds of desert riparian habitat in southern Nevada. The Condor 72: 431-436.
Benson, Lyman. 1969. The cacti of Arizona, third edition. University of Arizona Press, Tucson. 218 p.
Bowman, K. 0., K. Hutcheson, E. P. Odum, and L. R. Shenton. 1971. Comments on the distribution of indices of diversity. In: Patil, G. P., E. C. Pielou, and W. E. Waters (eds.). Statistical Ecology, vol. 3. Pennsylvania State University Press, University Park.
Brillouin, L. 1956. Science and information theory. Academic Press, New York.
Brown, W. H. 1939. Tucson Mountain, an Arizona basin range type. Geological Society of America Bulletin 50: 697-760.
Cockrum, E. L. 1964. Recent mammals of Arizona. In: Lowe, C. H., Jr. (ed.) The vertebrates of Arizona. University of Arizona Press, Tucson. 270 p.
Connell, J, H. and E. Orias. 1964. The ecological regula tion of species diversity. American Naturalist 98; 399-414.
Creighton, W. S. 1950. The ants of North America. Museum of Comparative Zoology Bulletin 104: 1-585.
Diamond, J. M. 1969. Avifaunal equilibria and species turnover rates on the channel islands of California. Proceedings of the National Academy of Sciences 64: 57-63.
Dobzhansky, T. 1950. Evolution in the tropics. American Scientist 38: 209-221. 117 118
Eberhardt, L. L. 1971. Record of preplanned and spon taneous discussion. In: Bowman, K. D., et al. (op. cit.).
Emlen, J. T. 1971. Population densities of birds derived from transect counts. Auk 88: 323-342.
Fager, E. W. 1972. Diversity: a sampling study. American Naturalist 106: 293-310.
Felger, R. S. and C. H. Lowe. 1970. New combinations for plant taxa in northwestern Mexico and south western United States. Journal of the Arizona Academy of Sciences 6: 82-84.
Fischer, A. G. 1960. Latitudinal variations in organic diversity. Evolution 14: 64-81.
Fisher, R. A., A. S. Corbet, and C. B. Williams. 1943. The relation between the number of species and the number of individuals in a random sample of an animal population. Journal of Animal Ecology 12: 42-58.
Gilbert, E. N. 1966. Information theory after 18 years. Science 152: 320-326.
Gleason, H. A. 1922. On the relation between species and area. Ecology 3: 156-162.
Grassle, J. F. 1967. Influence of environmental variation on species diversity in benthic communities on the continental shelf and slope. Ph. D. disserta tion, Duke University, Durham, N. C.
Greig-Smith, P. 1964. Quantitative plant ecology, second edition. Butterworths, London. 256 p.
Hairston,N. G. 1959. Species abundance and community organization. Ecology 40; 404-416.
Hairston, N. G. 1964. Studies on the organization of animal communities. Jubilee Symposium Suppliment, Journal of Ecology 52: 227-239.
Hill, M. D. 1973. Diversity and evenness: a unifying notation and its consequences. Ecology 54: 427- 432. 119
Hutcheson, K. 1970. A test for comparing diversities based on the Shannon formula. Journal of Theo retical Biology 29: 151-154.
Hurlbert, S. 1971. The non-concept of species diversity: a critique and alternative parameters. Ecology 52: 577-586.
Johnson, M. P., L. G. Mason and P. H. Raven. 1968. Ecological parameters and plant species diversity. American Naturalist 102: 297-306.
Karr, J. R. 1968. Habitat and avian diversity on strip- mined land in east-central Illinois. The Condor 70; 348-357.
Kearney, T. H. and R. H. Peebles. 1964. Arizona Flora, second edition. University of California Press, Berkeley. 1085 p.
Klopfer, P. H. 1959. Environmental determinants of faunal diversity. American Naturalist 93: 337-342.
Klopfer, P. H. 1969. Habitats and territories. A study of the use of space by animals. Basic Books, New York. 117 p.
Kohn, A. J. 1967. Environmental complexity and species diversity in the gastropod genus Conus on Indo- West Pacific reef platforms. American Naturalist 101: 251-259.
Levins, R. 1966. The strategy of model building in ecology. American Scientist 54: 421-431.
Lloyd, .M. and R. J. Ghelardi. 1964. A table for calculating the "equitability" component of species diversity. Journal of Animal Ecology 33: 217-225.
MacArthur, R. H. 1955. Fluctuations of animal populations, and a measure of community stability. Ecology 36: 533-536.
MacArthur, R. H. 1957. On the relative abundance of bird species. Proceedings of the National Academy of Sciences 43: 293-295.
MacArthur, R. H. 1964. Environmental factors affecting bird species diversity. American Naturalist 97: 387-397. 120
MacArthur, R. H. 1965. Patterns of species diversity. Biological Reviews 40: 510-533.
MacArthur, R. H. 1972. Geographical ecology. Harper and Row, New York. 269 p.
MacArthur, R. H. and J. W. MacArthur. 1961, On bird species diversity. Ecology 42: 594-598.
MacArthur, R. H., J. W. MacArthur and J. Preer. 1962. On bird species diversity. II. Prediction of bird censuses from habitat measurements. American Naturalist 96: 167-174.
MacArthur, R. H. and E. D. Wilson. 1967. The theory of island biogeography. Princeton University Press, Princeton, N. J. 203 p.
Margalef, R. 1957. La teoria de la informacion en ecologia. Memorias de la Real Academia de Ciencias y Artes de Barcelona 23: 373-449.
Margalef, D. R. 1958. Information theory in ecology (translated from Spanish by W. Hall). General Systems 3: 36-71.
Margalef, D. R. 19 69. Diversity and stability: a practical proposal and a model of interdependence, p. 25-37. In: Woodwell, G. M. and H. H. Smith (eds.) Diversity and stability in ecological systems. Brookhaven Symposia in Biology, number 22. 264 p.
Mayo, E. B. 1968. A history of geologic investigation in the Tucson Mountains, Pima County, Arizona. Arizona Geologic Society, Southern Arizona Guide book III, p. 155-170.
Mayo, E. B. 1971. Defense of "volcanic orogeny." Arizona Geologic Society Digest 9: 39-60.
Mcintosh, R. P. 1967. An index of diversity and the rela tion of certain concepts to diversity. Ecology 48: 392-404. 121
Odum, H. T., J. E. Cantlon and L. S. Kornicker. 1960. An organizational hierarchy postulate for the interpretation of species individual distributions, species entropy, ecosystem evolution and the meaning of a species variety index. Ecology 41: 395-399.
Orians, G. H. 1969. The number of bird species in some tropical forests. Ecology 50: 783-801.
Paine, R. T. 1966. Food web complexity and species diversity. American Naturalist 100: 65-75.
Pianka, E. R. 1966. Latitudinal gradients in species diversity. American Naturalist 100: 33-46.
Pianka, E. R. 1967. On lizard species diversity: North American flatland deserts. Ecology 48: 333-351.
Pianka, E. R. 1970. Comparative autecology of the lizard Cnemidophorus tigris in different parts of its geographic range. Ecology 51: 703-720.
Pianka, E. R. 1971. Lizard species diversity in the Kalahari Desert. Ecology 52: 1024-1029.
Pielou, E. C. 1966a. Species-diversity and pattern- diversity in the study of ecological succession. Journal of Theoretical Biology 10; 370-383.
Pielou, E. C. 1966b. The measurement of diversity in different types of biological collections. Journal of Theoretical Biology 13: 131-144.
Pielou, E. C. 1966c. Shannon's formula as a measurement of specific diversity: its use and misuse. American Naturalist 100: 463-465.
Power, D. M. 1972. Numbers of bird species on the California Islands. Evolution 26: 451-463.
Preston, F. W. 1948. The commonness and rarity of species. Ecology 29: 254-283.
Raitt, R. J. and R. L. Maze. 1968. Densities and species composition of breeding birds of a creosotebush community in southern New Mexico. The Condor 70: 193-205. 122
Sager, P. E. and A. D. Hasler. 1969. Species diversity in lacustrine phytoplankton. I. The components of the index of diversity from Shannon's formula. American Naturalist 103: 51-60.
Sanders, H. L. 1968. Marine benthic diversity: a com parative study. American Naturalist 102: 243-282.
Sanders, H. L. 1969. Benthic marine diversity and the stability-time hypothesis, p. 71-81. In: G. M. Woodwell and H. H. Smith (eds.) Diversity and stability in ecological systems. Brookhaven Symposia in Biology, number 22. 264 p.
Shannon, C. and W. Weaver. 1949. The mathematical theory of communication. University of Illinois Press, Urbana.
Simpson, E, H. 1949. .Measurement of diversity. Nature 163; 688.
Simpson, G. G. 1964. Species density of North American recent mammals. Systematic Zoology 13: 57-73,
Smith, H. V. 1945. The climate of Arizona. University of Arizona Agricultural Experiment Station Bulletin 197. 112 p.
Stebbins, R. C. 1966. A field guide to western reptiles and amphibians. Houghton Mifflin Co., Boston. 279 p.
Tomoff, C. S. 1971. Breeding bird diversity in the Sonoran Desert creosotebush association. Ph. D. dissertation, University of Arizona, Tucson. 48 p.
Tramer, E. J. 1969. Bird species diversity: components of Shannon's formula. Ecology 50: 927-929.
Whittaker, R. H. 1952. A study of summer foliage insect communities in the Great Smokey Mountains. Eco logical Monographs 22: 1-44.
Whittaker, R. H. 1960. Vegetation of the Siskiyou Moun tains, Oregon and California. Ecological Mono graphs 30: 279-338.
Whittaker, R. H. 1965. Dominance and diversity in land plant communities. Science 147: 250-260. 123
Whittaker, R. H. 1970. Communities and ecosystems. Macmillan, New York. 162 p.
Whittaker, R. H. 1972. Evolution and measurement of species diversity. Taxon, vol. 21, pp. 213-251.
Wilson, E. 0. 1969. The species equilibrium. In: Woodwell, G. M. and H. H. Smith (eds.) Diversity and stability in ecological systems, p. 38-47. Brookhaven Symposia in Biology, number 22. 264 p.
Yang, T. W. 1957. Vegetational, edaphic, and faunal correlations on the western slope of the Tucson Mountains and the adjoining Avra Valley. Ph. D. dissertation, University of Arizona, Tucson. 154 p.
Yang, T. W. and C. H. Lowe, Jr. 1956. Correlation of major vegetation climaxes with soil characteristics in the Sonoran Desert. Science 123: 542.
Yount, J. L. 1956. Factors that control species numbers in Silver Springs, Florida. Limnology and Oceanog raphy 1: 286-295.