BEHAVIOUR OF ADULT NATIVE SKIPPERS, THEMISTOCLES

(Latreille, 1824), LN THE PRESENCE OF AN INTRODUCED ,

THYMELICUS LnVEOLA (Ochsenheimer, 1808)

A Thesis

Presented to

The Faculty of Graduate Studies

of

The University of Guelph

by

ANTHONY JAMES DREW

In partial fulfillment of requirements

for the degree of

Master of Science

My, 1999

O Anthony James Drew, 1999 National Libraiy Bibliothèque nationale 1*1 of Canada du Canada Acquisitions and Acquisitions et Bibliographic Services services bibliographiques 395 Wellington Street 395. me Wdlington OnawaOlY KlAôN4 KlAW canada canada

The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Library of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or seli reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la fome de rnicrofiche/flimyde reproduction sur papier ou sur format électronique.

The author retaùis ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts Fom it Ni la thèse ni des extraits substantiels may be printed or othewise de celle-ci ne doivent être imprimés reproduced without the author' s ou autrement reproduits sans son permission. autorisation. CHANGES IN BEHAVIOUR %Y A NATIVE , POLITES

THEMISTOCLES (Latreille, 18241, IN THE PWSENCE OF AN INTRODUCED

SPECIES, LRVEOLA (Ochsenheimer, 1808)

Anthony James Drew Advisor: University of Guelph, 1999 Professor E.G. Boulding

This thesis studied behaviour of skippers (: Hesperiidae) using observations fiom walking transects at sites in the Arboretum on the University of

Guelph campus. During the surnmers of 1997 and 1998, the behaviour of native skippers, , changed significantly in the presence of the introduced

European skipper, Thymelicus Iineola. The European skipper's behaviour also differed significantly in the presence of the native skipper. Changes in feeding behaviour suggested competition. These findings contrast some earlier work suggesting that biotic interactions, namely competition, are not important in some communities. Acknowledgments

1 would like to thank my supervisor, Dr. Boulding, for al1 her help, support and unexpected supervision of another graduate student. My advisory cornmittee was very helpfil and Dr. Nudds, in particular, contributed significantly to the final work. My partner in crime, Rebecca Vincent, also deserves special mention for continuous advice and commiseration. My wife was instrumental in helping me to finish this thesis, fiom putting up with late nights to re-reading without complaint section afier section and version after version. Last, but not least, my thanks go to Dr. David Gaskin, my original supervisor who gave me the opportunity and formed so rnuch of the base of the thesis.

In memory of Dave Gaskin Table of Contents

Ac know ledgments...... i

List of Tables...... iv

List of Figures ...... v

Introduction...... 1 Skippers...... 2 ... Biotic interactions ...... 4 Approach to research and hypotheses and predictions ...... 7 . . Statistical hypotheses...... 8

Materials and Methods...... II Study sites...... 1 Transects...... 12 ...,. Data analysis...... ,...... 13

Results...... 15 Abundance...... 15 ... Distribution...... 15 ... Relative distribution ...... 15 Between year behaviour ...... 16 Between site behaviour...... -16 Within site behaviour-skippers...... 17 Within site behaviour-conspecifics...... 18 Discussion ...... 20 Competition Abundance ...... 1 Distribution ...... 2 1 Between site behaviour...... 23 ... Within site behaviour...... 25 . . . . Conservation implications...... -28 Conclusions...... -32

References...... 34

Tables and Figures ...... 39

iii List of Tables

'able 1. Statistical hypotheses for determining if skipper cornpetition influences density, distribution, or behaviour of conspecifics or other species of skippers ...... 39

Table 2. Relative abundance of plant species at RJ Hilton Centre site in the University of Guelph arboretum, summer 1998...... -40

Table 3. Relative abundance of plant species at Stone RoaWictoria Road site in the University of Guelph arboretum, summer 1998 ...... 4 1

Table 4. Behaviour definitions used for generation of behaviour budgets for between site and within site behaviour comparisons...... 42

Table 5. Transect sampling dates and times for RJ Hilton Centre site and Stone RoadNictona Road site in 1997 and 1998...... 43

Table 6. Goodness of fit test for Poisson distribution of skippers and nnglet at the RJ Hilton Centre site and Stone RoaWictoria Road site...... 44

Table 7. Pearson correlation coefficients for skipper's and ringlet's distributions relative to each other (r values) at the RJ Hilton Centre site and Stone RoadNictoria Road site...... 45

Table 8. P values from within site cornparison of skipper and nnglet behaviour alone compared to in the presence of conspecifics and in the presence of other species at the Stone RoaWictoria Road site...... 46

Table 9. Sample transect data sheet for recording behaviour of buttedies at the Stone RoadNictoria Road site...... 47 List of Figures

Figure 1. Range and years and points of introduction of the European skipper, Thymelicus lineola, in Canada...... -.....48

Figure 2. Location of RJ Hilton Centre site and Stone RoadNictoria Road site in theUniversity of Guelph arboretum...... -49

Figure 3. Distribution of plants on 15 Transects at RJ Hilton Centre site in the University of Guelph arboretum, summer 1998...... -50

Figure 4. Distribution of plants on 6 Transects at Stone RoadNictoria Road site in the University of Guelph arboretum, surnmer 1998.. ..-5 1

Figure 5. Distribution of European skipper, Thyrnelicus lineola. on 15 transects at the RI Hilton Centre site in the University of Guelph arboretum, summer 1997...... 52

Figure 6. Total behaviour budget of European skipper, Thymelicus lineola, at RJ Hilton Centre site and Stone RoadNictoria Road site in the University of Guelph arboretum, summer 1997 and Stone Road/Victoria Road site, surnrner 1998...... 53

Figure 7. Total behaviour budget of the tawny-edged skipper, Polites themistocles, at RJ Hilton Centre site and Stone RoadNictoria Road site in University of Guelph Arboretum, summer 1997 and Stone RoadNictoria Road site, summer 1998 ...... 54

Figure 8. Total behaviour budget of the ringlet, Coenonympha tuflia, at the RJ Hilton Centre site and Stone RoadNictoria Road site in the University of Guelph arboretum, summer 1997 and Stone RoadNictoria Road site, surnmer 1998 ...... 35

Figure 9. Variation in behaviour budget of the European skipper, Thymelicus lineola, in the presence or absence of the tawny-edged skipper, Polites themistocles, and ringlet, Coenonynipha tulfia at the Stone RoadNictoria Road site in the University of Guelph arboretum, surnrner 1998...... 56 Figure 10. Variation in behaviour budget of the tawny-edged skipper, Polites themistocles. in the presence or absence of the European skipper, Thymelicus fineola at the Stone RoadNictoria Road site in the University of Guelph arbore-, sumrner 1998...... 57

Figure 1 1. Variation in behaviour budget of the ringlet, Coenonympha tuilia. in the presence or absence of the European skipper, 7%ymeficuslineola, and tawny-edged skipper, Polites themistocles, at the Stone Road/Victoria Road site in the University of Guelph arboreturn, summer 1998 ...... 58

Figure 12. Within site variation in behaviour budget of the European skipper, Thymelicus fineola, in the presence or absence of a conspecific at the Stone Road/Victoria Road site in the University of Guelph arboretum, swnmer 1998...... 59

Figure 13. Within site variation in behaviour budget of the tawny edged skipper, Polites themistocles, in the presence or absence of a conspecific at the Stone RoadNictoria Road site in the University of Guelph arboretum, sumrner 1998 ...... 60

Figure 14. Within site variation in behaviour budget of the ringlet, Coenonympha. tufia, in the presence or absence of a conspecific at the RJ Hilton Centre site in the University of Guelph arboretum, surnmer 1997...... 6 I Introduction

Introduction of non-native species is a serious problem worldwide, involving a wide range of phyla. introduced species may cause extinction of native species directly through predation, cornpetition or introduction of parasites or diseases. The argentine ant, Iridomyrmex humilis. displaced a number of species in California (Cole et al. 1992, Human and Gordon 1996, Holway 1998); some North Arnerican bird species were affected by introduced species such as the house sparrow, Passer dornesticics, and starling, Sturnus vzilgaris, fiom Europe (Diamond and Case 1986); and when an exotic mosquito, Aedes albopictus, was introduced in areas of South Florida, it replaced the native species, Aedes aegypti (Juliano 1998). The influence of invaders or introduced species is not always obvious. There may be effects on native species without causing extinction or generating clear evidence of effects (Petren and Case 1996).

Even when successfully established, most introduced species do not have a significant effect on native fauna (Diamond and Case 1986, Hill and Lodge 1994).

However, since some introductions do have profound consequences, it is important to study species interactions that may have long terrn effects (Diamond and Case 1986, Hill and Lodge 1994, Holway 1998, Juliano 1998). Although the effects may be long lasting, the interactions causing the effects may only occur over short periods of time.

Successful establishment is relatively rare for ; approximately 30%, and the odds for lepidoptera are even lower at less than 1% (Lawton and Brown 1986).

Nevertheless, the European skipper, Thymelicus lineola (Ochsenheimer, 1 8O8), is established in Southem Ontario where it is numerous and widespread. Skppers

Grass skippers (sub fami 1y Hesperiinae) are typically small, orange-brown

butterfiies. Host plants are grasses and sedges and adults feed on a variety of flowers.

Male skippers usuaily adopt a perching strategy to seek females and ofien have a stigrna

(streak of scent scales) on the forewing to attract females (Scott 1986). Despite their

powerful flight, rarely fly long distances or migrate. The thick thorax on

skippers makes their wings seem smaller than rnost butterflies. Skippers have a

characteristic basking posture in which the forewings are only partly spread (about 45

degrees) and the hindwings are hilly spread. Skippers are also distinguishable from

moths and Papilionoidea, "true butterfiies", in that they have clubbed, asymmetrical

(bent) antennae (moth antennae are typically unclubbed and Papilionoidea symmettical).

The European skipper, Thymelicus lineola, is a small, unadomed orange-brown

skipper. The preferred host plant is Timothy, Phleum pratense, but othen are also used

(Layberry et al. 1998) European skippers are univoltine, flying fiom June to mid-July-

Males have a short stigma and patrol for females, unlike most skippers which use a

perching strategy (Scott 1986).

The tawny-edged skipper, Polites themistocles (Latreille, 1824), is native to

Southem Ontario. It is a small, dark brown skipper with unrnarked hindwings and a

bright orange patch on the forewing (Layberry et al. 1998). Hostplants include blue grass, , and panic grass, Panicum species. Males have a large black stigma and use a perching mate searching strategy. The species is univoltine and the flight period is early June to mid-July. The ringlet, Coenonympha tullia, is a member of the Nymphalid family. It is usually a light orange-brown in colour with eyespots on the wings. The colour and eyespots of the species are very variable, but locally it has one clear eyespot on the upper forewing and a darker hindwing with white markings. There are many potential hostplants, arnong them blue grass, Poa pratensis, and needlegrass, Stipa species

(Layberry et al. 1998) There are usually two flights in southern Ontario, June to early

July and rnid-August to mid-September (Scott 1986). The males have no stigma and patrol for females.

The rapid spread and extensive populations of the European skipper in Canada suggest potential for displacing native species of Hesperiodea. It was introduced to

Ontario about 19 10 (Figure 1) and was soon comrnon throughout southem Ontario. It spread quickly to southem Newfoundland and New Brunswick (Scott 1986), perhaps facilitated by the low rate of parasitism on the species (Laybeny et al. 1998, McNeil

1983). It is also found in central British Columbia as a result of a more recent introduction in 1960. There has since been another introduction in Victoria, British

Columbia and the European skipper is now distributed across southern British Columbia

(Jon Shephard, personal communication). The European skipper has reached Manitoba fiom Ontario (McKillop et al. 19921, and there are pockets of populations in Alberta,

Saskatchewan, and Northern Quebec (Layberry et al. 1998). Records show the rate of spread in Canada to be at least 25 km per year (Scott 1986).

The Toronto Entomologist's association consistently found the European skipper to be by far the most numerous in butterfly and skipper counts throughout southem

Ontario (July 6/96 Windsor, July 7/96 Durham region, July 13/96 Toronto centre, July 1/97 Metro Toronto, July 6/97 Durham region, July 12/97 Toronto centre). Layberry et al. (1998) noted that the species is "unbelievably abundant", often more numerous than a11 other species combined. Sabo (1996) observed swarms of skippers and subsequent mass die-offs in 1995 in Southern Ontario (e.g. about 8000 in a 10m x 30m area and well over 100 000 over a 4 km stretch of marsh and lane). Populations of this size, while aberrant, suggest the potential for effects on native species.

I investigated whether the introduced, estabiished Empean skipper, 2ïzymeiicu.s lineola, and a native species, the tawny-edged skipper, Polites themistocles, interacted to the degree that abundance or behaviour of one species was affected by the other. There is a lack of consensus among ecologists regarding the influence of species interactions, especially in insect comrnunities (Roughgarden and Diamond 1986). Fwthermore, for this skipper taxocene, the question may have conservation implications for the native species.

Biotic interactions

Species interactions, primarily competition, were traditionally seen as pivota1 in determining the number and type of in a community. Basic Malthusian theory, that far more organisms are born than can survive, suggests limited resources and thus competition. Volterra and Lotka used equations to mode1 interspecific competition

(Begon et al. 1990). Work by Hutchinson (1959) and MacArthur and Levins (1967) furthered the premise that competition was crucial in determining community stnicture.

However, other interactions, such as predation or parasitism, have been found to be more important than competition (Conne11 1975, Schroder and Rosenzweig 1975, Hairston

1980, Strong 1984, Seifert 1984, den Boer 1986, Gurevitch et al. 1992). For some communities there is debate as to whether species interactions are important at al1 (Wiens

1977, Comor and Simberloff 1979, Strong 1979, Wiens and Rotenberry 1979,

Rotenberry and Wiens 1980, Wiens 1984, Roughgarden and Diamond 1986, Taylor and

Aarssen 1990, Juliano 1998).

Wiens (1977) was arnong the first to express reservations about the importance of cornpetition in some situations. He stated that, in some comrnunities, competition occurred sporadically because resources were limited sporadically. In these communities abiotic factors should have stronger influences than biotic factors (Wiens 1984).

Other authors expanded on Wiens' misgivings regarding cornpetitive interactions.

Comor and Simberloff (l979) disputed the idea that, on islands, species' distributions are deterrnined by competition, and Roughgarden and Diamond (1986) stated that it is not obvious, a priori, that interactions have far reaching consequences on comrnunity structure. Plant ecologists, in particular, have been displeased with the traditional theory of species coexistence via competition and niche differentiation because many plants use very similar resources (Taylor and Aarssen 1990). Effects of interactions may be transient in undisturbed systems and diEcult to study (Juliano 1998). There is tittle doubt that interactions occur; ail species either prey on others or are prey, parasitize or are parasitized, compete, or are involved in mutualisrn (Roughgarden and Diamond

1986). The relevant questions are how important are interactions and in which communities are they significant?

For example, in short lived organisms or short life stages in a life cycle, such as the adult stage of most lepidopterans, biotic interactions may be insignificant because the organism does not live long enough to be affected. Smaller organisms may be more vulnerable tban large ones to abiotic effects like weather, with consequently sparser

populations that are less likely to be affected by competition (Conne11 1983).

Competition appears to be reduced or absent in many insect communities. Wild

Drosophila demonstrated cornpetitive release, but their aggregated distributions resulted

in CO-existencebecause contact with competitors was limited (Shorrocks et al. 1984,

Shorrocks and Rosewell 1987). Parasitoids and predators were very important in

reducing the density of some phytophagous insects well be!ow carrying capacity so that

resources were not limited (Strong 1984). On the other hand, nectivores, like skippers,

have been considered to use resources as carnivores rather than herbivores, and should

therefore compete because resources are in relatively short supply (Slobodkin et al.

1967).

The importance of interactions may Vary in different communities (Wiens 1984).

Therefore, many different types of cornrnunities need to be examined before

generalizations about the role of biotic interactions may be possible. 1 exarnined a

skipper taxocene for which the literature is ambiguous with respect to whether biotic

interactions are important. However, considering previous studies, some general predictions can be made about the study group. in their native habitat, skippers, because of their short life span, small size, and because populations of insects may be below saturation due to predation or parasites, might be predicted to not be strongly influenced by competition. However, the European skipper, ThymeIicus Zineola, does not seem heavily parasitized in North America (Pengally 1960, McNeil 1983, Layberry et al.

1998). It has also been suggested that skippers are not heavily preyed upon (Clench

1967). Without parasites or predators potentially limiting this species' population size, they may be more likely to be resource limited and subject to competition. The extremely dense populations noted by Sabo (1996) could lead to resource limitation; however, densities of that nature are rare.

Skippers are nectivores which Stobodkin et al. (1967) predicted to compete more than herbivores, but more recent reviews (Comell 1983, Schoener 1983, Gurevitch et al. 1992) did not generally support this. Gurevitch et al (1992) found (with minimal data) that for terrestrial , Siobodkin's prediction was supported. However, most butterflies feed in a very opportunistic fashion (Scott 1986), a characteristic that leads to reduced interactions (Wiens 1984). The ecological events that caused changes in population size of checkerspot butterflies, Euphydryas editha and E. chalcedona. are associated with larvae rather than adults (Ehrlich et al. 1980). If this holds for other butterfly species, then biotic interactions may not be significant for adult skippers.

Approach to research and hypotheses and predictions

Two sites were used; one site had only the European skipper and common ringlet,

Coenonympha tufia, in significant nurnbers (more than thirty observations over the flight season). The other had the European skipper, ringlet, and tawny-edged skipper, Polites themistocles, in substantial numbers. Thus, the sites can be cornpared as if the tawny- edged skipper were "added" to one site. If competition is significant among skippers then there should be significant changes in distribution, abundance, or behaviour when there is an additional species present. This cornparison is weak because of uncontrolled habitat differences, but within site cornparisons can help clan9 the effect of habitat variation between sites. For exarnple, assuming that interactions are scale invariant, comparing behaviour of a solitary butterfly to behaviour in the presence of other skippers within site removes effects of confounding factors between site, such as habitat differences. Thus, the research hypothesis reads: competition significantly influences adult skipper distribution, abundance, or behaviour. The altemate hypothesis is that competition does not significantly influence adult skipper distribution, abundance, or behaviour.

Statistical hypotheses

Predictions fiom the research hypothesis are shown as the statistical hypotheses tested (Table 1). Distribution and abundance are easy to measure and interactions influence these parameters (Tilman 1982, Elrnberg et al. 1997, Juliano 1998, Comell

1983, Schoener 1983, Peltzer et al. 1998). If competition is significant then the density of the European skipper will be lower at the site with the tawny-edged skipper present than at the site where the European skipper was the only skipper in significant numbers.

Non-random distribution is a necessary, if not sufflcient, piece of evidence when asserting presence of competition. Even if the species are distributed non-randomly, however, there are alternative explanations other than competition (habitat structure for example). Once non-random distribution is established, the butterflies distribution relative to each other forms the next filter. For example, a negative association between skipper distributions might suggest interspecific competition. Even if the species are randomly distributed with respect to each other, competition may still be important but may manifest subtly, such as via behaviour. For instance, if food is limited, the skippers may spend more time searching for food when there are other skippers present. Behaviour can be looked at separately for each species at each site and should change between sites if competition is important. Comparing between site behaviour is a broad cornparison. Controls are difficult because there are so many potential confounding factors between sites: habitat structure, food resources, and weather are a few potential differences that might affect behaviour. However, by doing the same cornparison

(solitary behaviour vs. behaviour in the presence of other species) wirhin sites, the potential confounds of different sites are eliminated.

Specifically, if behavioural change of a species between sites is due to presence/absence of specific species we might see similar changes in behaviour within sites in the presencefabsence of those other species. If the within site behaviour does not change, or changes in different ways, it suggests that the behaviour differences seen between sites rnay be due to other differences between the sites. Conversely, there may be no significant changes in behaviour between sites, but significant changes of within site behaviour in the presence or absence of certain species. This would suggest that interactions between those species are important but masked by habitat differences or other confounds when comparing behaviour between sites.

The importance of competition in many communities, particularly insect communities, has been questioned. To test the importance of competition, 1 searched for consistent patterns among the given hypotheses. Specifically, 1 examined changes in the traditional measures of distribution and abundance. Unlike most studies, 1 aho examined the buttedies on a subtle level, studying the changes in behaviour, both between and within sites. Support for any one of the statistical hypotheses alone, is not compelling evidence of competition between skippers. However, a consistent pattern of support of the hypotheses is a strong indication about the veracity of the research hypothesis, that cornpetition is important for skipper populations. Materials and Methods

Study sites The study was conducted fkom rnid-June to mid-August in 1997 and 1998 at the

University of Guelph Arboretum. The arboretum had numerous potential study sites and skippers such as Thymelicus lineola, Polites themistocles. P. peckius, P. mystic, vestris and Cartercephah pafeamon may be found there. The study sites (Figure 2) were fields southwest of the RI Hilton Centre, longitude 43' 32' 3 1.6" N, latitude 80" 13'

1 1.6" W (henceforth referred to as the "RJ Site", Figure 3) and southeast of the intersection of Stone Road and East Victoria Road, longitude 43" 32' 3 1.9" N, latitude

80" 13' 10.7" W (referred to as the "SV Site", Figure 4). Both sites were chosen because they were habitats suitable for skippers. The sites were reserve areas that had been undisturbed, at least five years for the RI site, and twenty years for the SV site (Alan

Watson, personal communication). With undisturbed sites, pesticide application, mowing, or other disruption was not a concem.

Percent cover of vegetation was determined by randomly sampling along transects with a 1 m x 1 m quadrat. The RJ site was a pss field, primarily timothy,

Phleum pratense. Flowers such as bird's foot trefoil, Lotus cornialatus. and field bindweed, Convovulvus awensis. were also common (Table 2). The field was north facing and bounded by tree lines to the north and east. The SV site was also a grass field but less dominated by timothy and had heavier growths of goldenrod and aster than the

RJ Site (Table 3). Bird's foot trefoil was abundant and Viper's bugloss, daisies, and in late sumrner Queen Anne's lace, were present in quantity. Although mostly open, this site had a few small deciduous and conifer trees. The SV site was at the top of a small hi11 and was bordered by trees on the South and East sides, road on the North and West sides. The two sites were separated by approximately 2 km.

Tmnsects

Transects were used to gather distribution and behaviour data. 1 sampled two sites with permanent transects which were walked daily, excepting weather conditions such as rain or extreme wind, fkom mid June to early August in 1997 and 1998. Tirne to walk al1 transects at a site varied from 15- 120 minutes, depending on butterfly density and weather. At the SV site, the area used was 100 m x 40 m with 6 permanent transects running west-east. Transects 1-5 were 95 m long, transect 6 was 80 m long, and there was 5 m between transects. At the RJ Hilton area, the study site was 1 10 m x 75 m. The area had 15 permanent transects running west-east. Transects 1-2 were 95 rn long and transects 3-15 were 105 m long. Transects were 5 rn apart. Permanent transects were used at both sites to attempt to minimize trampling of growth. Time of day waUUng the transects varied randomly (fkom between 0930- 1700 hours) to avoid bias in behaviour patterns restricted to certain times of day.

Behaviour, plant associated with behaviour (if any), and location on transect (by pace) of al1 bunerflies seen within 2.5 m on either side or in front of the observer were recorded (see table 9). For exarnple, on June 18, 1998 at the SV Site, on Transect 1 there was a European skipper feeding on bird's foot trefoil at Pace 5. European skippers were also seen at paces 32 and 94, a tawny-edged skipper was basking on goldenrod at Pace

33, and ringlets were flying at paces 6 1 and 104. Behaviours were categorized as feeding, flying, basking, perching, mating, or

spiral flight. Behaviour definitions were similar to the five categories used by Pivnick

and McNeil(1987), feeding, flying, basking, resting, and courtship. 1 used perching in

place of resting behaviour as it is a more appropriate definition than resting. I also

included spiral flight as a separate category given its probable role in temtoriality

(Davies 1978, Wickman and Wikiund 1983). If a butterfiy was disturbed by my

passage before behaviour was observed, it was not recorded. For behaviour definitions

see Table 4. The total time spent sampling transects was 3920 minutes, the dates and

times for which are listed in Table 5.

Diflerences in behaviour alone vs. in the presence of skippers or conspecifics

were compared. This was done between sites and wirhin a site. The definition of "alone"

and "in presence of' differed fiom presence or absence at the site to presence or absence

within a given distance within the site. For exarnple, the European skipper was the only

skipper in reasonable nurnbers (more than 30 sightings per season) at the RJ site so it was

considered "alone" at that site and behaviour at that site was compared to the SV site

where the European and tawny-edged skipper were present in reasonable numbers. For

within site comparisons, the definition of "alone" is "no other buttemies within 5 paces

of the observed butterfly".

Dala Analysis

Data analysis was done using Systat 5.03 for Windows or Microsoft Excel 5.0~.

Abundance of the European skipper was compared between sites with an independent t- test of the mean number of skippers per transect. Each site was divided into 24 quabts and skippers per quadrat was determined fiom transect data. A Poisson analysis was used to check for randomness of distribution for each species (Krebs 1989). Transect data were used for Pearson correlation indices of species distribution relative to each other.

Transect data from each site, each species, and each year generated a behaviour budget.

This budget was compared between species, yem and sites using contingency tables and log-linear models, reporting the log likelihood ratio chi-square and Pearson chi-square

(Agresti i 990). The behaviour of species alone and in the presence ofother species was compared within sites using contingency tables and log-linear models. Results

Abundance

During 1997 the abundance of the European skipper was significantly lower at the

SV (two species) site than the RJ site (three species site), Independent t-test, P=0.002.

There was not enough data from the RJ site in 1998 to compare the sites. The tawny- edged skipper was only present at the SV site, so cornparison between sites for that species was not possible.

Distribution

Al1 three species' distributions were non-random and showed a tendency to aggregation (Table 6). Both the European skipper and nnglet showed more aggregation at the RJ site than the SV site. Figure 5 shows the distribution of Ewopean skipper at the

FU site. The tawny-edged skipper was not present at the RJ site and had a clwnped distribution at the SV site.

Relative species distribution

The distributions of the three species were not significantly correlated with each other (Table 7). The only exception was July of 1998 when the distribution of the ringlet and European skipper were positively correlated at the SV Site (r =0.44, P =0.03). Behaviour between years

The behaviour budgets of the three species were compared between years and showed little annual variation at the SV site. The behaviour budget of the European skipper did not significantly change fiom 1997 to 1998 (Figure 6, x2=7. 1, des, P=0.2 13,

1997 n=166, 1998 n=302). There was not enough data from the RJ site in 1998 for comparison to the 1997 data. A between year comparison of behaviour budget showed no significant difference for the tawny-edged skipper at the SV site (Figure 7, ~G2.76, dF5, P=0.737, n=55 in 1997, n=175 in 1998). Between 1997 and 1998 there was no significant difference between the behaviour budgets of the ringlet (Figure 8) at the SV site (~~4.2,df3, P4.522, 1997 n=87, 1998 n=82)..

Behaviour between sites

The behaviour of the European skipper varied significantly between the two sites.

The behaviour budget of the European skipper is significantly different at the RJ site, with no other skippers, compared to that of the SV site, with the tawny-edged skipper present. (Figure 6, f= 14.2, df3, W.014, 1997 RJ site n=1053, 1997 SV site n=166).

Mating behaviour occurred at the same rate at each site. Flying was a farger part of behaviour at the SV site than the EU site. Basking, perching, feeding and spiral flights were al1 more prevalent at the RI site than the SV site.

The behaviour budget of the ringlet was not significantly different between the RJ site and the SV Site (Figure 8, x2=2.482, df%, P=0.779, 1997 RI n=252, 1997 SV n=87). The tawny-edged skipper did not occur at the RJ site, so a between site cornparison was not possible.

Behaviour within site-skippers

In 1998 the behaviour of both skipper species within site was significantly different in the absence of other skippers compared to theu presence. Table 8 summarizes within site cornparisons at the SV site. Within site, the European skipper's behaviow changed significantly in the presence or absence of a skipper (Figure 9, f= 15.4, dW, P=0.004, 1998 SV site n=242 absence, 1998 SV site n=48 presence of the tawny-edged skipper). The largest difference was in spiral flights which were more fiequent in the presence of the tawny-edged skipper than in its absence. Basking was more cornmon for the European skipper in the absence of the tawny-edged skipper than in its presence. The European skipper also perched more fiequently when alone then when in the presence of a skipper. Flying and feeding behaviours of the European skipper were virtually unchanged in the absence of skippers compared to in their presence.

For 1997 the behaviour of the European skipper was not significantly different in the presence of a skipper compared to their absence ( SV Site, x2=3.0, dW, P=O.S58, n= 141 in absence of skippers, n= 14 in the presence of the tawny-edged skipper, n= 1 1 in the presence of the ringlet. RI Site, ~12.4,d&5, W.672,n=896 in absence of skippers, n=157 in the presence of the ringlet). The tawny-edged skipper was not present at the RJ site. The tawny-edged skipper's behaviour also di ffered signi ficantly when alone compared to in the presence of a skipper in 1998 (Figure 10, ~L19.9,des, P=O.O 1, 1998 n=125 alone, 1998 n=48 in presence of the European skipper). Feeding behaviour was the most disparate, is was lower aïone than in the presence of the European skipper.

Perching was more common in the absence than in the presence of a skipper. The variation in other behaviours was minimal.

Like the European skipper, in 1997 the tawny-edged skipper's behaviour budget did not differ significantly in the presence or absence of a skipper within site (SV Site,

~L2.9,df%, P=0.582, n=35 in absence of the European skipper, n= 14 in presence of the

European skipper).

Within site, there was no significant difference between the behaviour of the ringlet alone and in the presence of the tawny-edged or European skipper. This was true for both sites, both years (Figure 11, 1998 SV site, ~L3.7,di%, P=0.598, n=54 absence of a skipper, n=28 in presence of a skipper. 1997 RI Site, ~L1.4,des, P=0.489, n=230 absence of a skipper, n=22 in presence of a skipper. 1997 SV site, f=4.2, des, P=0.376, n=6 1 absence of a skipper, n=17 in the presence of a skipper).

Behaviour within site-conspecifcs

Behaviour changes for the skippers were even more haticin the presence of conspecifiçs than in the presence of skippers. The European skipper's behaviour differed significantly when alone compared to when in the presence of another European skipper

(Figure 12, 1998 SV Site, x2=39.1, dH,P= 2 x IO-', n=198 alone, n=104 in presence of a conspecific). The largest difference was in flying behaviour, which was more fiequent if conspecifics were absent than present. Feeding and spiral flights were less common when alone. Mating behaviour could not be obsexved in a lone European skipper but was

3.9% of behaviour in the presence of a conspecific. Perching was more common when

European skippers were alone than when another European skipper was nearby. There was almost no difference in basking behaviour in the presence or absence of a conspecific.

The tawny-edged skipper aiso showed significant changes in behaviour budget in the presence of a conspecific relative to when it was alone (Figure 13, 1998 SV site,

X'=59.8, df%, b1.31 x n=125 in absence, n=50 in presence of conspecific). Spiral flights showed the largest difference and were mucb more fkequent in the presence of a conspecific than in the absence. Mating behaviour occurred solely in the presence of another tawny-edged skipper at a 10% fiequency. Feeding, flying, percbing, and basking, were al1 more common when alone then when in the presence of a conspecific.

The behaviour of the ringlet did not differ significantly in the presence of a conspecific at the SV site in 1998 (Table 8) but the sample nurnber was quite low. At the

RJ site in 1997 where the sarnple nurnber was higher, the behaviour of the ringlet also differed significantly when in the presence of a conspecific (Figure 14, 1997 EU site,

X2=3 1.4, des, F==û.78x 105, n=189 in absence, n=63 in presence of conspecific). Spiral flights and mating were completely absent in solitary ringlets whereas feeding and basking were never observed in the presence of a conspecific. Fiying and perching behaviours were similarly comrnon in the presence or absence of a conspecific. Discussion

My results support the hypothesis that competition significantly influences skippers, but the effects are dernonstrated in behaviour rather than in distributiori or abundance. This contrasts with some previous studies that: a) suggested competition is not an important influence on community structure, especially for insects; and b) only exarnined changes in distribution and abundance, not behaviour, when studying competition. Cornpetition is not likely a cause for conservation concern for the native tawny-edged skipper in the presence of the introduced European skipper, as originally suspected, because intraspecific competition for the Euopean skipper appears to be stronger than interspecific competition. The native skipper shows increased feeding effort in the presence of the European skipper as does the nurnerically superior European skipper in the presence of conspecifics. The cornpetitive effects of conspecifics on the

European skipper will likely mitigate eflfècts of interspecific competition on the native tawny-edged skipper. This may allow the native species to CO-existin most habitats, probably at a lower equilibnum population size than before the European skipper was present. However, if the interspecific competition becomes stronger relative to the intraspecific competition, there may be an increased risk of extinction for the native species. Competition

Abundance

My first prediction stated that if the skippers were competing, then their abundance or density would Vary when species diversity was different between sites. In particular, a decrease in abundance of the native tawny-edged skipper in the presence of the introduced European skipper compared to its absence would be an indicator of exploitation competition. This comparison was not possible since 1 was unable to find sites with the tawny-edged skipper but without the European skipper present. However, comparison of abundance cm be made for the European skipper in the presence vs. absence of the native species. The density of the European skipper did decrease significantly at the SV site with the native species present compared to the RJ site where the European skipper was the only skipper in substantial nurnbers. This may indicate competition between the species, but the lack of controls between sites limits the strength of these data. The fluctuation could be due to habitat differences or other factors.

Without compelling evidence to support or reject the research hypothesis using the above measure of abundance, distribution was exarnined.

Distribution

My second prediction focused on whether or not skippers were distributed randomly. Al1 three species were non-randomly distributed and aggregated. Non- randornness is a very broad filter to check for the presence of competition between the species since interactions influence distribution. Competition is not the only cause of a non-random distribution. For example, the similar distributions of the European skipper and nectar sources at my RJ site suggest that the former is attributable to the latter. A non-randorn, aggregated distribution is consistent with previous work on skippers, such as the chequered skipper, Carterocephuluspafaemon (Ravenscroft 1994). Testing for a non-random distribution is tautological for most organisms; thus my third hypothesis considered correlations between the distributions of the skippers.

The third prediction was that competition would result in a correlation, likely negative, between the distribution of the species. Pairwise cornparison of the distributions of the species revealed no correlation, positive or negative, between any of the species at either site. The only exception was one period at the SV site when a positive correlation between the distribution of the ringlet and European skipper was found. However, given the absence of correlation between these species at any other time or site, this was probably a Type 1 error.

The lack of correlation fond suggests that competition is not important among skippers, since this interaction typically affects abundance andor distribution (Tilman

1982, Elmberg et al. 1997, Juliano 1998, Conne11 1983, Schoener 1983, Peltzer et al.

1998). in particular, when species distributions are aggregated and independent of each other, interspecific competition may occur but it is not considered a significant factor because contact between cornpetitors is limited (Shorrocks et al. 1984, Shorrocks and

Rosewell 1987). If interspecific competition is Iow, then intraspecific cornpetition will increase. However, if a limited resource is aggregated and species distribution show a positive correlation, then exclusion of the weaker cornpetitor becomes more likely than when distributions are independent (Shorrocks and Rosewell 1987). The RJ site bad aggregated food resourçes, so interspecific competition between skippers may be prominent there. Intraspecific competition may be more conspicuous than interspecific at the SV site where nectar sources were patchily distributed.

Since the conventional measures yielded little evidence of significant competition between the European skipper and native species, it could be tempting to stop searching, especially considering that interactions were not predicted for some other cornmunities

(Wiens 1977, Wiens 1984). For example, in avian communities, even though interactions may be occurring, they could not be detected because of abiotic factors obscuring relationships, or because resources were rarely limiting (Wiens and

Rotenberry 1979). More recent work has observed similar situations in other communities, particularl y small, r-selected type organisms, such as insects. Strong

(1984) observed that Hispine beetles hctioned in a density-independent manner and did not compete due to parasitoids and environmental stochasticity maintaining the population at a low level. However, since European skippers are not heavily parasitized, they may be more subject to resource limitation than the aforementioned groups.

Furthermore, examination of individual behaviour was found to be crucial in understanding trophic interactions (Schmitz and Booth 1997). Evidence of competition may be found in the behaviour of the skippers.

Between site behaviour

The fourth prediction was that the behaviour of the introduced European skipper at a site without the native skipper would be significantly different compared to one with the native skipper present. It would have been preferable to examine the behaviour of the native species when solitary compared to sites with the European skipper present. However, this comparison was impossible as no sites were found without the European

skipper. The European sEpper's behaviour did change significantly at a site where the

native tawny-edged skipper was present compared to a site where it was absent. The

biggest change was an increase in flying behaviour by the European skipper at the site

where the native skipper was present. Perching, feeding, and basking behaviour al1

decreased in the presence of the native skipper.

Cornpetition for nectar between the tawny-edged skipper and European skipper

might have resulted in increased search time for food, which could be reflected in an

increase in flying behaviour, leaving less time for perching and basking. However, if this

was the case, feeding behaviour (which is really a measure of feeding effort since actual

feeding, i.e. nectar uptake via proboscis, cannot be observed) should have also increased.

AItematively, the perching mate-searching strategy of the native species may have

caused a relative increase in flying behaviour of the European skipper. The tawny-edged

skipper perches and flies out at passing butterflies to search for receptive females (Scott

1986). Ravenscrofi (1 994) noted that male chequered skippers responded to male

intruders by increasing their flight time. Thus, the mate-location response of the tawny-

edged skipper could explain the increase in flying time, but if so, one would expect an

increase in spiral flights, a temtorial behaviour associated with perching mate-location strategy, which was not seen. The differences observed in the between site behaviour comparison could also be attributed to factors such as habitat structure, since sites were not identical. The within site behaviour comparison can compensate for confounding site differences and leads to the fifih prediction, that within site behaviour of solitary skippers will be significantly different than behaviour in the presence of other butterflies. Within site behaviour

During the 1998 season, within site behaviour was significantly different for

solitary skippers compared to those in the presence of other skippers. The behaviour did

not differ significantfy in 1997, but sample numbers were very low and the behaviour

budgets did change sirnilarly to the patterns seen in 1998. A butterfiy was considered

"solitary" within site if it was at least 5 paces away from any other butterfly. The tawny-

edged skipper showed significant changes in behaviour, notably a large increase in

feeding betiaviour and decrease in perching behaviour, in the presence of the European

skipper. An increase in feeding behaviour in tbis situation might suggest a lack of

competition for food because of previous competition resulting in niche differentiation,

the cIassic "ghost of competition past" (Connell 1980). However, feeding behaviour is

really a measure of feeding effort so, according to optimal foraging theory, the increased

feeding suggests that the European skipper and tawny-edged skipper do compete for food

(Bautista et al. 1998). The tawny-edged skipper may spend more time feeding in the

presence of the European skipper because the latter is utilizing the same nectar sources.

The possibility of competition for food among skippers has been suggested in the

literature. Clench (1 967) observed temporal dissociation in the flight periods of eleven

skippers and argued that the cause was adaptation to avoid competition for nectar. Since

these data were observational, it is only suggestive of competition since there are a number of alternative explanations (host plant requirements, thennoregulatory needs, etc.) for the differing flight periods. Demonstrating that one species negatively affects resource consumption by another is crucial to show exploitation competition (Petren and

Case 1996).

increased spiral flights and decreased basking were the largest changes in behaviour for the European skipper when in the presence of the tawny-edged skipper.

The increase in spiral flights was not unexpected, given the perching mate searching strategy of the tawny-edged skipper that disposes it to temtorial behaviour (Ravenscroft

1994, Demis and Williams 1987). If the European skipper and tawny-edged skipper competed for food, then the European skipper's behaviour in the presence of the tawny- edged skipper should have altered similarly to that of the tawny-edged skipper in the presence of the European skipper, with increased feeding behaviour. 1 did observe increased feeding behaviour, although not dramatically as for the native species in the presence of the European skipper. The numerical superiority of the European skipper compared to the tawny-edged skipper probably results in a lesser effect fiom exploitation competition. Interspecific competition is typically asymmetnc (Begon et al. 1990).

As expected, the behaviour of both skipper species does not change significantly in the presence of the common ringlet, a non-skipper (Nyrnphalidae), nor does the behaviour of the ringlet change significantly in the presence of skippers. Substantial differences exist between the ringlet and skipper; the nnglet has a much larger winghody ratio than skippers, flies much slower, and requires less energy so it feeds infiequently.

The fact that skippers ignore the presence of a dissirnilar species and change behaviour in the presence of other skippers supports the possibility of a cornpetitive relationship. The significant changes in behaviour demonstrate that competition between the two species are important despite, suggestions in the literature that biotic interactions may not be a significant force in shaping some communities, particularly for insects (Strong 1984, Wiens and Rotenberxy 1979, Wiens 1984, Shorrocks et al. 1984,

Shorrocks and Rosewell 1987, Eimberg et al. 1997). These results are consistent with the traditional idea that biotic interactions are important in shaping many communities. Luo and Fox (1996) stated that any interpretation of community patterns must take into account the direct effects of interspecific interactions. In particular, they noted the importance of food as the limiting resource for which most animals compte, and they obse~eda change of food resowce use in a mouse when a rat species was removed fiom experimental sites.

Intraspecific competition was also found to be significant in this study. In both years the behaviour of both skipper species and the ringlet changed significantly in the presence of conspecifics compared to solitary behaviour within a site. The tawny-edged skipper had a massive increase in spiral flights in the presence of conspecifics. This is expected since the behaviour is associated with their mate searching behaviour which is territorial (Ravenscroft 1994). The huge increase in the spiral flights resulted in a decrease in the kequency of al1 other behaviours in the presence of conspecifics. The increase in spiral flights masked any other changes in behaviour that may have occurred for the tawny-edged skipper. The European skipper's behaviour in the presence of conspecifics changed much like that of the tawny-edged skipper in the presence of the

European skipper, with a large increase in feeding. This increased feeding effort again is likely the result of competition for food, intraspecific in this case rather than interspecific. Conservation impkations of cornpettition

Zt is worth noting that the degree of behavioural change in the presence of conspecifics was greater than in the presence of other species. Thus, the intraspecific competition is stronger than the interspeci fic competition, in accordance with most previous studies. There was evidence of significant interactions between the European skipper and native species, both direct efKects (fiom spiral flights) and indirect effects

(nectar utilization by the ubiquitous European skipper correlated with increased feeding behaviour in the tawny-edged skipper). However, these interactions do not necessarily affect the population of native tawny-edged skipper detrimentally.

The behaviour changes of the native skipper in the presence of the European skipper suggests a potential cornpetitive effect which, due to the abundance and range of the European skipper, could be deleterious to the native species. However, the behavioural changes of the European skipper in the presence of conspecifics are more pronounced than the changes in behaviour by the European skipper in the presence of the tawny-edged skipper or by the tawny-edged skipper in the presence of the European skipper. Both species had an aggregated distribution that was independent of other species, a situation that mitigates interspecific competition because of decreased contact between species and increases intraspecific competition (Shorrocks and Rosewell 1987).

The strong intraspecific competition of the European skipper may "compensate" for the interspecific competition between the ubiquitous European skipper and relatively uncommon tawny-edged skipper. I believe that native skippers are not in significant danger of extinction or displacement, despite the wide range and large population of the European skipper, because of the balance between the intraspecific and interspecific competition. The interspecific competition is probably harmfiil to both species and the large population sizes of the European skipper would suggest that they would absorb any losses much better than the tawny-edged skipper. However, the intraspecific competition of the

European skipper is strong enough that the interspecific competition does not impact on the populations as strongly as it would if the intraspecific eRects were absent. This is a well recognized phenornenon, modeled by the classic Lotka-Volterra equations (Begon et al. 1990). Their mode1 is represented by two equations:

and

N is population size, r is intrinsic rate of increase, K is carrying capacity, and a is a competition coefficient. For exampie a,,measures the per capita cornpetitive effect on species I of species 2. A value of a,,41 means that species 2 has less effect on species 1 than other members of species 1, i.e. that intraspecific competition is stronger than interspecific competition. If this is the case for both species then they approach a stable equilibrium combination at a srnaller population size than if alone.

Strong intraspecific interactions relative to interspecific interactions are also consistent with recent literature. Intraspecific cornpetitive effects among herbivore groups were larger than interspecific effecl (Gurevitch et al. 1992). Intraspecific competition was stronger than interspecific in 75% of studies on competition (Comell

1983). Treves and Chapman (1 996) also found evidence that conspecific interactions were a driving force in comrnunity stnictwe. They examined predation pressure, resource defense, and conspecific threat and found that conspecific threat had the strongest effect on group size and composition. However, their results are not consistent with al1 previous work, namely that which suggests that biotic interactions, particularly among insects, are not important (Kareiva 1982, Strong 1984, Shorrocks et al. 1984,

Shorrocks and Rosewell 1987). Predators andfor parasitoids often reduce phytophagous insect populations below densities tha: would foster competition (Strong 1984). For a variety of reasons many species do not reach high enough population densities to result in significant competition (Strong 1984). In the case of the skipper taxocene studied here, this seems not to be tme, at least for the European skipper.

Clench (1967) addressed the possibility of predation accounting for patterns in skippers that he interpreted as evidence of competition for food. He stated that predators are infiequent for butterflies and did not occur at a high level in tems of population dynamics. Furthemore, predation will rarely prevent competition as this requires special types of predators that prey upon whichever prey is more abundant (Abrams 1986).

Population densities high enough to observe significant behaviod interactions between

the skippers also may occur because of the lack of parasitism on the European by native

parasitesfparasitoids. This is unusual given that introduced species are usualI y more

vulnerable to native parasites and such enemies are often the cause of failure to establish

for insect species (Lawton and Brown 1986). The success of the Euopean skipper is also

surprising given that probability of successfiil establishment bas been correiated with

body size; therefore insects are less likely to succeed than most other organisms, and, of

al1 insects, lepidoptera were found to be the least likely to establish populations(lawton

and Brown 1986).

introduced species might be more vuinerable to competition because of lack of

adaptation, but studies of introduced species have not borne this out (Strong 1984).

There are likely to be effects of direct cornpetitors on species trying to enter a new

community and there is no reason to believe this process is any more or less important

than predation (Lawton and Brown 1986). Two mosquitoes, the introduced Aedes albopictus and the established Aedes aegypti, competed for food resources and A. afbopictus was usually the superior competitor (Juliano 1998). Cornpetition resulted in displacement in some habitats but not others, possibly because the detrimental effects of

invaders on residents occurred only in areas that were marginally suitable for residents

(Juliano 1998).

One feature that might marginalize a habitat for some species is clurnping of resources. Petren and Case (1996) found that interspecific competition for food in lizards was much more intense and the cornpetitive advantage of one species exacerbated when food resources were clurnped. Given the interspecific competition between the

European and tawny-edged skipper this is a possible explanation for the absence of the

tawny-edged skipper at the RJ site. The RJ site seems perfectly suited to the tawny-

edged skipper with wide open grassy fields and the required host plants such as Poa

pratensis (Scott 1986). However, the nectar sources are strongly aggregated at the EU

site, unlike the SV site where the tawny-edged skipper is quite abundant. The diffise

food resources at the SV site may be a mitigating factor that helped the tawny-edged

skipper avoid displacement from the European skipper, but at the Ri site where food

resources are very clumped, exploitation competition may have ken too intense for the

tawny-edged skipper. The clurnped resources at the RI site may have resulted in a

positive correlation in the distribution of the European skipper and any native skippers,

which would have caused a higher degree of association between them, allowing the

superior cornpetitor to displace the weaker one (Shorrocks et al. 1984, Shorrocks and

Rosewell 1987)-

Conclusions

My work shows that significant behavioural interactions occurred between the introduced European skipper, Thymelicus lineola, and a native skipper, Poiites themzklocles. These interactions include direct and indirect effects and suggest competition between the skippers. These findings contrast with those of previous workers who suggest that competition may not be important in stnicturing some communities, in particular, small, r-selected organisms such as most insects. In addition to observing distribution and abundance, this study also examines behaviourd changes in detail to test for competition. Despite the competition between the ubiquitous introduced skipper and comparably rare native skipper, the native skipper is probably not in danger of displacement or extinction in most habitats because intraspecific competition in the introduced skipper is much stronger than the interspecific competition. I believe this creates an equilibrium in which the native skipper population is maintained, albeit at a reduced level compared to before the Euopean skipper was introduced. The tawny- edged skipper may be vulnerable to displacement in areas with clumped food resources where interspecific competition is more intense. References

Abrams, P.A. 1986. The competitive exclusion principle: other views and a reply, Trends in Ecology and Evolution 1: 13 1- 132. New York, NY.

Agresti, A. 1990. Categorical Data Analysis. John Wiley & Sons, Inc.

Begon, M., Harper, J.L. and Townsend, C.R 1990. Ecology : Individuals, Populations and Communities. Blackwell Scientific Publications, Cambridge, MA. Pp. 240- 279,

Bautista, L.M., Tinbergen, J., Wiersma, P., and Kacelnik, A. 1998. Optimal foraging and beyond: how starlings cope with changes in food availability. American Naturalist 152: 543-554.

Clench, H.K. 1967. Temporal dissociation and population regulation in certain Hesperiine butterflies. Ecology 48: 1000- 1006.

Cole, F.R., Madeiros, A.C., Loope, L.L., and Zuelke, W.W. 1992. Eflects of the Argentine ant on arthropod fauna of Hawaiian high-elevation shrubland. Ecology 73: 1313-1318.

Connell, J.H. 1975. Some mechanisms producing structure in natural communities: a mode1 and evidence from field experiments. Ln: Cody, M.L. and Diamond, J.M. (eds.) Ecology and Evolution of Communities, Harvard University Press, Cambridge, Mass., pp. 460-490.

Connell, J.H. 1980. Diversity and the coevolution of cornpetitors, or the ghost of competition past. Oikos 35: 13 1- 143.

Comell, J. H. 1983. On the prevalence and relative importance of interspecific competition: evidence fiom field experiments. American Naturalist 122: 661- 696.

Connor, E.F. and Simberloff, D. 1979. The assembly of species communities: chance or competition? Ecoloa 60: 1 132- 1 140.

Davies, N.B. 1978. Territorial defense in the speckled wood butterfiy (Pararge aegeria): the resident always wins. Behaviour 26: 138- 145. den Boer, J.P. 1986. The present status of the competitive exclusion pnnciple. Trendr in Ecology and Evolution 1: 25-28. Demis, R. L. H. and Williams, W. R 1987. Mate location behaviour of the large skipper butterfly, Ochfodes venata: flexible strategies and spatial components. Journal of the Lepidopteran Society 41: 45-53.

Diamond, J. and Case, T.J. 1986. Overview: Introductions, extinctions, and invasions. In: Diamond, J. and Case, T.J. (eds.) Communify Ecology, Harper & Row, New York, New York, pp. 65-79.

Ehrlich P.R., Murphy, D.D., Singer, M.C., Sherwood, C.B.,White, RR., and Brown, 1.L. 1980. Extinction, reduction, stability and increase: the responses of checkerspot butterfly (Euphydryas) populations to the California drought. Oecologia 46: 10 1- 105.

Elmberg, J., Poysa, H., Sjoberg, K., and Nummi, P. 1997. Interspecific interactions and CO-existencein dabbling ducks: observations and an experiment. Oecologia 111: 129-139.

Gurevitch, J., Morrow, L., Wallace, A., and Waish, J. 1992. A meta-analysis of competition in field experiments. American Naturalist 140: 539-572.

Hairston, N.G. 1980. Species packing in the salamander Desmugnathi*~:what are the interspecific interactions invoived? American Naturalist 115: 354-366.

Hill, A.M. and Lodge, D.M. 1994. Die1 changes in resource demand: competition and predation in species replacement among crayfishes. Ecologv 75: 2 1 18-2 12 1.

Holl, K.D. 1995. Nectar resources and their influence on butterfly communities on reclaimed coal surface mines. Restoration Ecology 3: 76-85.

Holway, D.A. 1998. Effect of Argentine ant invasions on ground-dwelling arthropods in northem Califomia riparian woodlands. Oecologici 116: 252-256.

Human, K.G. and Gordon, D.M. 1996. Exploitation and interference competition between the invasive Argentine ant, Linepthema hurnile, and native ant species. Oecologia 105: 405-4 1 2.

Hutchinson, G.E. 1959. Homage to Santa Rosalia, or why are there so many kinds of animals? American Naturalist 93: 145- 159.

Juliano, S.A. 1998. Species introduction and replacement among mosquitoes: interspecific resource competition or apparent competition? Ecologv 79: 255-264.

Karieva, P.K. 1982. Exclusion experiments and the competitive release of insects feeding on collards. EcoZogy 63: 696-702. Krebs, C. J. 1989. Ecological Methodology. Harper Collins Publishers, Inc., New York, NY.

Lawton, J. H. and Brown, K.C. 1986. The population and ecology of hvading insects. Phil. Trans. R. Soc. Lond 314: 307-6 17

Laybeny, RA., Hall, P.W., and Lafontaine, J.D. 1998. The Butterjlies of Canada. University of Toronto Press, Toronto, ON.

Luo, J. and Fox, B.J. 1996. Cornpetitive effects of Rattus lutreolus presence on food resource use by Pseudomys gracilicaudatus. Australion Journal of Ecology 20: 556-563.

MacArthur, R.H. and Levins, R. 1967. The limiting similarity, convergence and divergence of coexisting species. American Naturalist 101: 377-385.

McKillop, W.B, Preston, WB., and Westwood, A.R. 1992. Range extension for the European skipper, Thymeliw lineola (Ochsenheimer, 1808) (Lepidoptera: Hesperiidae), in Manitoba. Canadian EntomologLri 178: 943-944.

McNeil, J.N. 1983. Thymelicus lineola (Ochs.), European Skipper (Lepidoptera: Hesperiidae). In: Kel lerher, J.S. and Hulme, M.A. (eds.). Biological Confrol Programmes Against Insects and Weeds in Canada, 1969-1980. Cornmonw. inst. Biol. Control Tech. Commun. Series No. 8. Pp. 79-83.

Peltzer, D.A., Wilson, S.D., and Geny, A. 1998. Competition intensity along a productivity gradient in a low diversity grassland. American Nuturalist 151: 465- 471.

Pengally, D.H. 1960. Thyntelicus lineola (Ochs.) (Lepidoptera: Hesperidae), a Pest of hay and Pasture grasses in southem Ontario. Proceedings of the Entornologial Society of Ontario 9 1 : 189- 197.

Petren, K. and Case, T.J. 1996. An experimentd demonstration of exploitation competition in an ongoing invasion. Ecology 77: 1 18- 129.

Pivnick, K.A. and McNeil, J.N. 1987. Die1 patterns of activity of Thymelicus lineola adults (Lepidoptera: Hesperiidae) in relation to weather. Ecological Entornology 12: 197-207.

Ravenscroft, N.O.M. 1994. Environmental influences on mate location in male chequered skipper buttedies, Carterocephaluspalaemon(Lepidoptera: Hesperiidae). Animal Behaviour 47: 11 79- 1 186. Rotenberry, J.A. and Wiens, LA. 1980. Habitat structure, patchiness, and avian cornmunities in North American steppe vegetation: a multivariate analysis. Ecology 61: 1228- 125 1

Roughgarden, J. and Diamond, J. 1986. Overview: the role of species interactions in community ecology. Ln: Diamond, J. and Case, T.J. (eds.) Community Ecology, Harper & Row, New York, New York, pp. 333-344.

Sabo, T. 1996. Swarms of European Skippers. Toronto EntomologiSts Association 2%: 6-8.

Schoener, T.W. 1983. Field experirnents on interspecific compe2tion. American Naturalist 122: 240-285.

Schmitz, O.J. and Booth, G. 1997. Modelling food web complexity: The consequences of individual-based, spatially explicit behavioural ecology on trophic interactions. Evohtionary Eco logy 11: 379-398.

Schroder, G.D. and Rosenzweig, M.L. 1975. Perturbation analysis of cornpetiton and overlap in habitat utilization between Dipodmys ordii and Dipodomys meMami. Oecologia 19: 9-28.

Scott, J.A. 1986. The butterflies of North Arnenca. Stanford University Press, Stanford, California.

Seifert, R.P. 1984. Does competition structure comrnunities? Field studies on neotropical Heliconia insect communities. In: Abele, L.G., Simberloff, D.S., Strong, D.R., and Thistle, A.B. (eds). Ecological Communities. Princeton University Press, Princeton, New Jersey. Pp. 439-458.

Shorrocks, B., Rosewell, J. and Edwards, K. 1984. Interspecific cornpetition is not a major organizing force in rnany insect comrnunities. Nature 310: 3 10-3 12.

Shorrocks, B. and Rosewell, J. 1987. Spatial patchiness and community structure: coestistence and guild size of drosophilids on ephemeral resources. In; Gee, J.H.R. and Giller, P.S. (eds) Organization of Communities: Past and Present. Pages 29-52.

Slobodkin, L.B., Smith, F.E., and Hairston, N.G. 1967. Regulation in terrestrial ecosystems and the implied balance of nature. American Naturalist 101: 109- 124.

Strong, D.R. 1979. Biogeographical dynamics of insect-host plant communities. Annual Review of Enromology 24: 89- 1 19. Strong, D.R. Jr. 1984. Exorcising the ghost of competition past: phytophagous insects. In: Abele, L.G., Simberloff, D.S.,Strong, D.R., and Thistle, A.B. (eds). Ecologica l Communities. Princeton University kss, Princeton, New Jersey. Pp. 28-42.

Taylor, D.R. and Aarssen, L. W. 1990. Complex competitive relationships among genotypes of three perennial grasses: implications for species coexistance. American Naturalist 136: 305-327.

Tilman, D. 1982. Resource Competition and Community Structure. Monographs in Population Biology 17. Princeton University Press, Princeton, New Jersey.

Treves, A. and Chapman, C.A. 1996. Conspecific threat, predation avoidance, and resowce defense: implications for grouping in langurs. Behavioural Ecology and Sociobiology 39: 43-55.

Wickman, P-O. and Wiklund, C. 1983. Temtonal defense and its seasonal decline in the speckled wood butterfly (Pararge aegeriu). Animal Behaviour 31 : 1206.

Wiens, J.A. 1977. On competition and variable environrnents. Amencan Science 65: 590-597.

Wiens, J.A. 1984. On understanding a non-equilibriurn world: myth and reality in community patterns and pro ces ses.^: Abele, L.G., Simberloff, D.S., Strong, D.R., and Thistle, A.B. (eds). Ecologrcal Cornmunifies. Princeton University Press, Princeton, New Jersey. Pp. 439-458.

Wiens, J.A. and Rotenberry, J.T. 1979. Diet niche relationships among North American grassland and shrubsteppe birds. Oecologiu 42: 253-292. Table 1. Statistical hypotheses for determinimg if skipper cornpetition influences density, distribution, or behaviour of conspecifics or other species of skippers.

1. Ho:European skipper density is not significantly different between a site with no other skippers and a site with other skipper species. HA:European skipper density is significantly different between a site witb no other skippers and a site with other skipper species.

2. Ho: Skippers are distributed randomly throughout a site. HA:Skippers are distributed non randomly throughout a site.

3. Ho: Skippers are distributed randûmly with respect to each other. HA: Skippers are distributed non randomly with respect to each other.

4. Ho:European skipper behaviour is not significantly different between a site with no other skippers and a site with other skipper species. HA:European skipper behaviour is significantly different between a site with no other skippers and a site with other skipper species.

5. Ho:Skipper behaviour is not significantly different in the presence or absence of other species within a site. HA:Skipper behaviour is significantly different in the presence or absence of other species within a site.

6. Ho: Skipper behaviour is not significantly different in the presence or absence of conspecifics within a site. HA: Skipper behaviour is significantly different in the presence or absence of conspecifics within a site. Table 2. Relative abundance of plant species at RJ HiIton Centre site in University of Guelph arboretum, sumrner 1998.

scientific narne comon name abundance (% cover determined using random sampling with 1m x 1m quadrat)

Phleum pratense timothy 40% Bromus inermis smooth brome 11% Dactylis glornerata orchard grass 10% P oa pratensis Kentucky bluegrass 10% Lotzls comicrr/atus bird's foot trefoil 8% Soldiga gigan tea giant goldenrod 6% Agrostis alba redtop 4% Soldiga grarnin ryolia goldenrod 3% Virgulus novae angliae New England aster 3% Asclepias syr-iaca rnikveed 2% Echirrm vulgare Viper's bugloss 1% or less L inaria vulgaris butter and eggs 1% or less Trifoliurn pratense red clover 1% or less Con vovulvus arvensis field bindweed 1% or less Hypericum perforatrrnz St. John's wort 1% or less Dazrcus carota Queen Anne's lace 1% or less Tararacum officinale dandelion 1% or less Festuca rubra fescue 1% or less Table 3. Relative abundance of plant species at Stone Road/Victoria Road site in the University of Guelph arboretum, summer 1998.

scientific name cornmon name abundance (% cover determined using random sampiing with 1m x 1m quadrat)

Sddiga gigantea giant goldenrod 12% Dacylis glomerafa orchard grass 1 1Yo Poa prarensis Kentucky bluegrass 10% Lotus corniczrlatus bird's foot trefoil 10% YirguZus novae angliae New England aster IO% Daucus carota Queen Anne's lace 7% Agrostis alba redtop 5% Phleirm pratense timothy 5% Soldrga graminifolia goldenrod 5% Centaurea cJ jacea brown knapweed 5% Aster lanceolatzrs panicled aster 4% Bellis perennis daisy 3% Piantago lanceolara common plantain 3% Echitrm vulgare Viper's bugloss 2% Linaria vulgaris butter and eggs 2% Asclepias syriaca miIhveed 2% Con vo vulws arvensis field bindweed 1% or less Tararacurn oflcinale dandel ion 1% or less Trifolium pratense red clover 1% or less Pmnelia vtrfgaris heal al1 1% or less Centaureajacea brown knapweed 1% or less Table 4. Behaviour defiinitions used for generation of behaviour budgets for between site and within site behaviour comparisons.

Feeding - skippers on nectar sources were assumed to be feeding unless it was obvious that they were not (Le. proboscis clearly not visible, unable to reach nectar). This may have resulted in overestimation of feeding behaviour (Ho11 1995). If feeding was observed, the nectar source was recorded.

Perching - Skippers stationary on the ground or a plant with wings folded Le. that were not feeding or basking.

Basking - Wings set in characteristic basking position of skippers (hindwïngs fully spread, forewings spread at 45 degrees) when alighted on a plant or the ground.

Flying - Basically level flight with no spiraling.

Spiral Flight - Flying in tight, spiral, usually upward (with another butterfly or skipper).

Mating Behaviour - One skipper landing on, or attempting to land on another skipper, one skipper trying to mate with another while perched, or skippers locked in intercourse,

Table 7. Pairwise Pearson correlation coefficients for skipper's and ringlet's distributions relative to each other (r values) at the RI Hilton Centre (RI) site and Stone RoadNictoria Road (SV) sife in the University of Guelph arboretum, summer 1997 and 1998.

Site Year Month N Species 2

Thymelicus Polites Species 1 lineola thernistocles

June 26 Thymelicus lineola -

16 Polites thenzistocles -0.2 16

57 Coenonympha tullia 0.108

July 140 Thynlelicus lineola -

39 Polites themistocles -0.0 13

30 Coenonympha tullia 0.162

June 270 Thymelicus lineola -

129 Polites themistocles 0.069

17 Coenonyrnpha itrllia 0.442'

Juiy 32 Thymeliczts lineola -

46 Polites themistocles 0.2 1 5

35 Coenonynlpka tullia -0.057

June+ 105 Thyrnelicus lineola - JuIy 3

252 Coenonympha iullia 0.236

* - significant at < 0.05

.- P. themistocles not at RJ site, correlation not possible Table 8. P values from contingency table anaiysis of within site cornparison of skipper and ringlet behaviour alone compared to in the presence of conspecifics and in the presence of other species at the Stone RoacVVictoria Road site in the University of Guelph arboretum, summer 1998 (sample number in brackets Le. N alone, N in presence of).

Test Species

Focal Species

European skipper tawny-edged skipper ringlet

European 2.1 x 1 O-'*** 0.004** (198, 104) (242,48) tawny-edged 0.01 1" 1.3x10-~*** skipper (125,48) (125,SO) ringlet Table 9. Sample transect data sheet for recording behaviour of butterflies at the Stone RoaWictoria Road site in the University of Guelph arboretum, summer 1998.

- - - Date: June 18 Weather: Sumy Temperature: 25°C

Species Tl # Beh Pla T2 # Beh Pia T3 # Beh Pfa

Thymeliczrs lineola 5 fe Ic 19 f 1 fe lc 32 f 3 fe lc 94 ba sgi 11 f 19 fe dsy 66 P ?Pd

Polites thenzistocles 3 3 ba sgi 24 p bi 15

Coenonympha tullia 6 1 f f 104 f fe dsy f

ba - basking Beh - behaviour dsy - daisy (Bellis perennis) f - flying fe - feeding # - nurnber of butterfiies seen Ic - Lotus corniculatus p - perching Pla - plant associated with behaviour (if any) sgi - Solidago gigmtea Tl - transect 1 Figure 1. Range (shaded) and years and points of introduction of the European skipper, Thymclicus lineulrr, in Canada. i + 6&= s-- *-- . --- 4- art- * - - a fi- -u; :---&*-;.- =-A - .a ,. . 9.. **- *-: -. .: n . - . - * Y"@-. -f&-$

- i"!%J .m[<.l.\\'.b~.lI["; ) 3Hg? 3 B..... B..... B..... Figure 3. Distribution of plants on 15 Transects at RJ H ilton Centre Site in University of Guelph arboretum, summer 199 S.

Legend I I 0 field bindweed 1 viperLsbugioss w bird's foot trçfoil 1 1 rmlkweed 11 II St. John's wort U - deciduous tree goldcnrod Figure 4. Distribution of plants on 6 Transeets at Stone RoacWictoria Road site in the University of Guelph arboretum, summer 1998.

.egend C9 daisy

0 trefoil

7 goldenrod

de ciduous Figure 5. Distribution of European skipper, Thymeiicus lineoia, on 15 transects at the RJ Hilton Centre site in the University of Guelph arboretum, summer 1997 (N=602). Figure 6. Total behaviour budget of European skipper, Tlymeiicus lineoia, at RI Hiiton Centre (RI) site and Stone Road/Victoria Road (SV) site in University of Guelph arboretum, summer 1997 and SV site, summer 1998.

1 jm~sita~;; I. I. SV site '97 i

SV site98 1 j

rrating feeding fiying spiral basking perching Bs haviour Figure 7. Total behaviour budget of the tawny-edged skipper, Polites themistocles, at the Stone Road/Victoria Road (SV) site in University of Guelph arboretum, summer 1997 and 1998.

I müng feediig flymg spiral basking perching I1 , Ba haviour Figure 8. Total behaviour budget of the ringlet, Coenonympha tullio, at the RJ Hilton Centre (EU) site and Stone RoaWictoria Road (SV) site in the University of Guelph arboretum, summer 1997 and SV site, summer 1998.

SV site '97 : i SV siîe '98 ! ;

mting feeding flying spiral basking perching Be haviour Figure 9. Variation in behaviour budget of the European skipper, Thymeficus lineofa, in the preseace or absence of the tawnysdged skipper, Polites themi~ocfes,and ringlet, Coenonympha tuffia at the Stone RoadlVictoria Rond (SV) site in the University of Guelph arboretum, summer 1998.

SV site 1998 ab~#nce/pregenceof tawny*dged skipper

feeding fiying s puai basking perchkg ûo haviour

SV site 1998 absencelpreipente of ringlet

mting feeding flying spiral basking perchbg 8.haviour Figure 10. Variation in behaviour budget of the tawny-edged skipper, Polites thernistocies, in the presence or absence of the European skipper, Thymeiicus lineola at the Stone Road/Victoria Rond site in the University of Guelph arboretum, summer 1998.

1 [aabsence 1 !

feediig spiral ûohaviour Figure 1 1. Variation in bebaviour budget of the ringlet, Coenonympha tuffia, in the presence or absence of the European skipper, Thymeficus fineoia, and tawny-edged skipper, Poiites themistocles, at the Stone RoadlVictoria Road (SV) site in the University of Guelph arboretum, summer 1998.

I SV site 1998 absencelpresence of European skipper

f eediig spiral Bohaviour

SV site 1998 abrpencelpresence of tawnysdged #kipper Figure 12. Within site variation in behaviour budget of the European skipper, Thymelicus lineola, in the presence or absence of a conspecific at the Stone RoaWictoria Road site in the University of Guelph arboretum, summer 1998.

i presence 1 1'

mting feeding fiying spiral basking perching bohaviour Figure 13. Within site variation in bebaviour budget of the the tawny-edged skipper, Polltos themistocles, in the presence or absence of a conspeclc at the Stone RoadNictoria Road site in the University of Guelph arboretum, summer 1998.

nialhg feeding flying spiral perching basking be haviour Figure 14. Within site variation in bebaviour budget of the ringlet, Coenonympha tulliP, in the presence or absence of a conspecific ai the RI Hilton Centre site in the University of Guelph arboretum, summer 1997.

1 joabsensei! i i presence 1 I

1

mting feeding flying spiral perching basking bahaviour