Relationships Between Environmental Characteristics and Macroinvertebrate Communities in Seasonal Woodland Ponds of Minnesota

J. N. Am. Benthol. Sw., 2004, 23(1):50-68 Q 2004 by The North American %ntholagical Society Relationships between environmental characteristics and macroinvertebrate communities in seasonal woodland ponds of Minnesota

Department of EntomEog, Urziwsity of Georgia, Athens, Georgia 30602 USA

USDA Forest Service, North Central Research Station, 2831 East Highq 269, Grand Rqids, Minnesota 55744 USA

Abstract. We related macroinvertebrate communities and environmental variables in 66 small seasonal woodland ponds of northern Minnesota, USA. These wetlands were relatively pristine, being embedded in 50- to 100-y-old Pd-growth forests. Macroinvertebrate taxon richness in ponds increased as hydroperiods lengthened, tree canopies opened, water pH declined, and litter input decreased. Eighteen macroinvertebrate taxa were widespread (occurred in >5O0/0 of ponds), and hydrology water chemistry, geomorphology vegetation, occurrence of other macroinvertebrate taxa, and presence of amphibian larvae each explained some variation in relative abundance of widespread macroinvertebrates. The first 4 axes of a canonical correspondence analysis explained 37% of total variation in relative abundance of widespread macroinvertebrate taxa. Overall, however, macroinvertebrates were remarkably unresponsive to environmental variables. Most relationships between macroinvertebrates and environmental variables were nonsignificant, and the few significant relationships observed were weak (<20% of variation). We suggest that this lack of response occurs because most macroinvertebrates in seasonal woodland ponds are habitat generalists. These species routinely endure pronounced and unpredictable environmental changes; hence, they possess a durability that makes them resistant to most natural variation in habitat conditions. Key words: wetlands, invertebrates, hydroperiod, canopy cover.

There are several hypotheses about ecological indirect, with hydrology affecting distributions controls on macroinvertebrate communities in of predaceous salamanders, which in turn af- seasonal ponds. The treatise by Wiggins et al. fected invertebrate abundance. Few would argue (1980) on seasonal ponds in Ontario focused at- that wetland organisms must deal effectively tention on hydroperiod, and maintained that with temporary drying, but Williams (1996) drying prevented many organisms from exploit- suggested that drying is not a difficult barrier ing these temporary habitats. Recent studies by to overcome because the ability to survive dry Schneider and Frost (1996) in 7 Wisconsin periods has evolved repeatedly in a wide range ponds, Brooks (2000) in 5 Massachusetts ponds, of unrelated wetland taxa. For species adapted and Fairchild et al. (2003) in 9 Pennsylvania to seasonal wetlands, drying may not be a ma- ponds contrasted invertebrate communities jor environmental constraint. along a hydroperiod gradient, and reported that Wetland ecologists have tacitly assumed that faunas from ephemeral habitats were different water chemistry is an important influence on from those in permanent ponds. However, in a wetland invertebrates (Batzer and Wissinger more extensive study of 41 ponds in Colorado, 1996), although little quantitative evidence ex- Wissinger et al. (1999) found little evidence that ists to support this hypothesis. In semi-arid hydrology directly affected community struc- western Australia, Growns et al. (1992) found ture beyond the fact that only a few inverte- that invertebrate communities varied with water brates exploited extremely short-duration color and nutrient concentration. Nutrient levels ponds. Wissinger et al. (1999) suggested that the also limited invertebrates in an oligotrophic most important influence of hydroperiod was marsh in Canada (Campeau et al. 1994, Gabor et al. 1994). In some North American prairie E-mail addresses: [email protected] wetlands, highly saline or alkaline conditions * bpalik632fs.fed.u~ permit only the most tolerant organisms to per- ,ASONAL WOODLAND PONDS sist (Euliss et al. 1999, Lovvorn et al. 1999). However, each of these wetlands showed extreme (high or low) chemical concentrations, which in some cases were anthropogenically in- duced. Examples of associations between water Rice River quality and invertebrates from natural habitats Lake plain with more moderate chemistries appear to be End moraine lacking (Batzer and Wissinger 1996, Wissinger Study pond et al. 1999, Battle and Golladay 2001). The hydrology and water chemistry of seasonal ponds both are undoubtedly governed by landscape features, so one might expect rnac- roinvertebrate communities to vary with changes in landscape characteristics, such as landform or soil type. However, limited information exists on how macroinvertebrates in seasonal ponds are influenced by landscape features (Euliss et al. 1999, Hall et al. 1999). Some authors have speculated that patch size influences biotic diversity of seasonal ponds (Ebert and Balko 1987, Hall et al. 1999, Wissinger et al. 1999), so rnac- roinvertebrate communities may vary with Sucker Lakes watershed I pond size. In addition to abiotic factors, biotic features Outwash plain also may influence invertebrates in seasonal End moraine woodland ponds. Recent evidence suggests Study pond that, like streams (Wallace et al. 1997), the con- FIG. 1. Locations of the Sucker Lakes (lat 47'15'N, dition of the surrounding upland forest and lit- long 94'30'W) and Rice River (lat 417045'N, long ter input influence macroinvertebrate commu- 93'37'W) watersheds in northern Minnesota's Chip- nities in ponds (Higgins and Merritt 1999, Batz- pewa National Forest. er et al. 2000, Palik et al. 2001). Entrekin et al. (2001) and Battle and Golladay (2001) hypoth- esized that differences in plant communities to test competing hypotheses are even rarer (but among ponds affect distributions of wetland in- see Wissinger et al. 1999). The goal of our study vertebrates by altering food quantity and qual- is to describe macroinvertebrate communities ity. In addition to bottom-up trophic influences and habitat conditions in a large set of seasonal with plants, macroinvertebrates in seasonal woodland ponds in Minnesota, USA, and to de- ponds also may be controlled by predation termine how much variation in composition is (Wellborn et al. 1996, Wilbur 1997, Wissinger et explained by various abiotic and biotic habitat al. 1999). Most research in seasonal ponds has factors. We also provide a correlative means of focused on invertebrate predation by vertebrates testing and comparing some of the emerging (see reviews by Batzer and Wissinger 1996, Wis- hypotheses regarding the maintenance of rnac- singer 1999), whereas the importance of preda- roinvertebrate communities within seasonal ceous macroinvertebrates has not been evaluat- ponds. ed (but see Higgins and Merritt 1999, Battle and Golladay 2001). Methods With the possible exception of hydrology, there is little compelling evidence to support Study zwterskds and pond selection any hypotheses regarding controls on macroinvertebrates in seasonal ponds. Very few stud- Wi, conducted our study on the Chippewa ies have addressed any particular hypothesis, National Forest in north-central Minnesota and most published studies have been conduct- within the Sucker Lakes and Rice River water- ed on a small number of sites (40). Attempts sheds (Fig. 1). Dominant glacial landforms in- D. P. BATZERET AL. cluded ground moraine and outwash plain in tern, with inline persulfate digestion for total N the Sucker Lakes watershed and end moraine and total I? Total organic C was measured using and lake plain in the Rice River watershed. Up- a Dorhmann DC-190 analyzer. We measured land forests within study watersheds were color (as absorbance) of water samples using a mostly mixed pines (Pinus banksiana, I! resinosa, Spectronic 21D. and/or I? strobus) on the outwash, and mixed Pod size.-We determined pond surface area hardwoods (P'opulus trmuhides, I? ~andidentata, using the seasonal high-water level in 1998. Acer saccharum, Tilia amevimna, and/or Qwcus Presence of high-water marks, such as sedi- rubra) on the moraines and lake plain. Glacial ment-coated or recently saturated leaf litter, was landforms were mapped as part of the National used to establish pond margins. We measured Forest's ecological classification and inventory margin-to-margin pond length in 2 perpendic- (Chippewa National Forest 1996). In addition, ular dimensions, and used those dimensions to National Fbrest personnel identified and digi- estimate surface area using the formula for an tized all seasonal ponds in study watersheds us- ellipse. ing 1:24,000 leaf-off color-infrared air photog- Vegetation.-In 1998 in each pond, we estab- raphy. lished 1 line transect that spanned the basin's We randomly selected 66 ponds for study in longitudinal axis, and recorded herbaceous 4 glacial landforms (Fig. 1). We constrained our plant cover and coarse woody debris (CWD) selection of ponds using the following criteria: along the transect using the line-intercept meth- 1) the surrounding forest was >50 y old; 2) od, We defined CWD as trunks and branches ponds and surrounding forests showed no evi- >5 cm diameter at their narrowest point within dence of recent disturbance; 3) pond area was the pond basin. We assigned plant cover, as a >0.02 but <0.5 ha; 4) ponds had mineral or distance along the transect, to categories includ- mixed mineral and organic soil substrates, as ing sedge, grass, floating-leaved plants, sub- opposed to peat; and 5) water depth in pond mersed plants, or bryophytes. basins at the time of selection in spring 1997 was In each pond, we sampled woody vegetation >15 cm. In total, we selected 25 ponds in the in 5.6-m radius circular plots centered on 3 ground moraine, 12 ponds in the outwash plain, equidistant points on the transect line; in some 25 ponds in the end moraine, and 4 ponds in small ponds we could only establish 1 or 2 the lake plain. points. In each plot, we recorded the species and diameter at 1.4 m height of each tree 210 Sampling cm. In mid-summer we estimated pond overstory canopy cover above the shrub layer using a Hydrology-We measured water depths in spherical densiometer. Ponds were small so den- each pond using a metal staff gage placed in siometer readings reflected canopy cover over the deepest part of each basin. We read gages the basin and the upland forest adjacent to weekly to biweekly between 1 April and 30 Sep- ponds. In 1998, we placed 1 or 2 litter traps in tember 1998 and 1999, sampling all 66 ponds each basin, depending on pond size, to estimate within 1 or 2 d. Ponds in the Sucker Lakes wa- input of coarse particulate organic matter tershed also were monitored in 1997. (CPOM). We collected litter monthly from May Water chemistry.-We collected water samples through early September and then biweekly un- from each pond, if they held water, on the same til early November, with a final collection in ear- dates we read staff gages. We stored unfiltered ly spring 1999. We dried litter at 65OC for 48 h water at 4OC in 0.5-L polyethylene bottles for a and then weighed it (nearest 0.1 g) to determine maximum of 30 d before analysis. We measured dry mass. pH (Corning model 440 meter and Orion 8102 Macroinvevtebrates.-We sampled macroinver- electrode), conductivity (YSI Model-35), and al- tebrate assemblages in each of the 66 ponds kalinity (autotitration to pH 4.5, Mettler DL20 while they held water in 1998 and 1999. We titrator followed by Gran plot analysis). We de- sampled in mid May to collect the spring fauna termined IW3-N (detectable to 0.02 mg/L), and again in late June to collect later colonizers. NH,-N (0.02 mg/L), total N (0.02 mg/L), and We used a D-frame net (30 cm width, 1 mm total P (0.5 mg/L) by colorimetric procedures mesh) because it samples macroinvertebrate on a Lachet Quik Chem 8000 flow-injection sys- communities from wetlands efficiently and pre- 20041 MACROI~R~BWESIN SEASONAL brWDLAND PONDS 53 cisely (Cheal et al. 1993, Batzer et al. 2001). The from each pond over the 2-y study. We used net mesh was small enough to retain most in- families rather than genera for richness analyses vertebrates but large enough to prevent exces- because we lacked the expertise or budget to sive clogging by fine sediments (Batzer et al. quantify and classify all invertebrates to genus 2001). During each sampling visit, we used (e,g., Ceratopogonidae, early instar Chironomi- three l-m long sweeps, the lbtnear the pond dae, Ostracoda). For relative abundance, we re- edge, the 2ndin the pond center, and the 3rd ei- stricted our analysis to those families collected ther at a halfway point between the edge and in >50% of the ponds (= widespread taxa); in- center or in a subhabitat (e.g., in emergent plant clusion of less-widespread taxa with a large stands, woody debris) that otherwise was not number of 0 abundance values would have com- sampled in the first 2 sweeps. Wetted areas var- promised analyses. We generated composite ied among ponds and changed temporally, al- macroinvertebrate values for each pond by av- though we did not weight our sampling effort eraging all measurements collected over the 2-y by area. We scraped the net horizontally along study. However, for some taxa that emerged or the pond bottom to collect both benthic and diapaused prior to June sampling (i.e., Culicidae, free-swimming organisms. Contents of the 3 Limnephilidae, Daphniidae), we used only May sweeps were pooled into 1 composite sample collections to calculate relative abundance. We per pond, and the collected material was pre- could not extrapolate relative abundances to served with 95% ethanol. In the laboratory, we pond abundance because the wetted area of separated macroinvertebrates from mud and ponds changed throughout the study. Therefore, detritus by hand and identified them to family our measures of basin size did not always re- or genus using Pennak (1989), Thorp and Cov- flect availability of aquatic habitat. ich (1991), and Merritt and Cummins (1996). We Unimriate analyses.-We restricted our analy- expressed relative abundance of macroinverte- ses of hydroperiod to the 183-d span from 1 brates per pond sample, encompassing -0.9 m2 April through 30 September, a time when ponds of wetted habitat. were ice free. We estimated hydroperiods by de- Amphibians.-We used dipnets and funnel termining cumulative time (d) each pond was traps to sample amphibian (frog and salaman- flooded. If a pond dried or reflooded, we as- der) larvae. We conducted dip netting from late sumed that the hydrologic transition occurred May to early June in 1998 and 1999, a time when at the midpoint between monitoring dates. For larvae were identifiable to species. Fbr each our lsthydrologic analysis, we related mean hy- pond, we used a time-constrained search in droperiods with macroinvertebrates that exploit which 2 people swept the water for 15 min. We ponds. We calculated hydroperiod means using held captured amphibians in buckets until the only 1998 and 1999 data (1 April-30 September) end of the sampling period, and then identified because in 1997 hydroperiods were measured and released them. We used hardware-cloth (6 only in the Sucker Lakes watershed. Two-year mm mesh) funnel traps to sample larvae from mean hydroperiods and macroinvertebrate 3 June to 9 July. We used either 2, 4, or 6 un- measures for each pond were related using sim- baited traps per pond, depending on pond size. ple regression. For our 2ndhydrologic analysis, We spaced traps evenly across ponds, perpen- we divided the 66 ponds into 3 equal groups (n dicular to shore, in water deep enough to sub- = 22), with thel" group having the shortest hy- merge most of the trap yet provide an air space droperiods (dry >49 d per summer), the 2nd for adult amphibian respiration. We checked group having intermediate hydroperiods (dry traps daily for 3 d. We identified trapped arn- 29-48 d per summer), and the 3rdgroup having phibians to species and released them. the longest hydroperiods (dry <28 d per summer). We then contrasted the presence and ab- Statistical analyses sence of individual taxa among the 3 hydroperiod groups using x2 tests. Hydroperiod changes Macroinwtebrate measures.-We used richness from year to year, so we conducted a 3rd hydro- and relative abundance of the most common logic analysis to assess impacts of hydroperiod taxa to assess macroinvertebrate relationships for a specific year. We regressed taxon richness with habitat variation. Fbr richness, we deter- and relative abundances of widespread taxa in mined the total number of families collected 1998 or 1999 with the hydroperiod of the pre- D. P. BA~RET AL. [Volume 23 vious year, reasoning that conditions for repro- vironmental variables. We performed 2 tests, duction and aestivation by macroinvertebrates one based on the 1st canonical eigenvalue and the previous year might influence populations one based on the sum of all canonical eigenval- the subsequent year. We excluded ponds in the ues. The resulting tests determined the signifi- Rice River watershed for the 1998 analysis be- cance of the 1st ordination axis and that of all cause 1997 hydroperiod data were not available. canonical axes together, respectively. krexample, We restricted our analyses of water chemistry to evaluate the significance of the 1st CCA axis, a to 1998 data because collections were less com- p-value is computed as p = (1 + n)/(l + N), plete for 1997 and 1999, and chemical conditions where n = the number of randomizations (per- in 1998 reflected those in the other years (DPB, mutations) with an eigenvalue greater than or unpublished data). We related 1998 mean water equal to the corresponding observed eigenvalue chemistry measures to macroinvertebrate vari- and N = the total number of randomizations ables (2-y composite measures) using simple re- (permutations). gression. Wi3 also used l-way ANOVA and a Tu- a-wlues and transformtions.-We used a criti- key test to contrast macroinvertebrate measures cal value of a = 0.05 for univariate tests involv- among the 4 glacial landform types, and a t-test ing taxon richness and the CCA ordination. Bon- to compare macroinvertebrate measures be- ferroni adjustments of a values for testing mul- tween the 2 watersheds. Macroinvertebrate re- tiple variables were unnecessary for univariate sponse measures were related to pond size, can- tests because we did not hypothesize that rich- opy cover, sedge cover, CWD cover, tree basal ness would respond to every measure (see Per- area, and litter input using simple regression. A neger 1998). However, for univariate analyses correlation matrix contrasting patterns of rela- relating relative abundance of individual taxa tive abundance among all widespread macro- and environmental variables, we used a more con- invertebrate taxa was used to assess interrela- servative a value of 0.01. We used log(x + 1) tionships among taxa. Relative abundance of transformations for numerical data and arc sin amphibians was extremely variable from year to transformations for % data to meet assumptions year, and quantitative results from dipnetting of regression and ANOVA. Data were not trans- and funnel traps did not always agree. There- formed for CCA. fore, we pooled dipnet and funnel trap data to determine pond-specific presence or absence of Results amphibians, and we contrasted macroinvertebrate measures between ponds with or without Faunal composition an amphibian species using a t-test. Multimriate analysis.-Abundances of wide- Forty-five taxa (families or orders) of aquatic spread taxa were related to all habitat variables macroinvertebrates were collected from the 66 with canonical correspondence analysis (CCA), study ponds (Appendix). Numbers of taxa col- using CANOCO (C. J. F. ter Braak and A. Smi- lected over the 2-y period ranged from 8 to 30 lauer. 1998. CANOCO reference manual and per pond, with some taxa including multiple user's guide to CANOCO for Windows: soft- genera (Appendix). Seventeen families were ware for canonical community ordination, ver- widespread (occurring in >50% of the habitats; sion 4.0, Microcomputer Power, Ithaca, New Table 1). The tanypodine Chironomidae were York). CCA is a direct gradient analysis that considered as the widespread taxon (78% uses multiple regression to develop ordinations occurrence) because their mostly predatory be- that represent taxa distributions constrained by havior makes them ecologically unique from the environmental factors such as landform, hydro- rest of Chironomidae.. period, canopy cover, etc. We coded categorical Primary consumers numerically dominated variables as a set of dummy variables, one for the 18 widespread taxa, including shredders each category of the variable (i.e., 2 watersheds, (Limnephilidae, Haliplidae), scrapers (Physidae, 4 landform types). We scored values for individ- Planorbidae, Lymnaeidae), collector-gatherers ual ponds as either 0 or 1, depending on its oc- (non-Tanypodinae Chironomidae, Lumbriculi- currence in the category. We used a Monte Carlo dae, Daphniidae, Culicidae, Cyprididae, Dixi- permutation test to determine the statistical sig- dae), and collector-filterers (Sphaeriidae). Pred- nificance of the relation between species and en- atory beetle larvae and adults (Dytiscidae, Hy- 20041 MACROIWERTEBRA~SIN SEASONAL 1,VOODLAND PONDS 55

TABLE1. Percent occurrences of the 18 most wide- not 1998, hydroperiod of the previous year was spread macroinvertebrate taxa (families or subfami- positively related to taxon (r2 = 0.11, lies) in 66 seasonal woodland ponds in northern Min- =: 0.009). nesota. Hydroperiod influenced relative abundances of 4 of the 18 widespread taxa. Mean hydroper- Group '10 occurrence iod was positively related to relative abundanc- Chironomidae (non-Tmypodinae) es of limnephilids (r2 = 0.17; p = 0.001), sphae- Lumbriculidae riids (r2 = 0.14, p = 0.002), haliplids (rh0.11, Sphaeriidae p = 0.006), and libellulids (r2= 0.11, p = 0.008). Dy tiscidae Hydroperiod in 1997 was positively related Physidae Chaoboridae to relative abundance of limnephilids in 1998 Daphniidae (r2 = 0.34, p = 0.001), but hydroperiod in 1998 Culicidae Lknnephilidae Planorbidae Tanypodinae Haliplidae Libellulidae HydrophiLlidae Cyprididae Ceratopogonidae Dixidae Ly maeidae

drophilidae), dipterans (Chaoboridae, Tanypo- dinae, Ceratopogonidae), and dragonfly naiads (Libellulidae) also were widespread and occa- sionally abundant. Larval wood frogs (Rana syl- vatica) and blue-spotted salamanders (Ambysto- ma lateuale) occurred in 54 and 40 of the 66 ponds, respectively.

Xelationships between macroinvertebrates and habitat charactevis tics Univariate analyses.-Hydroperiods varied greatly from year to year, with 1998 being the driest summer, 1999 the wettest, and 1997 being intermediate (Fig. 2A). Some ponds were peren- nially flooded, whereas others were dry for more than half of the sampling period (Fig. 2B). Most ponds that dried reflooded in autumn 1997 and 1999, but 45 of 66 (68%) ponds re- % of time flooded mained dry in autumn 1998. The total number of macroinvertebrate taxa was positively related FIG. 2. Mean (t1 SE) annual variation in pond hydroperiod from the 1 April to 30 Sptember (183 d) to mean hydroperiod (r2 = 0.41, p < 0.001, ice-free period in which ponds held water, during Fig. 3A), largely because glossiphoniids (x2test, 1997 (tz = 37), 1998 (n = 66), and 1999 (n = 66) (A). p = 0.004), erpobdellids @ < 0.001), libellulids Statistics for 1997 include only the data from the Suck- @ = 0.002), limephilids @ < 0.0001), haliplids er Lakes watershed. Percentage of the 1 April to 30 (p = 0.002), tanypodines (p < 0.001), and most September period in which individual ponds (n = 66) rare taxa (e.g., leptocerids, pleids) occurred al- held water during 1998 and 1999 (yearly mean for most exclusively in wetter habitats. In 1999, but each pond) (B). D. P. BATZER ET AL. [Volume 23

(0 u, 50 100 150 200 a> L= Average number of days flooded I: 0 .L.- c 0 i5 t- 30~B a

FIG. 3. Associations of macroinvertebrate taxon richness in 66 seasonal woodland ponds with hydroperiod (mean number of days each pond held water from 1 April to 30 September) (A), water pH (B), pond size (C), canopy cover (Dl, and litter input (E). Taxon richness was defined as the number of aquatic macroinvertebrate families collected over the 2-y study period (1998-1999). Statistically sigruficant relationships (p < 0.05) are indicated by regression lines. was negatively related to limephilid abun- (Table 2). Many of the chemistry variables were dance in 1999 (r2 = 0.31, p < 0.001). Hydroper- interrelated, with strong positive relationships iod in 1998 was positively related to abundance among pH, alkalinity, and conductivity; be- of haliplids in 1999 (r2 = 0.14, p = 0.002). tween total organic C and water color; and Most water chemistry variables differed among total N, NO,-N, and NI--I,-N @ < 0.05). among ponds by 1 or 2 orders of magnitude However, variation in macroinvertebrate rich- ]MACROINVERTEBRA~'ESIN SEASONAL WOODLAND PONDS

- - a> C r: Pond surface area (m2) 0 .L-

e m- e... r) 00a.

0 25 50 75 100 5% canopy FIG. 3. Continued. ness or relative abundance was related infre- related with pH (u2 = 0.14, p = 0.002), NH,-N quently to chemical attributes. Macroinverte- (r2 = 0.14, p = 0.002), alkalinity (r2 = 0.13, brate taxon richness was related to only one p = 0.003), conductivity (r2 = 0.12, p = 0.004), chemical variable, pH, and that relationship was and total N (r2 = 0.1 1, p = 0.007). Both lyrnnaeid weak (r2 = 0.06, p = 0.051, Fig. 3B). Limnephilid and ostracod abundances were positively relat- relative abundance was positively related with ed to NH4-N (r2 = 0.23, p < 0.001; r2 = 0.22, alkalinity (r2 = 0.35, p < 0.001), conductivity p < 0.001, respectively) and total N (r2 = 0.25, (r2 = 0.30, p < 0.001), and pH (r2 = 0.17, p < 0.001; r2 = 0.15, p = 0.002, respectively). p = 0.001). Planorbid abundance was positively Macroinvertebrate taxon richness did not differ [Volume 23

Litter input (Mglha) FIG. 3. Continued. between the 2 watersheds, but did differ among ever, some taxa were probably missed in large landforms (ANOVA, R2 = 0.18, p < 0.006), with ponds, basin size did not always reflect wetted higher richness in the outwash plain and end area, and large habitats would support the most moraine than the ground moraine @ < 0.05). total invertebrates if abundances per sample Non-Tanypodinae midges @ = 0.009), dytis- were similar. Therefore, the lack of significant cids (p = 0.001), and chaoborids (p = 0.006) relationships between macroinvertebrate mea- each had higher relative abundance in Sucker sures and basin size should be interpreted with Lakes ponds than in Rice River ponds. Dytiscid caution. abundance varied significantly with landform Canopy cover averaged 79.5% (SE = 2.6), (R2 = 0.33, p < 0.001), with more beetles occur- with a median cover of 88%. Eight of 66 ponds ring in ponds in the outwash plain than in the were mostly open (<50% cover). Overstory tree ground and end moraines (p < 0.05). Pond basin basal area averaged 10.3 m2/ha (SE = 1.3). The size averaged 715.5 m2 (SE = 56.4), ranging input of litter from trees averaged 2.03 Mg dry from 79 to 2141 m2. Neither taxon richness mass ha-l y-I, consisting of material from pond (p = 0.169, Fig. 3C) nor relative abundance of any trees and shrubs and surrounding upland trees. of the 18 widespread macroinvertebrate taxa was Canopy cover, tree basal area, and litter input related to pond basin size (all p > 0.01). How- all were positively related (p < 0.05). Cover of CWD in ponds averaged 8.7% (SE = 0.8). Sedge TABLE2. Water chemistry variables of 66 seasonal (Carex spp.) was the most common herbaceous woodland ponds in northern Minnesota. plant in ponds, averaging 56.3% cover (SE = 3.5, range 0-100%). Macroinvertebrate taxon rich- Variable Mean (SE) Range ness increased with decreasing canopy cover (r2 = 0.16, p = 0.001, Fig. 3D) and decreased with increasing litter input (r2 = 0.08, p = 0.021, Fig. Conductivity ( pS /cm) 3E). Numbers of dytiscids (r2 = 0.12, p = 0.005), Color (absorbance units) haliplids (r2= 0.12, p = 0.004), and hydrophilids Total C (mg/L) (r2 = 0.14, p = 0.002) were negatively related to NH4-N (mg/L) canopy cover. Haliplid (rZ= 0.13, p = 0.003) and NO3-N (mgf L) dytiscid (r2 = 0.10, p = 0.012) relative abun- Total N (mg/L) dances were also negatively related to litter in- Total P (mg/L) put. Hydrophilid relative abundance decreased 20041 MACROINVERTEBRA~SIN SEASONAL WOODLAND PONDS 59

TABLE3. Summary of canonical correspondence analysis (CCA) results, relating relative abundances of 18 widespread macroh~~ertebratetaxa to mviromental variables in 66 seasonal woodland ponds in northern Minnesota. Overall CCA was significant at p = 0.01; CCA axis 1, p = 0.155 (Monte Carlo test).

CCA axis

Eigenvalue 0.297 0.173 0.112 0.101 Taxa-environtnent correlation 0.727 0.821 0.731 0.737 Cumulative % variance of taxa 16.1 25.5 31.6 37.1 Cumulative % variance of taxa- environment relationship 33.8 53.4 66.1 77.6

(r2 = 0.12, p = 0.004), whereas limnephilid lymnaeids and daphniids. Some associations abundance increased (r2 = 0.10, p = 0.012) with identified by CCA were not detected in univar- increasing CWD. iate analyses. Fbr example, culicids were the Mltimuiafe ana2ysis.-'The first 4 axes of the macroinvertebrates most strongly associated CCA explained 37.1% of total variation @ = 0.01, with CCA axis 1, which accounted for most of Table 3) in relative abundances of the 18 wide- the total variation. However, none of the uni- spread taxa; the first 2 CC4 axes alone account- variate analyses between culicids and habitat ed for 25.5% of total variation (Fig. 4, Table 3). characteristics were significant, probably be- Axis 1 (16.1% of variation) was largely defined cause culicids were abundant in only 3 of 66 by tree basal area, pond hydroperiod, and oc- ponds. In addition to showing extremely high currence of ponds in the glacial lake plain. Culi- culicid abundances, those 3 ponds had low tree cids and hydrophilids were associated with axis basal area and short hydroperiod. However, nei- 1, being more abundant in ponds with low tree ther basal area nor hydroperiod explained sig- basal area and shorter hydroperiods; culicids nificant variation in culicid abundance across all were also less abundant in glacial lake plain 66 ponds in the univariate analyses. ponds (Fig. 4). The Monte Carlo p-value of 0.155 for axis 1 indicates that, although this relationship explained the most variation, it was not Relationships among mmroinvevtebrate taxa and strong. Axis 2 (9.4% of total variation) was de- between macroinvertebr&es and amphibians fined by NH,-N, total N, alkalinity, water color, and the occurrence of ponds in the outwash Relative abundances of dytiscids (r2 = 0.23, plain. In particular, ostracods, lymnaeids, plan- p < 0.001), chaoborids (r2= 0.23, p < 0.001), and orbids, and to a lesser degree dytiscids, were lumbriculids (r2 = 0.10, p = 0.012) were posi- more abundant in ponds with higher concentra- tively related to relative abundances of non-Tan- tions of NH,-N and total N, higher alkalinity, and lower color, and in outwash plain ponds. In ypodinae midges, and dytiscid and chaoborid contrast, dixids and physids were somewhat relative abundances were positively related more abundant in ponds with lower NH4-N, to- (r2 = 0.24, p < 0.001). Planorbid, lymnaeid, and tal N, alkalinity; and higher color, and in ponds ostracod relative abundances were positively outside of the outwash plain. Axes 3 and 4 (6.1% correlated (all p < 0.001). Ponds with larval and 5.5% of total variation, respectively, not wood frogs (ANOVA, R2 = 0.14, p = 0.002) or shown in Fig. 41 were defined bv conductivitv blue-spotted salamanders (R2 = 0.08, p = 0.019) U 1 J J and alkalinity (axis 3) and watershed (axis 4). each supported a greater number of macroin- Ponds having higher conductivity and alkalinity vertebrate taxa than ponds without these am- showed higher relative abundances of limne- phibians. Relative abundance of chaoborids was philids, physids, planorbids, and tanypodines. greater in ponds with frog larvae (R2 = 0.13, Sucker Lakes ponds showed higher abundances p = 0.003) or salamanders (R2= 0.12, p = 0.005). of non-Tanypodinae midges, chaoborids, dytis- Ponds with frog larvae @ = 0.024) or salaman- cids, lumbriculids, and hydrophilids whereas ders (p = 0.006) were wetter than ponds without Rice River ponds had higher abundances of amphibians. D. P. BATZERET AL. [volume 23

FIG. 4. Canonical correspondence analysis (CCA) ordination depicting relationships among relative abundances of widespread macroinvertebrates and environmental variables. The importance of an environmental variable in determining relative abundance of taxa in different ponds is reflected in the length and orientation of the arrows associated with each variable relative to the location of taxa and ponds on the triplot. For example, NH,-N concentration is positively associated with ponds in the upper half of the triplot. These ponds had higher abundances of Cyprididae, Lymnaeidae, and Planorbidae. For clarity, only taxa and environmental variables having high discriminating power for distinguishing among ponds are shown.

Discussion equivocal results. The value of species or genus vs family classification recently has been debat- Numerous significant univariate and multi- ed for streams (Bailey et al. 2001, Lenat and variate relationships between macroinverte- Resh 2001) and, in wetlands, taxonomic resolu- brates and environmental variables were detected (Table 4), but the more striking feature of our tion at the family level or higher may mask sig- study was that most relationships were nonsignificant relationships (King and Richardson nificant. Furthermore, most of the significant re- 2002). Relationships at the genus or species level lationships were weak, explaining only 4 to 20% might not have been detected by using the fam- of variation. Taken together, the general lack of ily or subfamily level in our analysis for diverse significant and strong relationships among mac- groups (i.e., Tanypodinae and non-Tanypodinae roinvertebrates and habitat variables may be the midges, Dytiscidae, Hydrophilidae). However, most important finding of our study. 11 of 18 widespread taxa in our study consisted Several factors may have contributed to our almost exclusively of one genus (i.e., Sphaeri- TABLE4. Statistically sipficant regressions (denoted by X) between environmental variables or composite canonical correspondence analyses (CCA) environmental axes and relative abundances of widespread macroinvertebrate taxa (ordered by highest to lowest % occurrence) and macroinvertebrate taxon richness from 66 seasonal woodland ponds in northern Minnesota. For simplicity, some univariate variables were grouped into more general categories, but macroinvertebrates may have only responded to a subset of variables in the category (i.e., geology-watershed, landform, pond size; ions-pH, conductivity, alkalinity; nutrients-NO,-N, NH4-N, total N, total P; dissolved C-total organic C, color; detritus-litter input, coarse woody debris; plant cover-sedge cover, tree basal area; vertebrates-frogs, salamanders). The most influential variables for each CCA axis were as follows: CC axis l-composite of tree basal area, hydroperiod, and ponds outside of the lake plain; CCA axis 2-composite of NH4-N, total N, alkalinity, and water color; CCA axis 3-composite of conductivity and alkalinity; and CCA axis 4-watershed. Taxon richness was not included in the CCA.

Dis- CCA axis Invertebrate Hydro- Geol- Nutri- solved Can- Detri- Plant Verte- taxon period ogy Ions ents C opy tus cover brates 1 2 3 4 Non-Tanypodinae X Chironornidae Lumbriculidae Sphaeriidae Dytiscidae X Physidae Chaoboridae X Daphniidae Culicidae Limnephilidae Planorbidae Tanypodinae Haliplidae Libellulidae Hydrophilidae Cyprididae Ceratopogonidae Dixidae Lymnaeidae Taxon richness X X [Volume 23 idae, Physidae, Planorbidae, Lymnaeidae, Daph- was less fraught with such assumptions than niidae, Libellulidae, Limephilidae, Haliplidae, univariate analyses but, like univariate tests, Culicidae, Chaoboridae, Dixidae; Appendix), yet CG1. accounted for only a few taxa and a minor these taxa were no more responsive to environ- amount of the total macroinvertebrate variation mental variation than the taxonomically diverse (37%). In summary, we acknowledge that the taxa (Table 4). above factors influenced our results, but argue Our selection of ponds was restricted to those below that weak relationships between pond occurring in mature 2nd-growth forest thereby macroinvertebrates and their physical environ- eliminating many sources of environmental var- ment should be expected. iation. If ponds were environmentally homoge- neous, then so too might macroinvertebrate Weak influence of environmental variation on communities. However, environments and mac- mmroinvevtebrates roinvertebrates were heterogeneous among ponds. krexample, pond hydroperiods ranged Variation in hydroperiod was one of the stron- from ephemeral to almost permanent (Fig. 2B), ger influences on macroinvertebrates in the sea- water chemistry variables routinely varied by 1 sonal woodland ponds (Table 4), but with some or 2 orders of magnitude (Table 2), and tree can- caveats. A relatively strong relationship between opy and sedge cover ranged from negligible to taxon richness and hydroperiod was detected; 100%. Macroinvertebrate relative abundance however, this association occurred primarily be- was equally variable among ponds, with stan- cause rare taxa persisted only in the wettest dard deviations for taxa frequently exceeding ponds. In contrast, hydroperiod had relatively means. little influence on widespread taxa, in that the It is also possible that sampling methods same macroinvertebrate taxa were numerically could have influenced results. Sweep nets collect dominant whether ponds held water continu- large samples, but many taxa were probably ously or were dry for several months. Thus, it missed with this method, especially in large appears most organisms became abundant in ponds. Samplers that use mesh also have inher- ponds irrespective of hydroperiod, probably be- ent biases. Small organisms may have passed cause the degree of variation in hydroperiod through the mesh while others may have been was insufficient to produce marked changes in pushed out of the front of the sampler when widespread macroinvertebrate populations. Hy- mesh clogged (Batzer et al. 2001). Moreover, our droperiod naturally varies unpredictably in 4-date sampling schedule may have missed cer- many seasonal ponds, so macroinvertebrates tain taxa that developed before, between, or af- that successfully exploit these habitats probably ter our sampling. These sources of error could can tolerate a broad range of hydroperiod have influenced results of individual analyses, lengths. Hydroperiod probably restricts distri- but it seems unlikely that the general pattern of butions of organisms that use seasonal wood- few or weak relationships between macroinver- land ponds as marginal habitats (i.e., rare taxa), tebrates and habitat variables could have been but it may be relatively unimportant to success- eliminated simply by sampling refinements. ful taxa. Statistical issues also could have influenced Our opinion on the importance of hydroper- interpretation of results. Our sample size of 66 iod appears to contradict that of other studies should have been sufficiently large to detect in seasonal wetlands. Schneider and Frost (1996) most patterns, which in fact likely contributed in Wisconsin, Euliss et al. (1999) in North Da- to detection of relationships that were statisti- kota, Brooks (2000) in Massachusetts, and Fair- cally significant but explained only a minimal child et al. (2003) in Pennsylvania have all tout- portion of variation. a-levels for individual tests ed the importance of hydroperiod variation to are often reduced to account for repeated anal- invertebrates. However, those studies addressed yses, a practice questioned by Perneger (1998). extreme contrasts in hydroperiod. For example, If we had reduced a, even fewer of the univar- of the 7 ponds studied by Schneider and Frost iate relationships detected in our study would (1996), 1 was essentially permanent, whereas 2 have remained significant, thus exacerbating the others flooded for only 1 to 3 wk per year. Ex- pattern of nonconcordance between macroinver- tremes in weather also affect hydroperiods and tebrate and environmental variables. The CCA invertebrates in seasonal ponds. Euliss et al. 20041 MACROINVERZBMESIN SEASONAL WmDLAND PONDS 63

(1999) and Sehneider (1999) both discussed how es, limnephilids) that would be expected to re- drought could induce major shifts in wetland spond to litter supplies were not associated with invertebrate communities, and Golladay et al. variables related to forest condition, whereas (1997) reported that unusually wet conditions certain predators (dytiscids, hydrophilids), de- could do the same. Gross differences in hydro- spite lacking a direct relationship, were influ- period should remain a defining feature to mac- enced by these variables. Particularly perplexing roinvertebrates, which can explain faunal differ- were negative relationships between litter input ences among varying classes of aquatic and wet- and macroinvertebrate taxon richness and the land habitat (Wellborn et al. 1996). However, de- relative abundances of some taxa. Leaf detritus spite high variation in hydroperiod among our was the most abundant food resource in ponds. study ponds, it was probably still insufficient to Macroinvertebrate abundance and diversity in influence most resident invertebrates. streams decline as leaf litter resources become Variation in water chemistry, surprisingly did limiting (Richardson 1991, Wallace et al. 1997). not affect macroinvertebrate taxon richness, and In seasonal woodland ponds, however, litter it influenced relative abundance of only a few may be so abundant that macroinvertebrate de- of the 18 widespread taxa (Table 4). As with hy- tritivores rarely become food limited. Perhaps droperiod, water chemistry extremes among the negative relationship observed between wetland ponds can affect macroinvertebrate dis- macroinvertebrate richness and litter input was tributions (Euliss et al. 1999). However, variation related to some harmful aspect of high litter in chemical conditions among our study ponds, abundance, such as increased biological oxygen despite differences as great as 2 orders of mag- demand (Battle and Golladay 2001). nitude, appeared insufficient to influence most macroinvertebrates. We suspect that most resi- Cause of variation in tnacroinwtebrates in seasonal dent macroinvertebrates of Minnesota seasonal woodland ponds woodland ponds are capable of tolerating the natural range of water chemistry variation. Wetland ecologists have been impressed with Pond hydrology and chemistry may vary an- the highly variable nature of hydroperiods, wa- nually. However, the geology and basin mor- ter chemistries, and other habitat characteristics phology (size) of ponds remains essentially con- in seasonal ponds, and they often have assumed stant. Thus, natural and consistent differences that such variation controls the equally variable in geomorphology, as indicated by glacial land- macroinvertebrate communities. However, even form and pond size, might exert significant in- with an extensive data set including a large fluences on macroinvertebrate communities. number of seasonal woodland ponds and many However, only a few (and weak) relationships habitat measures, we were able to explain only were detected between pond size and macro- a small portion of the natural variation in mac- invertebrates, and our prediction was not sup- roinvertebrate richness and abundance among ported (but see caveats in Results section). Al- ponds. Numerous studies in wetlands have though relative abundances of some macroin- failed to find compelling relationships between vertebrates differed between the 2 watersheds invertebrates and the physical environment and dytiscid relative abundance varied among (Battle and Golladay 2001, Tangen et al. 2003, landforms, mechanisms for these differences see reviews in Batzer and Wissinger 1996 and elude us. Perhaps the greatest influence of land- Batzer et al. 1999), yet few authors acknowledge form was that the density of ponds was highest that weak relationships are to be expected. Wet- in the ground moraine, with this landform thus land invertebrates probably must endure high providing more habitat for macroinvertebrates. habitat variation frequently and thus have be- Like geomorphology, influences of vegetative come tolerant to it; environmental variation may characteristics on macroinvertebrates should re- therefore not negatively affect many taxa in sea- main consistent from year to year. Several as- sonal ponds (Williams 1996). sociations were detected between macroinver- Existing hypotheses seem useful only for ex- tebrates and trees (canopy cover, basal area, lit- plaining gross patterns in macroinvertebrate ter input, CWD). However, the ecological sig- community structure among seasonal ponds, nificance of these relationships was not obvious. elucidating differences between seasonal ponds Detritivores (mollusks, non-Tanypodinae midg- and other kinds of habitat, or explaining why [Volume 23 certain taxa do poorly in seasonal ponds. Such southwest Georgia. Journal of Freshwater Ecology hypotheses are less suitable for explaining the 18:189-207. ecology of rnacroinvertebrates in individual BATZER,D. P. 1995. Aquatic macroinvertebrate re- ponds or in complexes of seasonal ponds lack- sponse to short-term habitat loss in experimental pools in Illtailand. Pan-Pacific Entomologist 71: ing extreme variation, or for interpreting the a.n2 "a "". natural variation of common organisms. Most BATZER,D. P., C. R. JACKSON,AND M. MOSNER.2000. successful macroinvertebrates in ponds may be Influences of riparian logging on plants and in- habitat generalists (Danks and Rosenberg 1987, vertebrates in small, depressional wetlands of Euliss et al. 1999, Tangen 2003), and thus their Georgia, U.S.A. Hydrobiologia 441:123-132. variation among or within ponds might be BATZER,D. P., R. B. RADER,AND S. A. WISSINCER(ED- largely stochastic. Alternatively, distinct pat- ITORS).1999. Invertebrates in freshwater wetlands terns in richness and relative abundance of mac- of North America: ecology and management. roinvertebrates might exist, but may be driven John Wiley and Sons, New York. by unstudied factors. br example, patterns of BATZER,D. I?, A. S. SHURTLEFF,AND R. B. RADER.2001. Sampling invertebrates in wetlands. Pages 339- colonization, especially those of flying insects, 354 in R. B. Rader, D. I? Batzer, and S. A. Wissin- might be as important an influence on assem- ger (editors). Bioassessment and management of blage structure as interactions within an indi- North American freshwater wetlands. John Wiley vidual pond (Batzer 1995). In our study, most of and Sons, New York. the explainable variation occurred for aquatic in- BATZER,D. P., AND S. A. WISSINGER.1996. Ecology of sects, which because of flight can choose ponds insect communities in nontidal wetlands. Annual to colonize. Flightless forms (mollusks, annelids, Review of Entomology 41 :75-100. crustaceans) must endure whatever conditions BROOKS,R. T. 2000. Annual and seasonal variation and develop, and they probably have evolved a du- the effects of hydroperiod on benthic macroin- rability that makes them little affected by habitat vertebrates of seasonal forest ("vernal") ponds in central Massachusetts, USA. Wetlands 20:707- variation. We may need to explore new research 71E directions, rathe; than continue using the tactic / LJ. CAMPEAU,S., H. R. MURKIN,AND R. D. TITMAN.1994. of simply defining fundamental niche con- Relative importance of algae and emergent plant straints, to understand the ecology of macroin- litter to freshwater marsh invertebrates. Canadian vertebrates in seasonal ponds. Journal of Fisheries and Aquatic Sciences 51:681- 692. CHEAL,F., J. A. DAVIS,J. E, GROWNS,J. S. BRADLEY, Acknowledgements AND F. H. WHI~ES.1993. The influences of sampling method on the classification of wetland We thank Kory Cease, Leanne Egeland, macroinvertebrate communities. Hydrobiologia Dwight Streblow, Amy Braccia, Sally Entrekin, 257:47-56. and Susan Dietz-Brantley for field and labora- CHIPPEWANATIONAL FOREST. 1996. Landtypes of the tory assistance, and Sally Entrekin, Susan Dietz- Chippewa National Forest. Internal Report. Chip- Brantley Erika Bilger Kratzer, and anonymous pewa National Forest, USDA Forest Service, Cass referees for useful comments of earlier versions Lake, Minnesota. (Available from: Chippewa Na- of the manuscript. This research was supported tional Forest, USDA Forest Service, Cass Lake, by funds from the USDA brest Service, North Minnesota 56633 USA.) Central Research Station, and the University of DANKS,H. V, AND D. M. ROSENBERG.1987. Aquatic Georgia Hatch Program. insects of peatlands and marshes in Canada: synthesis of information and identification of needs for research. Memoirs of the Entomological Soci- Literature Cited ety of Canada 140:163-174. EBERT,T. A., AND M. L. BALKO.1987. Temporary pools BAILEY,R. C., R. H. NORRIS,AND T. B. REMVOLDSON. as islands in space and time: the biota of vernal 2001. Taxonomic resolution of benthic macroin- pools in San Diego, Southern California, USA. Ar- vertebrate communities in bioassessments. Jour- chiv fiir Hydrobiologie 110:lOl-123. nal of the North American Benthological Society ENTREKIN,S. A., S. W. GOLLADAY,AND D. P. BATZER. 20:280-286. 2001. The influence of plant community on chi- BAT~LE,J., AND S. W. GOLLADAY.2001. Water quality ronomid secondary production in two wetland and macroinvertebrate assemblages in three types types: cypress-gum swamps and grass-sedge of seasonally inundated hesink wetlands in marshes. Archiv fiir Hydrobiobgie 152:369-394. 20041 MACRO~RTEBRATESIN SEASONAL WOODLAND PONDS 65

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APPENDIX.Macrohvertebrates collected from 66 seasonal woodland ponds in northern Minnesota. Sampling was conducted in mid May and late June, 1998 and 1999. Individual samples consisted of pooled contents of three 1 m D-frame net sweeps. Numbers represent relative abundance (t-1 SE) per pond sample. Relative abundances are presented ody for higher taxa (e.g., families, subfamilies), but the most commonly collected genera for most groups are listed in order of relative abundance. Asterisks indicate that a macroinvertebrate was encountered on that date, but C0.1 organism per sample was collected. No entry = not collected.

- pp 11-22 May 1998 17-25 June 1998 11-18 May 1999 16-23 June 1999 Platyhelminthes Tricladida 0.8 (0.3) 0.6 (0.6) 0.6 (0.3) Nematoda 1.0 (1.0) Mollusca Gastropoda Lyrnnaeidae 3.7 (1.1) Stagnicola Physidae 6.4 (1.5) Aplexa Physella Planorbidae 12.2 (2.7) Gyraulus Promemtus Bivalvia Sphaeriidae Sphaerium Annelida Oligochaeta Lumbriculidae 29.2 (9.9) 48.9 (17.4) Lumbricidae 4.0 (1.7) Hirudinea Erpobdeltidae 1.3 (0.5) 0.5 (0.2) Glossiphoniidae 0.4 (0.1) 0.8 (0.2) Arthropods Cladocera Daphniidae 28.7 (6.7) 57.6 (14.3) C'aphia Anostraca Chirocephalidae 0.2 (0.2) 2.6 (1.0) Eubranchipus Conchostraca Lynceidae 2.5 (1.1) 2.4 (1.0) 46.1 (16.2) Lgnceus Notostraca Triopsidae X- e e Triops 20041 ~CROINVERTEBRATESIN SEASONAL WOODLAND PONDS

APPE~WIX.Conkued.

11-22 May 1998 17-25 June 1998 11-18 May 1999 16-23 June 1999 Ostracoda Cyprididae Acarina Hydrachnida Ephemeroptera Odonata Coenagrionidae Nehalennia Les tidae Les fes Libellulidae Sympetrum Hemiptera Corixidae Belos tomatidae Gerridae Notonec tidae Notomcta Pleidae Neoplea Trichoptera Hydrop tilidae Lep toceridae Oecet is Limnephilidae Limvhilus Polycentropodidae Lepidoptera Pyralidae Coleoptera Gyrinidae Haliplidae Haliplus Dytiscidae Hyd roporus Acilius Dyt iscus H ydrophilidae Berosus Tvopisternus Scir tidae Staphylinidae Diptera Ceratopogonidae Forupomyiinae Ceratopogoninae Chaoboridae Mochlqx Chaobortrs Chironomidae Chironominae / Or thocladinae Chirommus Poiy pedilum D. P. BATZER ET AL.

APPE~IX.Continued.

11-22 May 1998 17-25 June 1998 11-18 May 1999 16-23 June 1999 Tanypodinae Larsia Psecfrotaqpus C ulicidae Aedes Culex Anopheles Dixidae Dixella Tipulidae Ephydridae Stratiomyiidae Syrphidae Tabanidae