Hydrobiologia 497: 161–167, 2003. © 2003 Kluwer Academic Publishers. Printed in the Netherlands.

161

Distribution and abundance of macroinvertebrates within two temporary ponds Geoffrey R. Smith, David A. Vaala & Haley A. Dingfelder Department of Biology, Denison University, Granville, OH 43023 U.S.A. Tel: [+1]-740-587-6374. Fax: [+1]-740-587-6417. E-mail: [email protected] Received 8 July 2002; in revised form 14 February 2003; accepted 3 March 2003

Key words: abundance, bivalves, distribution, hemipterans, odonates, snails

Abstract We investigated the distributions of macroinvertebrates within two temporary ponds (Spring Peeper Pond and Taylor-Ochs Pond) in central Ohio and examined what environmental factors may be driving those distributions. We sampled macroinvertebrates in Spring Peeper Pond three times from May to July 2001, and Taylor-Ochs Pond two times from May to June 2001. Macroinvertebrate distributions were significantly aggregated on all sampling dates in both ponds. Bivalve abundance in Spring Peeper Pond was higher in shallower water. The distribution of bivalves in Taylor-Ochs Pond was not correlated with any variable we measured. Dragonfly nymph abundance in Taylor-Ochs Pond decreased between the first and second sampling dates, whereas in Spring Peeper Pond no factor examined was correlated with dragonfly nymph density. Snail densities in Spring Peeper Pond were negatively related to dissolved oxygen and depth. In Taylor-Ochs Pond, snail abundance was positively related to temperature. The densities of damselfly nymphs in Spring Peeper Pond were positively related to dissolved oxygen and depth and declined across the study. In Spring Peeper Pond, hemipteran densities were negatively related to depth and increased across the study. Damselfly nymphs and hemipterans were not common enough in Taylor-Ochs to analyze. In general, the abiotic and biotic factors we examined explained relatively little (<37% in all cases) of the within pond distribution of the macroinvertebrates in our two study ponds.

Introduction Several studies have considered the factors affecting macroinvertebrate distributions among ponds. For example, the presence or absence of fish or other predators (e.g., crayfish, newts) in a pond appears to be important in determining the abundance of macroinvertebrates (Mallory et al., 1994; Nyström et al., 1996; Smith et al., 1999; Zimmer et al., 2001). Water chemistry, such as pH, dissolved oxygen, etc., has also been shown to determine the distribution of macroinvertebrates among ponds (Van Someren, 1946; Pip, 1986; Vivar et al., 1996). Hydroperiod and habitat characteristics of a pond (e.g., depth, surrounding vegetation, pond area) can also influence which macroinvertebrates occur in it (Downie et al., 1998; Moore, 2001; Oertli et al., 2002).

In contrast, relatively few studies have addressed what factors affect within-pond distributions of macroinvertebrates. Many past studies have focussed on the importance of macrophytes in determining macroinvertebrate distributions within a pond (Cheruvelil et al., 2000, 2002; Weatherhead & James, 2001; Waters & San Giovanni, 2002), potentially because of their role in food availability or as a refuge from predators (Bennett & Streams, 1986; Gilbert et al., 1999). Other studies have found correlations of macroinvertebrate distributions within ponds or lakes with depth or sediment type of the bottom (Wissinger, 1988; Bailey, 1989; Biswas & Raut, 1999). However, some studies have found little or no relationship between macroinvertebrate distributions and any environmental factor, such as macrophyte distribu-

162 tion, physical characteristics, or local water chemistry (Hurley et al., 1995). We investigated the distribution of macroinvertebrates within two fishless, temporary ponds in central Ohio, U.S.A. We were particularly interested in determining if various physical and biotic characteristics (water depth, dissolved oxygen, water temperature, presence or absence of macrophytes) could explain variation in macroinvertebrate abundance within these two ponds. We also investigated how macroinvertebrate distributions and abundances changed between sampling dates.

Study sites The two small, temporary ponds we investigated, Spring Peeper Pond and Taylor-Ochs Pond, are located on the Denison University Biological Reserve, Licking County, Ohio, U.S.A. (see Table 1 for pond characteristics for each sampling date; see also Schultz & Mick, 1998 for more details of the two ponds). In a typical year, Spring Peeper Pond dries up in late August or early September. In contrast, Taylor-Ochs Pond is usually dry by the end of July. Both ponds are supplied by springs and by run-off and typically refill with fall rains (late September and October). Because of their temporary nature, both ponds are fishless. nearby (<1 km) permanent ponds (both fishless and with fish) and small streams may provide sources of recruits for the macroinvertebrate populations in these ponds. The bottoms of both ponds are primarily muddy and were homogeneous throughout.

Materials and methods

imum |r| = 0.361, mean |r| = 0.216), and Spring Peeper Pond (maximum |r| = 0.389, mean |r| = 0.164). To sample the macroinvertebrates in each pond we established a sampling grid with points separated by 10 m along the longer axis of each pond, and 5 m along the shorter axis of the pond. We used the same grid for each sampling date. At each point of the sampling grid we used a single sweep of a 0.39 m × 0.30 m net (mesh = 3 mm) to sample macroinvertebrates. The size of the net mesh means smaller taxa were likely underrepresented. Each sweep was 1 m long. In all sweeps, vegetation in the sweep volume was sampled as well as the water column, with sampled vegetation carefully searched for macroinvertebrates. Our sweeps only sampled the top 1 – 2 cm of the pond bottom. We were unable to detect any effect of sampling sweeps when we visited the ponds for subsequent sampling periods. We identified and counted the macroinvertebrates collected in each sample. Macroinvertebrates were identified to the most practical taxonomic level in the field if numbers permitted; however, if numbers of invertebrates was very high, samples were returned to the lab and refrigerated until samples could be processed (typically <24 h after sampling). Samples were returned to the pond after sampling. At each sampling site we measured dissolved oxygen and water temperature (in the middle of the water column using a YSI 95 Dissolved Oxygen Meter), depth of the water (to nearest 0.005 m using a meter stick), and noted the presence (i.e., >10% of sweep path) or absence of any macrophytes (emergent or submergent). Abiotic factors were measured 24 h after biotic sampling. All abiotic measurements for a particular pond were made within a 2 h period coinciding with the sampling period for the biotic samples.

Sampling methods Statistical analyses We sampled macroinvertebrates and measured abiotic variables on two dates (31 May and 21 June 2001) in Taylor-Ochs Pond (pond dried up in early July), and on three dates (29 May, 19 June, and 10 July 2001) in Spring Peeper Pond. For some analyses, we include data from all sampling dates for each pond. We are assuming that, because of changes in the pond (e.g., pond drying) and time between samples (3 weeks), the samples at each sampling site on each date are independent. This assumption is supported by low correlations (r) among the abundances of individual taxa between sampling dates in Taylor-Ochs Pond (max-

In order to analyze the abundance data, we converted raw abundances to densities by dividing the number of each taxon sampled in a sweep by the volume of water sampled by the sweep. Thus when discussing the results we will refer to macroinvertebrate densities. We also limited our statistical analyses to the most abundant and widely distributed taxa (i.e., those taxa found in >3 sweeps on every sampling date). We examined the patchiness or clumped nature of each macroinvertebrate taxon in each pond for each sampling date using the Standardized Morisita In-

163 Table 1. Characteristics of the two temporary ponds studied on each of the sampling dates. Means are given ± 1 SE, range in parentheses

Spring Peeper Pond Number of Sites with Water Percent Dry Sampling Sites Surface Area (m2 ) Mean Depth (m) Mean Water Temperature (◦ C) Mean Dissolved Oxygen (mg l−1 ) Sites with Macrophytes

Taylor-Ochs Pond Number of Sites with Water Percent Dry Sampling Sites Surface Area (m2 ) Mean Depth (m) Mean Water Temperature (◦ C) Mean Dissolved Oxygen (mg l−1 ) Percent of sites with Macrophytes

29 May 2001

19 June 2001

10 July 2001

33 0 1075 0.360 ± 0.028 (0.060 – 0.645) 20.5 ± 0.30 (16.1 – 24.5) 7.89 ± 0.46 (2.04 – 13.51) 75.8%

31 6.1% 1025 0.313 ± 0.029 (0.060 – 0.650) 22.2 ± 0.41 (19.3 – 32.8) 1.72 ± 0.16 (0.50 – 4.84) 93.5%

20 39.4% 600 0.212 ± 0.023 (0.070 – 0.450) 22.5 ± 0.36 (18.8 – 26.1) 3.90 ± 0.79 (0.44 – 14.25) 65%

31 May 2001

21 June 2001

12 July 2001

21 0 650 0.356 ± 0.029 (0.050 – 0.550) 14.9 ± 0.06 (14.6 – 15.8) 5.89 ± 0.34 (4.40 – 9.59) 81.0%

17 19.0% 500 0.205 ± 0.025 (0.070 – 0.360) 21.1 ± 0.07 (20.6 – 21.7) 1.09 ± 0.28 (0.35 – 5.31) 58.8%

0 100% 0 –

dex (see Krebs, 1989). Basically, any index of >0.5 indicates a significantly clumped distribution. Each pond was analyzed separately. To determine which of the abiotic variables were related to macroinvertebrate densities, we used stepwise regressions. For each stepwise regression, we used dissolved oxygen, depth, temperature, macrophyte presence, and sample date as the potential independent variables. We ran a separate stepwise regression for each macroinvertebrate taxon. To explore temporal changes in macroinvertebrate abundances, we ran non-parametric tests (Mann–Whitney U or Kruskal–Wallis tests) with sampling date as the independent variable for each macroinvertebrate group. Means are given ± 1 SE. Results Spring Peeper Pond We found 5 taxa of macroinvertebrates that were common enough to analyze: bivalves, dragonfly nymphs,

– – –

damselfly nymphs, snails, and hemipterans. Mean densities for each species for all sampling dates pooled, and for each sampling date individually are given in Table 2. Other taxa encountered and their mean overall density are also included in Table 2. All taxa were significantly clumped on all sampling dates (Table 3) Bivalve density decreased with the depth of the sampling site (Table 4). The density of dragonfly nymphs was unrelated to all of the variables entered into the analysis (Table 4). Damselfly nymph densities were related to three variables: oxygen (+), depth (+), and sampling date (-) (Table 4). Snail density was negatively related to oxygen and depth (Table 4). Hemipteran density was negatively related to depth and positively related to sampling date (Table 4). Bivalve density did not change significantly over the three sampling dates (Table 2; H2 = 3.64, P = 0.16). Dragonfly nymph densities remained steady across all three sampling dates (Table 2; H2 = 0.83, P = 0.66). Snail density peaked on 19 June with

164

Table 2. Mean densities (number per m3 ) of the invertebrate taxa found in Spring Peeper Pond for the entire study period, and for each of the sampling dates individually. Taxa are given in order of mean overall density. Taxa analyzed in the text are indicated by an ∗. Means are given ± 1 SE, range in parentheses Total (N = 84)

29 May 2001 19 June 2001 10 July 2001 (N = 33) (N = 31) (N = 20)

Snails∗

431.2 ± 68.0 202.1 ± 38.0 764.7 ± 155.8 (0 – 4267) (0 – 1093) (0 – 4267) 297.0 ± 61.1 173.5 ± 80.0 468.9 ± 128.4 Bivalves∗ (0 – 2620) (0 – 2185) (0 – 2620) 15.3 ± 5.9 Damselfly 39.8 ± 7.6 85.0 ± 15.6 (0 – 333.3) (0 – 333.3) (0 – 160.7) nymphs∗ 5.2 ± 5.2 9.9 ± 5.2 Nematodes & 8.9 ± 3.2 non-leech (0 – 171.9) (0 – 171.9) (0 – 115.4) Annelids 6.8 ± 1.9 6.9 ± 2.6 Dragonfly 6.3 ± 1.3 (0 – 76.9) (0 – 37.0) (0 – 76.9) nymphs∗ 5.3 ± 1.1 1.7 ± 0.8 4.3 ± 1.6 Hemiptera∗ (0 – 37.9) (0 – 16.7) (0 – 37.9) 1.7 ± 1.7 4.6 ± 1.9 Crayfish 2.9 ± 1.0 (0 – 55.6) (0 – 55.6) (0 – 41.7) 3.4 ± 1.8 3.4 ± 1.8 Leeches 2.7 ± 1.0 (0 – 55.6) (0 – 55.6) (0 – 41.7) 1.8 ± 0.9 0 Beetles 0.7 ± 0.4 (0 – 19.8) (0 – 19.8)

292.0 ± 83.0 (15.6 – 1500) 234.4 ± 79.5 (0 – 1500) 2.92 ± 1.67 (0 – 31.25) 13.5 ± 6.5 (0 – 113.6) 4.3 ± 2.0 (0 – 30.3) 12.8 ± 2.9 (0 – 31.2) 2.4 ± 1.9 (0 – 23.8) 0.5 ± 0.5 (0 – 10.0) 0

Table 3. Standardized Morisita Index values (see Krebs, 1989) for macroinvertebrate taxa in the two temporary ponds for each sampling date. A value of >0.5 indicates significant clumping or aggregation

signficantly lower densities observed on 29 May and 10 July (Table 2; H2 = 14.9, P = 0.0006). Damselfly nymph densities decreased steadily across the three sampling dates with substantially more nymphs found on 29 May than on the other two dates (Table 2; H2 = 28.0, P < 0.0001). Hemipteran densities increased dramatically across the three sampling dates with significantly more hemipterans found on 10 July than the other two sampling dates (Table 2; H2 = 9.8, P = 0.007). Taylor-Ochs Pond We found only three taxa of macroinvertebrates in sufficient numbers to analyze: bivalves, dragonfly nymphs, and snails. Mean densities for each species for all sampling dates pooled, and for each sampling date individually are given in Table 5. Other taxa encountered and their mean overall density are also included in Table 5. All analyzed taxa had significantly aggregated distributions (Table 3). Bivalve densities were not related to any of the variables entered into the stepwise regression (Table 4). Dragonfly nymph density decreased between the two sampling dates (Table 4). Snail density was positively related to temperature (Table 4). Bivalve density increased significantly between sampling dates (Table 5; Z = −2.48, P = 0.01). Dragonfly nymph density decreased 75% from the first sampling date (31 May) to the second sampling date (21 June) (Table 5; Z = −2.70, P = 0.007). Mean snail density nearly tripled between 31 May and 21 June (Table 5; Z = −2.80, P = 0.005).

29 May 2001 19 June 2001 10 July 2001 Spring Peeper Pond Bivalves Dragonfly nymphs Damselfly nymphs Snails Hemipterans

Discussion 0.606 0.535 0.517 0.518 0.606

0.537 0.566 0.572 0.521 0.564

31 May 2001 21 June 2001 Taylor-Ochs Pond Bivalves Dragonfly nymphs Snails

0.686 0.533 0.522

0.561 0.645 0.518

0.557 0.594 0.652 0.540 0.523

In general, Spring Peeper Pond had higher densities of all taxa than did Taylor-Ochs Pond. In addition, the composition of the macroinvertebrate assemblages differed between these two ponds (see Tables 2 and 5). Mean densities for macroinvertebrates in both ponds were much lower than the maximum densities we observed, sometimes by more than an order of magnitude, suggesting that some locations had few or no individuals, whereas other locations had very high densities of individuals. Indeed, all macroinvertebrate distributions we analyzed were significantly clumped (see Table 3). Other studies of freshwater macroinvertebrates have found similar patchiness within ponds. Gilbert et al. (1999) found that the notonectid (Anisops

165 Table 4. Relationships between macroinvertebrate densities and abiotic variables and sampling date (see text) in the two temporary ponds as determined by stepwise regression N

r2

P

Final Regression Model

Spring Peeper Pond Bivalves Dragonfly nymphs Damselfly nymphs

84 84 84

0.12

0.0012

0.364

<0.0001

Snails

84

0.171

0.0005

Hemipterans

84

0.28

<0.0001

674.1 – 1222.5(depth) none 29.2 + 4.6(oxygen) + 113.7(depth) −24.8(sampling date) 924.7 – 46.4(oxygen) −900.2(depth) 4.6 – 20.8(depth) + 3.8(sampling date)

Taylor-Ochs Pond Bivalves Dragonfly nymphs Snails

38 38 38

0.134 0.196

0.024 0.0054

Table 5. Mean densities (number per m3 ) of the invertebrate taxa found in Taylor-Ochs Pond for the entire study period, and for each of the sampling dates individually. Taxa are given in order of mean overall density. Taxa analyzed in the text are indicated by an ∗ . Means are given ± 1 SE, range in parentheses

Bivalves∗ Snails∗ Dragonfly nymphs∗ Nematodes & non-leech Annelids Damselfly nymphs Diptera larvae Hemiptera Beetles Leeches

Total (N = 38)

31 May (N = 21)

21 June (N = 17)

101.1 ± 32.0 (0 – 863.6) 95.8 ± 15.5 (0 – 416.7) 8.2 ± 2.1 (0 – 68.2) 8.2 ± 3.7 (0 – 109.4)

67.6 ± 41.3 (0 – 863.6) 58.8 ± 12.6 (0 – 241.7) 12.4 ± 3.3 (0 – 68.2) 0

142.5 ± 49.8 (0 – 795.5) 141.7 ± 27.5 (0 – 416.7) 2.9 ± 1.7 (0 – 22.7) 18.4 ± 7.8 (0 – 109.4)

5.4 ± 1.7 (0 – 41.7) 4.2 ± 2.9 (0 – 98.5) 1.9 ± 1.3 (0 – 50.0) 0.8 ± .6 (0 – 22.7) 0.5 ± 0.5 (0 – 20.8)

7.6 ± 2.7 (0 – 27.8) 4.7 ± 4.7 (0 – 98.5) 3.5 ± 2.4 (0 – 50.0) 0.4 ± 0.4 (0 – 8.3) 0

2.6 ± 1.8 (0 – 27.8) 3.7 ± 3.3 (0 – 55.6) 0 1.3 ± 1.3 (0 – 22.7) 1.2 ± 1.2 (0 – 20.8)

none 21.8 – 9.45(sampling date) −143.1 + 13.5(temperature)

wakefieldi) occurred in aggregations, thus creating a great deal of variation in density estimates. Fukuhara & Nagata (1995) also found patchy distributions of freshwater mussels (Anodonta woodriana) in a small pond. Brown & DeVries (1985) found that adult snails had clumped distributions in both a permanent pond and a temporary pond. The patchiness of individuals within a pond has consequences for intraspecific and interspecific interactions. For example, if we only consider mean densities we might greatly underestimate the potential for competition, predation, or parasitism (or any other density-dependent factor) to be important. It also suggests that individuals within the same population can experience greatly different levels of density-induced effects. The patchiness in density described above begs the question “What explains the patchiness?” In other words, why do more individuals occur in some locations than in others? There is no general answer to these questions for the macroinvertebrates we found, and so we will address each group in turn. Bivalve abundance in Spring Peeper Pond was higher in shallower water, but no such relationship was found in Taylor-Ochs Pond. Indeed the distribution of bivalves in Taylor-Ochs Pond was not correlated with any variable we measured. For freshwater mussels, Biswas & Raut (1999) found that depth is important in explaining within pond distributions, with juveniles preferring the shallows and older individuals occurring in deeper water. Other studies have shown other

166 factors affect the distribution of bivalves. For example, dissolved oxygen has been found to be important in the distribution of bivalves, both within and among ponds (Pip, 1986; Biswas & Raut, 1999). Weatherhead & James (2001) found that substrate type, macrophyte biomass, and the amount of detritus were important in bivalve distributions. Snail densities in Spring Peeper Pond were found to be negatively related to dissolved oxygen and depth. In Taylor-Ochs Pond, snail abundance was positively related to temperature. Other studies have shown that dissolved oxygen is an important factor explaining the distributions of snails, both positively (e.g., Van Someren, 1946) and negatively (e.g., Hurley et al., 1995). Vivar et al. (1996) observed greater abundances of snails in shallow water compared with deeper water. Weatherhead & James (2001) found that substrate particle size affected snail distributions with finer substrates supporting larger numbers of snails. Some snail distributions are determined by the distribution of macrophytes (Lodge, 1985; van den Berg et al., 1997; Weatherhead & James, 2001). Hurley et al. (1995) found no correlation between physical or chemical variables and the distributions of two freshwater snails (Austropeplea lessoni and Amerianna carinata) in a large reservoir. Dragonfly nymph abundance in Taylor-Ochs Pond decreased between the first and second sampling dates, whereas in Spring Peeper Pond no factor examined was correlated with dragonfly nymph density. The densities of damselfly nymphs in Spring Peeper Pond were positively related to dissolved oxygen and depth and declined across the study. Damselflies were not abundant enough in Taylor-Ochs to analyze statistically. A decline in nymph density over time for dragonflies in Taylor-Ochs Pond and for damselflies in Spring Peeper Pond probably reflects the emergence of dragonflies in the period between samples. No decline was apparent in dragonflies in Spring Peeper Pond, perhaps because additional dragonflies may have oviposited in the pond since it retained water longer. In addition, recruitment into Spring Peeper Pond may be higher and more continuous since it is closer to potential sources of recruits than is Taylor-Ochs Pond. Why this is not true for damselflies needs further investigation. Zimmer et al. (2001) found that dragonfly nymph abundances were highest in early and midSummer, with lower abundances at other times. Smiley & Tessier (1998) found that sampling date had an effect on Enallagma spp. Abundance; however, they found more in the fall than the summer which contrasts

with our observation of a decrease across the summer. In other studies, depth has been identified as an important factor in explaining odonate distributions, with more occurring in shallower water (Wissinger, 1988; Smiley & Tessier, 1998; Zimmer et al., 2001), perhaps as a consequence of greater food availability (Thurnheer & Reyer, 2001). Odonate abundance is often greater with increasing macrophyte biomass and detrital abundance (Weatherhead & James, 2001; Tarr & Babbitt, 2002). In Spring Peeper Pond, hemipteran densities were negatively related to depth and increased across the study. Hemipterans were not common enough in Taylor-Ochs Pond to analyze. As in our study, Zimmer et al. (2001) found hemipterans tended to be more abundant in shallow to mid-depth, and lowest in deep regions. Gilbert et al. (1999) found that Anisops wakefieldi, a notonectid, was found along the shore during the day if large, but along the shore and in the open water small. Zimmer et al. (2001) also found the peak of hemipteran abundance to be late summer, again similar to our results. In contrast to our results, Bennett & Streams (1986) found that two species of Notonecta used depth randomly with respect to availability. Notonecta lunata in a fish pond were associated with macrophytes, whereas N. undulata in a fishless pond only used macrophyte habitats during early instars (Bennett & Streams, 1986). In general, the abiotic and biotic factors we examined explained relatively little (<37% in all cases) of the within pond distribution of the macroinvertebrates in our two study ponds. Other factors, not measured by us, may be important in determining the distributions of these macroinvertebrates. First, sediment type or size may be important (Bailey, 1989; Weatherhead & James, 2001). For our two study ponds we doubt this could account for much of the unexplained variation in macroinvertebrate abundances because the sediment types on the bottom of these two ponds are fairly homogeneous within a pond. Second, we only considered the presence or absence of macrophytes. It could be that this obscured the importance of particular types or architectures of macrophytes for these macroinvertebrates (e.g., Lodge, 1985; Parsons & Matthews, 1995; Cheruvelil et al., 2000, 2002). Third, the distributions of these macroinvertebrates are likely influenced by the distribution of their food (e.g., Thurnheer & Reyer, 2001), whose distribution may in turn be determined by factors other than those measured here.

167 Acknowledgements Funding for this study was provided by the Denison University Research Foundation, the Howard Hughes Medical Institute, and the Sherman Fairchild Foundation. We thank P. Lorth and J. Rettig for help in counting and in identifying some of the macroinvertebrates, and S. Kaplan-Goland for his assistance in the field. The comments of three anonymous reviewers improved an earlier version of this manuscript.

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