We investigated the response of pond-breeding amphibian assemblages to wetland hydroperiod and associated predator changes (invertebrates (abundance and richness) and fish (presence/absence)) in relatively undisturbed landscapes in southern New Hampshire, U.S.A. We sampled 42 wetlands for larval amphibians in 14 spatial blocks (each with a short-, intermediate-, and permanent-hydroperiod wetland) in 1998 and 1999. Assemblages in shorthydroperiod wetlands (<4 months) were depauperate (4 species only) compared with intermediate-hydroperiod (nonpermanent but >4 months) and permanent wetlands, which included 7 and 9 species, respectively. Total amphibian abundance did not vary among hydroperiod categories. Species distributions along the hydrological gradient also differed. Rana sylvatica dominated wetlands with short and intermediate hydroperiods, whereas Rana catesbeiana, Bufo americanus, Rana clamitans, and Pseudacris crucifer dominated in those with a longer hydroperiod. Among permanent wetlands, amphibian species richness and abundance did not differ with respect to the presence of predatory fish, although there were species-compositional differences. Amphibian species richness and abundance were positively correlated with the abundance and richness of predatory invertebrates, suggesting that both amphibian and macroinvertebrate predator assemblages may be responding similarly to differences in wetland characteristics (e.g., dissolved oxygen concentration). Overall, our results indicate that wetland hydroperiod has an important influence on amphibian distribution and should be incorporated into regulations and legislation designed to protect biologically diverse isolated wetlands.Résumé : Nous avons examiné la réaction d'un peuplement d'amphibiens, qui se reproduisent dans des étangs, à l'hydropériode de terres humides et aux changements associés dans la faune des prédateurs ((abondance et richesse) des invertébrés et (présence/absence) des poissons) dans des paysages relativement peu perturbés du sud du New Hampshire, É.-U. Nous avons échantillonné les larves d'amphibiens dans 42 terres humides dans 14 blocs spatiaux (comprenant chacun une terre humide à hydropériode courte, une à hydropériode intermédiaire et une à hydropériode permanente) en 1998 et 1999. Les peuplements des terres humides à hydropériode courte (<4 mois de mise en eau) ont une faune réduite (seulement 4 espèces) en comparaison des terres humides à hydropériode intermédiaire (non permanente, mais avec >4 mois de mise en eau) ou permanente qui contiennent respectivement 7 et 9 espèces. L'abondance totale des amphibiens ne varie pas en fonction de l'hydropériode, mais la répartition des espèces change le long du gradient hydrologique. Rana sylvatica domine dans les terres humides à hydropériodes courte et intermédiaire, alors que Rana catesbeiana, Bufo americanus, Rana clamitans et Pseudacris crucifer le font dans les terres humides à hydropériode plus longue. Dans les terres humides permanentes, la richesse spécifique et l'abondance des amphibi...

T. L. 2004. The relationship between wetland hydroperiod and nestedness patterns in assemblages of larval amphibians and predatory macroinvertebrates. Á/ Oikos 107: 16 Á/27.Assemblages exhibit nested distributional patterns if the species found in species-poor locations also occur in progressively richer locations. We investigated patterns of nestedness in assemblages of larval amphibians and predatory macroinvertebrates in 42 isolated freshwater wetlands in southern New Hampshire, USA. These wetlands varied markedly in hydroperiod and we predicted that nestedness would be relatively weak because changes in disturbance processes (the relative threat of desiccation and predation) along the hydroperiod gradient often generate distinct assemblages. Contrary to expectations we found that both amphibian and macroinvertebrate assemblages were strongly nested not only with respect to species richness but also with respect to hydroperiod and wetland size, which were positively correlated. We attribute our results to the increased colonization rates and decreased extinction rates associated with increasing hydroperiod, and to concomitant increases in wetland size, habitat heterogeneity/complexity, and possibly water temperature. Moreover, the impact of predatory fishes on species richness and composition of amphibians and macroinvertebrates was relatively minor. We found that amphibians had a significantly lower degree of nestedness than macroinvertebrates, suggesting that a higher proportion of amphibian species found in species-poor assemblages was unlikely to occur in species-rich assemblages of amphibians (e.g. wood frogs and spotted salamanders). The degree of nestedness appeared to be influenced primarily by hydroperiod and wetland size for amphibians, whereas nestedness of macroinvertebrates was influenced by unknown factors (possibly water temperature) in addition to hydroperiod and wetland size. The high degrees of nestedness observed in amphibian and macroinvertebrate assemblages imply that protection of larger, more permanent wetlands may be more important for conserving native biological diversity than protection of smaller, non-permanent wetlands. However, non-permanent wetlands are used by several species of conservation concern that often do not occur in larger and more permanent wetlands.

We conducted a field study to examine the influence of hydroperiod and concomitant changes in abiotic (wetland size, pH, conductivity, dissolved oxygen and water temperature) and biotic (predatory fish presence) characteristics on macroinvertebrate communities in isolated wetlands in southern New Hampshire. Invertebrates were sampled using dipnet sweeps in 42 wetlands with short (<4 months), intermediate (4-11 months) or long (permanent) hydroperiods in 1998 and 1999. We found that invertebrate genera richness, and to a lesser degree abundance, increased linearly along the hydrological gradient, and in response to temperature and dissolved oxygen. Relative abundance of genera also differed markedly with respect to hydroperiod. Most notably, invertebrate communities changed from Acilius-dominated communities to Notonecta-dominated communities. Invertebrate relative abundances in permanent wetlands also differed with respect to the occurrence of predatory fish. Some genera (e.g., Libellula, and Dytiscus) were more likely to occur in permanent wetlands without fish, whereas other genera (e.g., Buena, and Basiaeshna) were more likely to occur in wetlands with predatory fish. Because aquatic invertebrate communities differed markedly with respect to wetland hydroperiod, and in relation to the occurrence of predatory fish, it is essential to retain a diversity of wetlands in the landscape to ensure the long-term persistence of aquatic invertebrate biodiversity.

We examined the microhabitat distribution of green frog larvae (Rana clamitans) and two common predacious insect genera at 27 wetlands in southern New Hampshire to determine if it was related to the presence of vegetation. Rana clamitans and hemipterans (Belostoma spp.) were rarely captured in non-vegetate d microhabitats. Larval odonates (Aeshna spp.) were captured more frequently in vegetated microhabitats but the difference was not signi cant. In a laboratory experiment, we tested the effects of plant density on the survival of R. clamitans larvae exposed to either Belostoma umineum or Aeshna mutata. When no cover was available, survival of R. clamitans tadpoles was very low when exposed to either predator. Belostoma umineum was a less effective predator than A. mutata, and survival rates of tadpoles did not differ between high and low plant density when exposed to this predator. In contrast, survival of tadpoles was signi cantly higher in the high density vegetation treatment compared to the low density treatment when exposed to A. mutata. Although plant structure can reduce predation on R. clamitans larvae, the level of structure necessary to signi cantly mediate predation may depend largely on the foraging mode of the predator.