Amphibian species richness across environmental gradients

Abstract

Large-scale field patterns are a fundamental source of inferences on processes responsible for variation in species richness among habitats. We examined species richness of larval amphibian communities in 37 ponds over seven years on the Univ. of Michigan's E. S. George Reserve. Ordination of the community incidence matrix indicated a strong major axis of variation in species associations that was correlated with pond hydroperiod, surface area and forest canopy cover. Communities were significantly nested with those species found in ponds with high canopy cover, small area and short hydroperiod being nested subsets of those found in ponds with contrasting characteristics. Presence of fish had strong negative effects on species richness; relaxation of this effect also was apparent when fish were extirpated from ponds by drought. We employed a model selection analysis to identify the most appropriate statistical model for predicting the long-term average species richness of these ponds from local abiotic and biotic (predator and competitor density) factors. A model including only the abiotic factors was overwhelmingly superior for the anurans; hierarchical partitioning indicated that area and canopy cover alone accounted for over 70% of the independent effects of predictor variables. The global model including both abiotic and biotic factors was the best supported model for the caudates, and correspondingly hierarchical partitioning suggested that area, hydroperiod, invertebrate predators and caudate biomass all accounted for 9 Á16% of the independent effects. Overall, biotic factors accounted for much less of the variation in species richness than abiotic factors. The patterns in larger, open-canopy ponds provided little evidence of competitive effects on species richness, though there were patterns consistent with competitive effects in small, closed-canopy ponds. The unusual temporal and spatial extent of these data enabled us to critically evaluate ideas regarding patterns in larval amphibian communities, and the effects of area, disturbance (hydroperiod) and productivity (canopy cover) on species richness of these communities. These results have important implications to the conservation of amphibian species richness in freshwater wetlands, which are among the most threatened ecosystems worldwide.Understanding processes responsible for variation in species richness among habitats is a fundamental goal of ecology, and large-scale field patterns are a fertile source for hypotheses concerning these processes. Such pattern analysis has a venerable history in ecology, in particular analyses of the distributions of both individual taxa and species richness along environmental gradients. These patterns provide inferences concerning the traits of species associated with performance differences along the gradients, and the factors affecting species coexistence and community assembly (Connell 1975, Ricklefs and Schluter 1993, Wellborn et al. 1996.Moreover, in contrast to the conduct of much of experimental ecology, suc...

Spatial and temporal dynamics of habitat selection across canopy gradients generates patterns of species richness and composition in aquatic beetles

“…Canopy coverage has been increasingly implicated in the performance, abundance, distribution, and diversity of a variety of aquatic species ( Nilsson & Svensson, 1995;Skelly et al , 1999;Grether et al , 2001;Hill et al , 2001;Halverson et al , 2003;Batzer et al , 2004;McCauley, 2005;Schiesari, 2006;Werner et al , 2007;Williams et al , 2007 ). Changes in forest cover associated with changing forestry and agricultural practices, habitat restoration efforts, and alterations of natural disturbance regimes ( Frost, 1995 ;Tilman et al , 2000;Caspersen et al , 2000;Schurbon & Fauth, 2003;Chen et al , 2006 ) may have unforeseen consequences for associated aquatic systems.…”

“…If species behaviourally avoid low-quality habitats, expected changes in population or metapopulation size can be mediated, assuming a sufficient high-quality habitat remains accessible. Documented local extinction events in closed canopy ponds ( Skelly et al , 1999;Werner et al , 2007 ) could be behavioural phenomena, depending on the strength of the avoidance or attraction. Although more work is necessary in quantifying colonisation at intermediate canopy levels, we have demonstrated that the extremes of this gradient produce strong spatial variation in colonisation dynamics, as opposed to simply generating local variation in performance and mortality.…”

“…Arranging aquatic habitats along canopy coverage gradients, from open canopies receiving high levels of solar radiation to those with closed canopies and lower productivity, has been useful for predicting the distribution and performance of numerous aquatic taxa ( Skelly et al , 1999;Werner et al , 2007 ). The general, but not exclusive, pattern has been reduced performance, abundance, and diversity of aquatic taxa in closed canopy sites ( Nilsson & Svensson, 1995;Skelly et al , 1999;Batzer et al , 2000;Hill et al , 2001;Palik et al , 2001;Halverson et al , 2003, Burne & Griffin, 2005McCauley, 2005;Werner et al , 2007 ). How modifications to the terrestrial matrix (forest loss or re-growth see Caspersen et al , 2000;Chen et al , 2006 ) affect aquatic ecosystems ( Skelly et al , 1999;Rubbo & Kiesecker, 2004 ) depends critically on how such changes affect colonisation dynamics.…”

“…generate gradients of canopy coverage surrounding freshwater habitats that correlate with variation in numerous abiotic and biotic factors in the underlying waters ( Werner & Glennemeier, 1999;Skelly et al , 2002;Batzer et al , 2004;Schiesari, 2006 ). Arranging aquatic habitats along canopy coverage gradients, from open canopies receiving high levels of solar radiation to those with closed canopies and lower productivity, has been useful for predicting the distribution and performance of numerous aquatic taxa ( Skelly et al , 1999;Werner et al , 2007 ). The general, but not exclusive, pattern has been reduced performance, abundance, and diversity of aquatic taxa in closed canopy sites ( Nilsson & Svensson, 1995;Skelly et al , 1999;Batzer et al , 2000;Hill et al , 2001;Palik et al , 2001;Halverson et al , 2003, Burne & Griffin, 2005McCauley, 2005;Werner et al , 2007 ).…”

Riqueza e distribuição temporal de anuros (Amphibia: Anura) em um fragmento de Floresta Ombrófila Mista

“…Apesar de sua importância, a determinação da composição de espécies e da diversidade em uma área podem ser difíceis de serem identificadas corretamente, dada a variação de complexidade das relações ecológicas em que cada táxon está inserido (ricKlefs & schluTer, 1993;chesson, 2000;Werner et al, 2007;GoTelli et al, 2009). No caso dos anfíbios anuros, correlações positivas têm sido encontradas tanto entre riqueza e fatores bióticos, como por exemplo, a competição direta por recursos com espécies invasoras (Pearl et al, 2004) e a predação de girinos por espécies de peixes (PillioD et al, 2010) quanto por fatores abióticos, como por exemplo a fragmentação florestal (bell & Donnely, 2006) e a heterogeneidade ambiental (Keller et al, 2009).…”