Trophic Niche Shifts in Mountain Feirana Frogs under Human-mediated Habitat Transformations

Urbanization can induce environmental changes, disturbing habitat transformation process, and resulting in niche shift of species and local extinctions. Amphibians have experienced worldwide population declines, with ha bitat loss acting as one of the most disruptive causes. How amphibian species response to changing habitats could be reflected in their utilization and assimilation of resources. Using stable isotopes, we explored trophic niche variation between natural and transformed habitats for three closely related frog species in the genus Feirana(F. quadranus, F. taihangnica and F. kangxianensis). Our results indicated that the δ~(13)C value was negatively correlated with body size(snout-vent length) and the δ~(15)N value increased along with the ontogenetic process. The δ~(13)C values were significantly different among habitat types, and the variation of δ~(15)N values was relatively limited in different disturbed gradients. Urban groups displayed broader trophic niche width than both rural and natural groups. When species in sympatry, their resource utilization and trophic niche overlap probability were more similar in rural habitats than their natural counterparts. Our findings would be conducive to understand trophic niche and function variation in amphibians during the urbanization process, allowing for effective predictions of ecological consequences of habitat transformation. This study can also provide insight into conservation strategies for mountain amphibians in the Anthropocene.

Initial response of fish trophic niche to hydrological alteration in the upstream of Three Gorges Dam

Introduction:Damming is one of the dramatic impacts to river food webs due to habitat fragmentation and changes in the hydrological regimes.The world’s largest dam,the Three Gorges Dam(TGD),has been constructed in the middle of Yangtze River since 2003.The objective of this study was to understand the effects of altered hydrological regime on the trophic structure of fish food web along the hydrological gradient in the TGD.Methods:Fish samples were collected from an upstream,a midstream and a downstream site of the Yangtze River upstream of the TGD in May and September of 2004.Muscle tissue of each fish species was determined for stable isotopic compositions(δ^(13)C and δ^(15)N)which were used to calculate isotope-based Bayesian community-wide trophic metrics.Results:Stable isotope trophic niche analysis reveals reduced utilization of basal resource and trophic niche space at the midstream and downstream sites.By contrast,community trophic diversity and species redundancy were higher at the downstream than the upstream and midstream,likely as the result of reduced the spectrum of basal resources.These findings suggested that the negative impacts on the overall trophic niche space from reduced flow,increased water depth and stagnancy occurred only one year after the completion of the TGD.Conclusions:Altered hydrological regimes posed multiple impacts to the aquatic food web.Reduced flow and increased water depth within TGD has posed initial effects to the fish community trophic structure.Further collections ana analysis of ecological data to compare the fish trophic structure revealed in this study are needed to assess the long-term impacts of TGD on fish community structure and resources utilization.

Ontogenetic resource use and trophic dynamics of endangered juvenile Tachypleus tridentatus among diversified nursery habitats in the northern Beibu Gulf,China

Horseshoe crabs,the most well-known example of“living fossils”,are iconic and ecologically important macroinvertebrates in coastal and estuarine ecosystems.Their blood is a crucial resource for manufacturing Limulus or Tachypleus amebocyte lysate to detect bacterial endotoxins or fungal contamination in drug and medical devices.An enhanced understanding of their ecological roles and trophic interactions in the food webs is fundamental to facilitate resource management for the declining populations in Asia.Foraging information of the Asian species,however,is mainly derived from preliminary,scattered reports from a limited number of study locations.In this study,resource utilization,trophic niche dynamics,and trophic interaction of the juvenile tri-spine horseshoe crab,Tachypleus tridentatus(instars 1–12,approximately 0.5–8 years old)across ontogeny was assessed in diversified nursery habitats along the northern Beibu Gulf,China,using carbon and nitrogen stable isotopes.Our results suggest that:(i)T.tridentatus are ecological generalists given the vast range of carbon isotopic values and trophic niche width estimates exhibited between multiple instar groups;(ii)juvenile T.tridentatus across most habitat types predominantly assimilated energy from a variety of basal production sources in the food web,but primarily depended on sedimentary organic matter and seagrass resource pools;(iii)ontogenetic shifts in juvenile dietary proportions were evident,with decreased reliance on sedimentary organic matter,coupled with increased reliance on benthic macroinvertebrate grazers,detritivores,and omnivores with age;and(iv)nearly all juvenile instars occupied similar trophic positions in the food web with slight shifts in trophic position present with increasing size.Our findings indicate that resource availability and ontogenetic diet shifts strongly influence horseshoe crab trophic dynamics,and age should be accounted when formulating habitat conservation measures based on resource use for Asian horseshoe crabs.