No abstract

Resource subsidies of energy and nutrients can be transported via physical forces, such as gravity, wind or water and biotic processes, such as animal migration or emigration. Migratory transport of nutrient subsidies may be associated with reproductive processes, such as the deposition of eggs or emigration of juveniles to adult habitats. We quantified net nutrient fluxes associated with amphibian migrations across aquatic–terrestrial boundaries of eight temporary ponds in Illinois, USA. We measured carbon (C), nitrogen (N) and phosphorus (P) subsidies from terrestrial environments to ponds, in the form of eggs, and the reciprocal subsidies from ponds to terrestrial environments via juvenile emigration. Juvenile emergence biomass did not follow patterns of egg biomass, as not all species bred successfully in each pond, resulting in variability in the magnitude of nutrient fluxes both across ponds and species. The terrestrial environment was not always the recipient system of net nutrient fluxes. Hydroperiod, trophic interactions and species composition explained some dynamics of N and P subsidies. Anthropogenic alterations that affect amphibian communities, such as habitat fragmentation and conversion for agriculture and urbanisation, could have large‐scale impacts on nutrient fluxes and connectivity of temporary pond–forest systems.

Summary Taxonomic and functional diversity in freshwater habitats is rapidly declining, but we know little about how such declines will ultimately affect ecosystems. Neotropical streams are currently experiencing massive losses of amphibians, with many losses linked to the chytrid fungus, Batrachochytrium dendrobatidis (Bd). We examined the ecological consequences of the disease‐driven loss of amphibians from a Panamanian stream. We quantified basal resources, macroinvertebrates, N uptake and fluxes through food‐web components and ecosystem metabolism in 2012 and 2014 and compared them to pre‐decline (2006) and 2 year post‐decline (2008) values from a prior study. Epilithon biomass accrued after the decline, more than doubling between 2006 and 2012, but then decreased fivefold from 2012 to 2014. In contrast, suspended particulate organic matter (SPOM) concentrations declined continuously after the amphibian decline through 2014. Biomass of filter‐feeding, grazing and shredding macroinvertebrates decreased from 2006 to 2014, while collector–gatherers increased during the same time period. Macroinvertebrate taxa richness decreased from 2006 (52 taxa) to 2012 (30 taxa), with a subsequent increase to 51 taxa in 2014. Community respiration, which initially decreased after the amphibian decline, remained lower than pre‐decline in 2012 but was greater than pre‐decline values in 2014. Gross primary production remained low and similar among years, while NH4+ uptake length in both 2012 and 2014 was longer than pre‐decline. Nitrogen flux to epilithon increased after the decline and continued to do so through 2014, but N fluxes to fine particulate organic matter and SPOM decreased and remained low. Our findings underscore the importance of studying the ecological consequences of declining biodiversity in natural systems over relatively long time periods. There was no evidence of functional redundancy or compensation by other taxa after the loss of amphibians, even after 8 years.

No abstract

Aquatic habitats are closely linked to surrounding terrestrial systems via reciprocal subsidies. Much of the research on aquatic–terrestrial subsidies has focused on streams and lakes, while subsidies across aquatic–terrestrial boundaries of other systems, like temporary ponds, have received less attention. To address the lack of information regarding cross‐habitat subsidies of temporary ponds, we quantified leaf litter inputs, amphibian egg inputs, terrestrial insect inputs, and amphibian metamorph and aquatic insect emergence for eight temporary ponds. We compared the relative magnitude of cross‐habitat biotic subsidies of temporary ponds to identify potentially important yet overlooked subsidies. Terrestrial insect inputs to ponds were the second largest subsidy (mean 15.3 g m−2 yr−1), exceeding combined emergence of amphibians and aquatic insects (mean 4.0 g m−2 yr−1), yet these high‐quality subsidies are generally unaccounted for in similar studies. Across the wetland complex, total amphibian emergence (8929.3 g yr−1) was nearly four times higher than total aquatic insect emergence (2491.9 g yr−1). Aquatic insect emergence was similar to that of lakes and streams while amphibian emergence was generally higher. Although larger ponds produced greater total fluxes to terrestrial habitats, smaller ponds were often more productive per unit area. Therefore, a mosaic of small ponds may produce greater or equivalent subsidies to terrestrial food webs than a single large pond. Given continued threats to temporary ponds and their connections to surrounding forests, management and restoration of these systems, as well as future studies, should take holistic approaches that account for the many aquatic–terrestrial linkages, and factors that influence them.