Spatiotemporal variability of abundance size-spectra in streams across North America

Accepted version of this manuscript can be found here: https://doi.org/10.1111/gcb.15862 The distribution of abundance and biomass within ecological communities is related to trophic transfer efficiency from prey to predators. While it is considered to be one of the few consistent patterns in ecology, spatiotemporal variation of this relationship across continental-scale environmental gradients is unknown. Using a database of stream communities collected across North America (18-68° N latitude, -4 to 25°C mean annual temperature) over 3 years, we constructed 162 mass-abundance relationships (i.e. size spectra). Size-spectra slopes declined (became steeper) with increasing temperature. However, the magnitude of change was relatively small, with median slopes changing from -1.2 to -1.3 across a 29°C range in mean annual temperature. In contrast, total community biomass increased 3-fold over the temperature gradient. Our study suggests strong conservation of abundance size-spectra in streams across broad natural environmental gradients. This supports the emerging use of size-spectra deviations as indicators of ecosystem health.

Trophic ecology of syntopic anurans of tropical stream communities

We investigated trophic resource partitioning in seven syntopic anurans from low- and mid-elevation stream habitats of a tropical riparian ecosystem by utilising stomach content analysis (SCA) and stable isotope analysis (SIA). Our SCA data revealed dietary similarities, narrow trophic niche breadth, and low dietary niche overlap in Ansonia muelleri, Limnonectes magnus, Occidozyga laevis, Megophrys stejnegeri, Pulchrana grandocula, Sanguirana mearnsi, and Staurois natator which could be attributed to these anurans’ selection of available local prey items. We confirmed ant-specialisation (myrmecophagy) of the Mindanao island endemic bufonid A. muelleri based on our temporal SCA dietary data. Our SIA estimates of assimilation of potential prey sources confirmed that L. magnus, P. grandocula, and O. laevis are generalist predators, opportunistically feeding on locally abundant insect prey items. This study on trophic resource partitioning in syntopic anurans provides the first picture of trophic interactions, i.e., predation and competition in stream communities in tropical riparian zones of a watershed ecosystem in northeast Mindanao of the southern Philippines.

Meta-ecosystem dynamics drive the spatial distribution of functional groups in river networks

Spatial flow of material and resources is a central process structuring ecological communities. The meta-ecosystem concept provides a theoretical framework to study the interplay between local and regional flows of resources and their implications for ecosystem dynamics and functioning. Yet, meta-ecosystem theory has been applied to highly simplified systems, and the effects of meta-ecosystem dynamics in real-world landscapes, characterized by specific spatial structures, remain largely unexplored. Here, we develop a spatially explicit meta-ecosystem model for dendritic river networks based on a highly realistic landscape matrix. By formalizing a seminal concept in freshwater ecology, we show that the spatial distributions and regional biomass of major functional groups observed in stream communities are determined by specific rates of resource flows. Overall, high rates of resource flow have a negative effect on the regional biomass of all the functional groups studied and can lead to extinctions at the meta-ecosystem scale.

Common insecticide disrupts aquatic communities: A mesocosm-to-field ecological risk assessment of fipronil and its degradates in U.S. streams

Insecticides in streams are increasingly a global concern, yet information on safe concentrations for aquatic ecosystems is sparse. In a 30-day mesocosm experiment exposing native benthic aquatic invertebrates to the common insecticide fipronil and four degradates, fipronil compounds caused altered emergence and trophic cascades. Effect concentrations eliciting a 50% response (EC50) were developed for fipronil and its sulfide, sulfone, and desulfinyl degradates; taxa were insensitive to fipronil amide. Hazard concentrations for 5% of affected species derived from up to 15 mesocosm EC50 values were used to convert fipronil compound concentrations in field samples to the sum of toxic units (∑TUFipronils). Mean ∑TUFipronils exceeded 1 (indicating toxicity) in 16% of streams sampled from five regional studies. The Species at Risk invertebrate metric was negatively associated with ∑TUFipronils in four of five regions sampled. This ecological risk assessment indicates that low concentrations of fipronil compounds degrade stream communities in multiple regions of the United States.