Hydropower development in the Andean Amazon has been underestimated and will disrupt connected human and natural systems.

ABSTRACT1. Salinity tolerance is one of several important physiological attributes that determine invasion success and the pattern of dispersal of introduced aquatic organisms. Introduced freshwater fishes able to tolerate elevated salinities have the potential to invade and exploit brackish-water (mixohaline) environments and use estuaries and coastal waters as 'bridges' for dispersing from one coastal river system to another.2. Several members of the neotropical suckermouth armoured catfish genus Pterygoplichthys (Siluriformes: Loricariidae) have established non-native populations in inland waters of North and Central America, Asia and islands in the Caribbean, and Pacific and Indian oceans. Loricariids are generally considered to be strictly freshwater; but a few naturally occur in mesohaline habitats.3. Catch and habitat data from 2004-2005 and 2009-2011 fish surveys in the Grijalva-Usumacinta River delta region (south-eastern Mexico) confirmed that introduced Pterygoplichthys populations established in upstream freshwater sites (where these catfish are abundant) have recently dispersed into downstream oligohaline and mesohaline estuarine habitats. During 2009-2011 surveys, these non-native catfish -tentatively identified as P. pardalis or its hybrids -were found in sites with salinities ranging from 1 to 8 ppt (mean 5.2 ppt).4. Acute-salinity experiments were conducted with Pterygoplichthys (110-302 mm standard length, N = 140) captured in the Grijalva-Usumacinta Basin to determine upper salinity tolerance levels. Tests demonstrated that individuals maintained in salinities of 0.2 ppt were able to survive abrupt (acute) exposure to salinities up to 10 ppt with little mortality over 10 days (240 h experimental endpoint). A few individuals survived abrupt exposure to 11 and 12 ppt for 20 or more hours, although none survived more than a few hours at 16 ppt or greater.5. These field and experimental results provide quantitative evidence that non-native Pterygoplichthys are physiologically capable of surviving mesohaline conditions for extended periods and that non-native populations in Mexico are invading and presumably exploiting estuarine and other coastal environments, perhaps as feeding areas and potentially as dispersal routes.

Ecosystems vary widely in their responses to biodiversity change, with some losing function dramatically while others are highly resilient. However, generalizations about how species- and community-level properties determine these divergent ecosystem responses have been elusive because potential sources of variation (e.g., trophic structure, compensation, functional trait diversity) are rarely evaluated in conjunction. Ecosystem vulnerability, or the likely change in ecosystem function following biodiversity change, is influenced by two types of species traits: response traits that determine species' individual sensitivities to environmental change, and effect traits that determine a species' contribution to ecosystem function. Here we extend the response-effect trait framework to quantify ecosystem vulnerability and show how trophic structure, within-trait variance, and among-trait covariance affect ecosystem vulnerability by linking extinction order and functional compensation. Using in silico trait-based simulations we found that ecosystem vulnerability increased when response and effect traits positively covaried, but this increase was attenuated by decreasing trait variance. Contrary to expectations, in these communities, both functional diversity and trophic structure increased ecosystem vulnerability. In contrast, ecosystem functions were resilient when response and effect traits covaried negatively, and variance had a positive effect on resiliency. Our results suggest that although biodiversity loss is often associated with decreases in ecosystem functions, such effects are conditional on trophic structure, and the variation within and covariation among response and effect traits. Taken together, these three factors can predict when ecosystems are poised to lose or gain function with ongoing biodiversity change.

Proposed hydropower dams at more than 350 sites throughout the Amazon require strategic evaluation of trade-offs between the numerous ecosystem services provided by Earth’s largest and most biodiverse river basin. These services are spatially variable, hence collective impacts of newly built dams depend strongly on their configuration. We use multiobjective optimization to identify portfolios of sites that simultaneously minimize impacts on river flow, river connectivity, sediment transport, fish diversity, and greenhouse gas emissions while achieving energy production goals. We find that uncoordinated, dam-by-dam hydropower expansion has resulted in forgone ecosystem service benefits. Minimizing further damage from hydropower development requires considering diverse environmental impacts across the entire basin, as well as cooperation among Amazonian nations. Our findings offer a transferable model for the evaluation of hydropower expansion in transboundary basins.

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Although biodiversity loss adversely influences a variety of ecosystem functions, how declining wild food diversity affects nutrient supplies for people is poorly understood. Here, we analyze the impact of declining biodiversity on nutrients supplied by fish using detailed information from the Peruvian Amazon, where inland fisheries provide a critical source of nutrition for many of the region’s 800,000 people. We found that the impacts of biodiversity loss on nutrient supplies depended on compensation, trophic dynamics, and functional diversity. When small sedentary species compensated for declines in large migratory species, fatty acid supplies increased, while zinc and iron supplies decreased. In contrast, the probability of failing to maintain supplies or nutrient supply risk increased when species were nutritionally unique. Our results show that trait-based regulations and public health polices need to consider biodiversity’s vital role in sustaining nutritional benefits for over 2 billion people dependent on wild foods across the globe.

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Changes in biodiversity can severely affect ecosystem functioning, but the impacts of species loss on an ecosystem's ability to sustain multiple functions remain unclear. When considering individual functions, the impacts of biodiversity loss depend on correlations between species functional contributions and their extinction probabilities. When considering multiple functions, the impacts of biodiversity loss depend on correlations between species contributions to individual functions. However, how correlations between extinction probabilities and functional contributions determine the impact of biodiversity loss on multifunctionality (MF) is not well understood. Here, we use biodiversity loss simulations to examine the influence of correlations among multiple functions and extinction probabilities on the diversity–MF relationship. In contrast with random extinction, we find that the response of MF to biodiversity loss is influenced by the absence of positive correlations between species functional contributions, rather than by negative correlations. Communities with a high number of pairwise positive correlations in functional contributions achieve higher levels of MF, but are also less resilient to extinction. This work implies that understanding how species extinction probabilities correlate with their contribution to MF can help identify the degree to which MF will change with ongoing biodiversity loss and target conservation efforts to maximize MF resiliency.