Tropical and temperate differences in the trophic structure and aquatic prey use of riparian predators.

The influence of aquatic resource-inputs on terrestrial communities is poorly understood, particularly in the tropics. We used stable isotope analysis of carbon and nitrogen to trace aquatic prey use and quantify the impact on trophic structure in 240 riparian arthropod communities in tropical and temperate forests. Riparian predators consumed more aquatic prey and were more trophically diverse in the tropics than temperate regions, indicating tropical riparian communities are both more reliant on and impacted by aquatic resources than temperate communities. This suggests they are more vulnerable to disruption of aquatic-terrestrial linkages. Although aquatic resource use declined strongly with distance from water, we observed no correlated change in trophic structure, suggesting trophic flexibility to changing resource availability within riparian predator communities in both tropical and temperate regions. Our findings highlight the importance of aquatic resources for riparian communities, especially in the tropics, but suggest distance from water is less important than resource diversity in maintaining terrestrial trophic structure.

Effects of warming on the structure of aquatic communities in tropical bromeliad microecosystems.

Freshwaters are among the most vulnerable ecosystems to climate warming, with projected temperature increases over the coming decades leading to significant losses of aquatic biodiversity. Experimental studies that directly warm entire natural ecosystems in the tropics are needed, for understanding the disturbances on aquatic communities. Therefore, we conducted an experiment to test the impacts of predicted future warming on density, alpha diversity, and beta diversity of freshwater aquatic communities, inhabiting natural microecosystems-Neotropical tank bromeliads. Aquatic communities within the tanks bromeliads were experimentally exposed to warming, with temperatures ranging from 23.58 to 31.72°C. Linear regression analysis was used to test the impacts of warming. Next, distance-based redundancy analysis was performed to assess how warming might alter total beta diversity and its components. This experiment was conducted across a gradient of habitat size (bromeliad water volume) and availability of detrital basal resources. A combination of the highest detritus biomass and higher experimental temperatures resulted in the greatest density of flagellates. However, the density of flagellates declined in bromeliads with higher water volume and lower detritus biomass. Moreover, the combination of the highest water volume and high temperature reduced density of copepods. Finally, warming changed microfauna species composition, mostly through species substitution (ß repl component of total beta-diversity). These findings indicate that warming strongly structures freshwater communities by reducing or increasing densities of different aquatic communities groups. It also enhances beta-diversity, and many of these effects are modulated by habitat size or detrital resources.

Pervasive decline of subtropical aquatic insects over 20 years driven by water transparency, non-native fish and stoichiometric imbalance.

Insect abundance and diversity are declining worldwide. Although recent research found freshwater insect populations to be increasing in some regions, there is a critical lack of data from tropical and subtropical regions. Here, we examine a 20-year monitoring dataset of freshwater insects from a subtropical floodplain comprising a diverse suite of rivers, shallow lakes, channels and backwaters. We found a pervasive decline in abundance of all major insect orders (Odonata, Ephemeroptera, Trichoptera, Megaloptera, Coleoptera, Hemiptera and Diptera) and families, regardless of their functional role or body size. Similarly, Chironomidae species richness decreased over the same time period. The main drivers of this pervasive insect decline were increased concurrent invasions of non-native insectivorous fish, water transparency and changes to water stoichiometry (i.e. N : P ratios) over time. All these drivers represent human impacts caused by reservoir construction. This work sheds light on the importance of long-term studies for a deeper understanding of human-induced impacts on aquatic insects. We highlight that extended anthropogenic impact monitoring and mitigation actions are pivotal in maintaining freshwater ecosystem integrity.

Warming of aquatic ecosystems disrupts aquatic-terrestrial linkages in the tropics.

Aquatic ecosystems are tightly linked to terrestrial ecosystems by exchanges of resources, which influence species interactions, community dynamics and functioning in both ecosystem types. However, our understanding of how this coupling responds to climate warming is restricted to temperate, boreal and arctic regions, with limited knowledge from tropical ecosystems. We investigated how warming aquatic ecosystems impact cross-ecosystem exchanges in the tropics, through the export of aquatic resources into the terrestrial environment and the breakdown of terrestrial resources within the aquatic environment. We experimentally heated 50 naturally assembled aquatic communities, contained within different-sized tank-bromeliads, to a 23.5-32°C gradient of mean water temperatures. The biomass, abundance and richness of aquatic insects emerging into the terrestrial environment all declined with rising temperatures over a 45-day experiment. Structural equation and linear mixed effects modelling suggested that these impacts were driven by deleterious effects of warming on insect development and survival, rather than being mediated by aquatic predation, nutrient availability or reduced body size. Decomposition was primarily driven by microbial activity. However, total decomposition by both microbes and macroinvertebrates increased with temperature in all but the largest ecosystems, where it decreased. Thus, warming decoupled aquatic and terrestrial ecosystems, by reducing the flux of aquatic resources to terrestrial ecosystems but variably enhancing or reducing terrestrial resource breakdown in aquatic ecosystems. In contrast with increased emergence observed in warmed temperate ecosystems, future climate change is likely to reduce connectivity between tropical terrestrial and aquatic habitats, potentially impacting consumers in both ecosystem types. As tropical ectotherms live closer to their thermal tolerance limits compared to temperate species, warming can disrupt cross-ecosystem dynamics in an interconnected tropical landscape and should be considered when investigating ecosystem-level consequences of climate change.

Os ecossistemas aquáticos estão intimamente ligados aos ecossistemas terrestres por meio das trocas de recursos, que influenciam as interações entre as espécies, a dinâmica da comunidade e o funcionamento de ambos os tipos de ecossistemas. No entanto, nosso entendimento de como esse acoplamento responde ao aquecimento do clima é restrito às regiões temperadas, boreais e árticas, com conhecimento limitado para os ecossistemas tropicais. Investigamos como o aquecimento dos ecossistemas aquáticos impacta as trocas entre os ecossistemas nos trópicos, por meio da exportação de recursos aquáticos para o ambiente terrestre e da decomposição dos detritos de origem terrestre no ambiente aquático. Nós aquecemos experimentalmente 50 comunidades aquáticas que habitam tanques de bromélias de diferentes tamanhos, submetidas a um gradiente de temperatura média da água variando de 23,5 a 32°C. Em um experimento de 45 dias, a biomassa, abundância e riqueza de insetos aquáticos emergindo para o ambiente terrestre diminuíram com o aumento da temperatura. Modelos lineares mistos e de equações estruturais sugerem que esses impactos foram causados por efeitos deletérios do aquecimento no desenvolvimento e sobrevivência dos insetos, ao invés de serem mediados por predadores aquáticos, disponibilidade de nutrientes ou tamanho corporal reduzido. A decomposição foi determinada principalmente pela atividade microbiana. A decomposição total por micro-organismos e macro invertebrados aumentou com a temperatura, exceto em ecossistemas maiores. Assim, o aquecimento dissociou os ecossistemas aquáticos e terrestres, reduzindo o fluxo de recursos aquáticos para os ecossistemas terrestres, mas aumentando ou reduzindo de forma variável a decomposição dos recursos terrestres nos ecossistemas aquáticos. Em contraste com o aumento da emergência observada em ecossistemas temperados aquecidos, as mudanças climáticas futuras provavelmente reduzirão a conectividade entre os habitats terrestres e aquáticos tropicais, impactando potencialmente os consumidores em ambos os tipos de ecossistemas. Como organismos ectotérmicos tropicais vivem mais perto dos seus limites de tolerância térmica em comparação com espécies temperadas, o aquecimento pode comprometer a dinâmica entre os ecossistemas em uma paisagem tropical interconectada e deve ser considerado ao investigar as consequências das mudanças climáticas no nível do ecossistema.

Long-term survey of sea turtles (Caretta caretta) reveals correlations between parasite infection, feeding ecology, reproductive success and population dynamics.

Long-term monitoring of host-parasite interactions is important for understanding the consequences of infection on host fitness and population dynamics. In an eight-year survey of the loggerhead sea turtle (Caretta caretta) population nesting in Cabo Verde, we determined the spatiotemporal variation of Ozobranchus margoi, a sanguivorous leech best known as a vector for sea turtle fibropapilloma virus. We quantified O. margoi association with turtles' δ15N and δ13C stable isotopes to identify where infection occurs. We then measured the influence of infection on reproduction and offspring fitness. We found that parasite prevalence has increased from 10% of the population in 2010, to 33% in 2017. Stable isotope analysis of host skin samples suggests transmission occurs within the host's feeding grounds. Interestingly, we found a significant interaction between individual size and infection on the reproductive success of turtles. Specifically, small, infected females produced fewer offspring of poorer condition, while in contrast, large, infected turtles produced greater clutch sizes and larger offspring. We interpret this interaction as evidence, upon infection, for a size-dependent shift in reproductive strategy from bet hedging to terminal investment, altering population dynamics. This link between infection and reproduction underscores the importance of using long-term monitoring to quantify the impact of disease dynamics over time.