1. River damming and other anthropogenic disturbances of natural habitats are among the main drivers of species loss through a range of direct and indirect effects. While the effects of river damming on aquatic species are relatively well studied, particularly with regard to their impacts on diadromous species and stenotopic riverine specialists, there is a paucity of studies quantifying the effects of dam construction on whole communities. 2. We conducted a global meta-analysis focussed on fish communities, comparing species richness, abundance and proportion of alien species between dammed and undammed rivers. Both longitudinal and cross-sectional studies were examined. 3. We found that construction of dams did not have a noticeable effect on fish richness and abundance, but the increase in proportion of alien species was significant (mean effect size of 0.62). 4. Our findings suggest that the conversion of lotic waterbodies into lentic habitats result in the extirpation of species unable to withstand a drastic change in environmental conditions, but the loss is compensated by colonising lacustrine or eurytopic species taking advantage of reduced competition and the availability of new niches specific to lentic habitats. However, when eurytopic natives are absent from waterbodies connected to the newly constructed reservoirs, vacant niches are instead exploited by alien species, resulting in impoverishment of native species richness although overall species richness may be maintained.

Flow of terrestrial carbon though aquatic ecosystems (allochthony) is an important but underestimated component of the global carbon cycle. A lack of clear consensus about the importance of allochthonous (terrestrial) organic carbon is sometimes attributed to uncertainties associated with conventional ‘bulk’ isotope data, the most widely used ecological tracer. Amino acid‐specific isotope analysis is an emerging research method promising to address existing limitations of bulk C and N isotope analyses. We tested the efficacy of amino acid δ13C data as a generalizable measure of allochthony by analysing an aggregated dataset (n = 168) of primary and secondary data of carbon sources from disparate geographical locations across the globe. We found the δ13C fingerprints amino acids to be consistently distinct between allochthonous (terrestrial) and autochthonous (aquatic) carbon sources. We also found that our approach is most effective when we use only essential amino acid tracers (i.e. isoleucine, leucine, phenylalanine, threonine and valine). Predictive trends in δ13C fingerprints appear to be largely compatible across studies and/or laboratories. As a case study, we used this approach to quantify the contribution of terrestrial carbon to an endemic cavefish, Cryptotora thamicola, and found that its biomass was comprised largely of autochthonous carbon (~75%).

Compound‐specific isotope analysis of amino acids (CSIA‐AA) is a promising nascent technique that alleviates many shortcomings of conventional bulk‐tissue stable isotope analysis (“bulk SIA”) in ecological studies involving the tracing/reconstruction of carbon and nitrogen pathways. While CSIA‐AA has been increasingly applied to preserved tissue samples (e.g., material in natural history collections), the effects of sample preservation on amino acid δ13C and δ15N profiles are poorly understood. It is therefore unclear if mathematical correction factors are necessary for interpreting isotopic profiles of preserved samples. In this study, we investigated effects of ethanol preservation and formalin fixation on amino acid δ13C and δ15N profiles. We also assess how these effects translate to two ecological applications of CSIA‐AA: quantification of organic carbon sources, and estimation of trophic positions. Results from an 8‐week controlled experiment on freshwater fish tissue show negligible preservation effects on most amino acid δ15N profiles, and results are similar for δ13C profiles of essential amino acids. Findings from mixing models using essential amino acid δ13C profiles similarly show that preserved samples can yield robust estimates of carbon source contributions. We also empirically demonstrate, for the first time, the use of amino acid δ13C profiles to enhance δ15N‐based estimates of trophic position in food webs with multiple producers, and show that these estimates are not compromised by preservation effects. Overall, our findings support the view that amino acid δ13C and δ15N profiles from ethanol‐ and formalin‐treated CSIA‐AA samples can be directly used for addressing ecological questions.

This study asked whether reductive traits in cave organisms evolve at a slower pace (suggesting neutral evolution under relaxed selection) than constructive changes, which are likely to evolve under directional selection. We investigated 11 subterranean and seven surface populations of Sundathelphusa freshwater crabs on Bohol Island, Philippines, and examined constructive traits associated with improved food finding in darkness (increased leg and setae length) and reductive traits (reduced cornea size and eyestalk length). All changes occurred rapidly, given that the age of the most recent common ancestor was estimated to be 722-271 ka based on three mitochondrial markers. In order to quantify the speed of character change, we correlated the degree of morphological change with genetic distances between surface and subterranean individuals. The temporal pattern of character change following the transition to subterranean life was indistinguishable for constructive and reductive traits, characterized by an immediate onset and rapid evolutionary change. We propose that the evolution of these reductive traits-just like constructive traits-is most likely driven by strong directional selection.

The wildlife trade is a major cause of species loss and a pathway for disease transmission. Socioeconomic drivers of the wildlife trade are influential at the local scale yet rarely accounted for in multinational agreements aimed at curtailing international trade in threatened species. In recent decades (1998–2018), approximately 421,000,000 threatened (i.e., CITES-listed) wild animals were traded between 226 nations/territories. The global trade network was more highly connected under conditions of greater international wealth inequality, when rich importers may have a larger economic advantage over poorer exporting nations/territories. Bilateral trade was driven primarily by socioeconomic factors at the supply end, with wealthier exporters likely to supply more animals to the global market. Our findings suggest that international policies for reducing the global wildlife trade should address inequalities between signatory states, possibly using incentive/compensation-driven programs modeled after other transnational environmental initiatives (e.g., REDD+).

Studies of ecosystem functions are gaining traction in the scientific community along with a growing consensus that losses in ecosystem functions have widespread consequences. Food webs, which are networks comprising all trophic interactions (represented by links) between taxa present in a community (represented by nodes), are important aspects of ecosystem functioning, yet a clear understanding of the factors and mechanisms influencing their assembly and structure is lacking. In our study, we addressed this fundamental question by investigating the respective roles of (1) environmental filtering and (2) biotic filtering, in governing food web structure. We did this by assessing the relationship between the network structure of five high‐resolution empirical tropical food webs and associated environmental and biotic covariates. Our data suggest that only environmental filtering is important in shaping food webs. Further, we found that the underlying ecological mechanism is a function of bottom‐up influences comprising resource levels, and to a lesser degree, resource type (i.e., terrestrial organic matter) available. Specifically, our data suggest high‐nutrient environments favor greater food web complexity. In the general context of community assembly, our findings add to existing knowledge of the process by demonstrating that environmental conditions previously shown to influence species assemblages can also drive trends in prevailing species interactions.

Macrophytes are widely recognized for improving water quality and stabilizing the desirable clear‐water state in lakes. The positive effects of macrophytes on water quality have been noted to be weaker in the (sub)tropics compared to those of temperate regions. We conducted a global meta‐analysis using 47 studies that met our set criteria to assess the overall effects of macrophytes on water quality (measured by phytoplankton chlorophyll a concentration, total nitrogen concentration, total phosphorus concentration, Secchi depth and the trophic state index) and to investigate how these effects correlate with latitude using meta‐regressions. We also examined if the effects of macrophytes on lake‐water quality differ with growth form and study design in (sub)tropical and temperate areas by grouping the data and then comparing the effect sizes. We found that macrophytes significantly reduced phytoplankton chlorophyll a concentration, total nitrogen concentration, total phosphorus concentration, as well as the trophic state index, but they did not have a significant overall effect on Secchi depth. The effects of macrophytes on reducing phytoplankton chlorophyll a concentration, total nitrogen concentration and the trophic state index did not differ with latitude. However, the reduction of total phosphorus concentration was greater at lower latitudes. We showed that at lower latitudes, the positive effects of macrophytes on water quality are similar to or greater than those at higher latitudes, thus challenging the prevailing paradigm of macrophytes being less effective at enhancing lake‐water quality in the (sub)tropics. Furthermore, our data showed that the macrophyte effects vary by growth forms, and the growth forms that positively affect water quality differ between the (sub)tropical and temperate areas. We showed a lack of significant macrophyte effects in surveys within and outside macrophyte stands, suggesting difference in the sensitivities of study designs or possibly weaker effects of macrophytes in lakes compared to experimental settings.

In Southeast Asia, biodiversity-rich forests are being extensively logged and converted to oil palm monocultures. Although the impacts of these changes on biodiversity are largely well documented, we know little about how these large-scale impacts affect freshwater trophic ecology. We used stable isotope analyses (SIA) to determine the impacts of land-use changes on the relative contribution of allochthonous and autochthonous basal resources in 19 stream food webs. We also applied compound-specific SIA and bulk-SIA to determine the trophic position of fish apex predators and meso-predators (invertivores and omnivores). There was no difference in the contribution of autochthonous resources in either consumer group (70-82%) among streams with different land-use type. There was no change in trophic position for meso-predators, but trophic position decreased significantly for apex predators in oil palm plantation streams compared to forest streams. This change in maximum food chain length was due to turnover in identity of the apex predator among land-use types. Disruption of aquatic trophic ecology, through reduction in food chain length and shift in basal resources, may cause significant changes in biodiversity as well as ecosystem functions and services. Understanding this change can help develop more focused priorities for mediating the negative impacts of human activities on freshwater ecosystems.