Beta diversity of stream insects differs between boreal and subtropical regions, but land use does not generally cause biotic homogenization

Previous studies have found mixed results regarding the relationship between beta diversity and latitude. In addition, by influencing local environmental heterogeneity, land use may modify spatial taxonomic and functional variability among communities causing biotic differentiation or homogenization. We tested 1) whether taxonomic and functional beta diversities among streams within watersheds differ between subtropical and boreal regions and 2) whether land use is related to taxonomic and functional beta diversities in both regions. We sampled aquatic insects in 100 subtropical (Brazil) and 100 boreal (Finland) streams across a wide gradient of land use, including agriculture and exotic planted, secondary, and native forests. We calculated beta diversity at the watershed scale (among 5 streams in each watershed). We found higher taxonomic beta diversity among subtropical than among boreal streams, whereas functional beta diversity was similar between the 2 regions. Total land use was positively correlated with taxonomic and functional beta diversity among subtropical streams, while local environmental heterogeneity was positively correlated with beta diversity among boreal streams. We suggest that different types and intensities of land use may increase among-stream heterogeneity, promoting distinct insect assemblage compositions among streams. Our findings also suggest that beta diversity patterns and their underlying determinants are highly context dependent

Influência da heterogeneidade ambiental sobre os atributos da comunidade de Chironomidae em lagoas de inundação neotropicais

A estrutura do ambiente é um importante fator que influencia a distribuição das comunidades. Neste sentido, ambientes fisicamente mais complexos sustentam maior riqueza de espécies que aqueles mais simples. Este estudo teve por objetivo avaliar a influência da heterogeneidade ambiental sobre os atributos da comunidade de Chironomidae, determinando a distribuição espacial do grupo em diferentes lagoas da planície de inundação do alto rio Paraná. As coletas foram realizadas trimestralmente de março a dezembro de 2011, em seis ambientes (três lagoas com conexão e três lagoas sem conexão ao rio principal). A heterogeneidade das lagoas foi determinada pelo Escore Ambiental, o qual foi calculado através da soma das características físicas, químicas e biológicas das lagoas. As correlações entre o Escore Ambiental das lagoas com a riqueza, densidade e a diversidade de larvas de Chironomidae foram significativas. Tais resultados sugerem que as lagoas com maior Escore Ambiental ou maior heterogeneidade são mais propícias à suportar um número mais elevado de indivíduos e de táxons

The invasive aquatic macrophyte Hydrilla verticillata facilitates the establishment of the invasive mussel Limnoperna fortunei in Neotropical reservoirs

<p>The effects of introduced species on native species have been widely studied, however, invader-invader interactions are still poorly explored. Two non-native invasive species, the bivalve <em>Limnoperna</em> <em>fortunei</em> and the submersed macrophyte <em>Hydrilla</em> <em>verticillata</em>, have infested many aquatic ecosystems worldwide, and they are rapidly becoming nuisances in several water bodies in Brazil. We tested the hypothesis that <em>H</em>. <em>verticillata</em> facilitates the establishment of <em>L.</em> <em>fortunei</em> more than do native macrophytes. We surveyed mussels attached to two native macrophytes and to this invasive macrophyte in three Brazilian reservoirs and compared the length, density and biomass of the attached mussels relative to the host macrophyte species. All of the values of these attributes in <em>L. fortunei</em> were higher in the mussels attached to <em>H. verticillata</em> than in those attached to the native macrophytes. These results supported our initial hypothesis because the settlement of <em>L. fortunei</em> appeared to be facilitated by the invasive macrophyte, allowing higher abundances of the mussels as well as the more effective establishment of the mussel population. Various mechanisms could interact to facilitate the superior performance of <em>L.</em> <em>fortunei</em> in the invasive plant. <em>H. verticillata</em> is more flexible and withstands more mussels without breaking. Furthermore, this plant has different attached algae, which may be more beneficial for mussels. Thus, as a response to the facilitation suggested by our work, the mussel has greater opportunities to succeed in habitats colonised by the non-native <em>H. verticillata</em>. Although we have not evaluated the effects of this facilitation on aquatic communities or the ecosystem, our results could represent the first step of an invasional meltdown.</p

Community size can affect the signals of ecological drift and niche selection on biodiversity

Ecological drift can override the effects of deterministic niche selection on small populations and drive the assembly of some ecological communities. We tested this hypothesis with a unique data set sampled identically in 200 streams in two regions (tropical Brazil and boreal Finland) that differ in macroinvertebrate community size by fivefold. Null models allowed us to estimate the magnitude to which beta-diversity deviates from the expectation under a random assembly process while taking differences in richness and relative abundance into account, i.e., beta-deviation. We found that both abundance- and incidence-based beta-diversity was negatively related to community size only in Brazil. Also, beta-diversity of small tropical communities was closer to stochastic expectations compared with beta-diversity of large communities. We suggest that ecological drift may drive variation in some small communities by changing the expected outcome of niche selection, increasing the chances of species with low abundance and narrow distribution to occur in some communities. Habitat destruction, overexploitation, pollution, and reductions in connectivity have been reducing the size of biological communities. These environmental pressures might make smaller communities more vulnerable to novel conditions and render community dynamics more unpredictable. Incorporation of community size into ecological models should provide conceptual and applied insights into a better understanding of the processes driving biodiversity.peerReviewe

Upstream refugia and dispersal ability may override benthic-community responses to high-Andean streams deforestation

Deforestation is a major driver of biodiversity loss in the Tropical region, but the role of upstream refugia and dispersal ability on the community response to this disturbance is unknown. We assessed the relevance of undisturbed upstream patches (“refugia”) on the responses of benthic communities to forest cover loss. We selected four Andean rivers with a well-protected forest in their upstream section and different degree of forest cover loss downstream and evaluated the dissimilarity patterns of three benthic communities (diatoms, Chironomidae, and the assemblage of Ephemeroptera, Plecoptera and Trichoptera—‘EPT’) along their water courses. We evaluated the dissimilarity by using Euclidean (environment), Sørensen (incidence data) and Morisita–Horn (abundance data) pairwise distances. We found that diatom beta-diversity, as organisms with passive but higher dispersal ability, significantly tracked the environmental changes caused by forest loss. However, insect communities, whose a priori are active dispersers and can track for suitable conditions, were weakly affected by deforestation. These results provide evidences that the existence of well-preserved upstream reaches along patched corridors may allow non-tolerant species to remain extant throughout dispersal-driven feedbacks. This being the case in the Andean streams, effects of deforestation on benthic communities were small, and not uniform. Our results reinforce the strategy of preserving upstream sections in order to achieve successful restoration or rehabilitation goals

Neotropical freshwater fisheries : A dataset of occurrence and abundance of freshwater fishes in the Neotropics

The Neotropical region hosts 4225 freshwater fish species, ranking first among the world's most diverse regions for freshwater fishes. Our NEOTROPICAL FRESHWATER FISHES data set is the first to produce a large-scale Neotropical freshwater fish inventory, covering the entire Neotropical region from Mexico and the Caribbean in the north to the southern limits in Argentina, Paraguay, Chile, and Uruguay. We compiled 185,787 distribution records, with unique georeferenced coordinates, for the 4225 species, represented by occurrence and abundance data. The number of species for the most numerous orders are as follows: Characiformes (1289), Siluriformes (1384), Cichliformes (354), Cyprinodontiformes (245), and Gymnotiformes (135). The most recorded species was the characid Astyanax fasciatus (4696 records). We registered 116,802 distribution records for native species, compared to 1802 distribution records for nonnative species. The main aim of the NEOTROPICAL FRESHWATER FISHES data set was to make these occurrence and abundance data accessible for international researchers to develop ecological and macroecological studies, from local to regional scales, with focal fish species, families, or orders. We anticipate that the NEOTROPICAL FRESHWATER FISHES data set will be valuable for studies on a wide range of ecological processes, such as trophic cascades, fishery pressure, the effects of habitat loss and fragmentation, and the impacts of species invasion and climate change. There are no copyright restrictions on the data, and please cite this data paper when using the data in publications