Biotic differentiation in headwater creeks after the massive introduction of non-native freshwater aquarium fish in the Paraíba do Sul River basin, Brazil

This study evaluated fish beta diversity in six headwater creeks located in the area affected by the largest ornamental aquaculture center implemented in the Minas Gerais State, southeastern Brazil. We sampled fish assemblages in 2017 and 2018 to investigate changes in assemblage structure (species richness and beta diversity), comparing these data with the historic species pool. We recorded 60 fish species, of which 16 were native and 44 non-native with 19 translocated, and 25 exotic. The exotics Poecilia reticulata, Xiphophorus maculatus, X. variatus, Danio rerio, and Misgurnus anguillicaudatus were the most widely distributed in the headwater creeks. The Contamination Index showed that most creeks had high proportional contamination by exotic species (above 60%). Beta diversity increased from historical to contemporary periods in all creeks due to the introduction and differential colonization pressure of several non-native translocated and exotic species, indicating biotic differentiation. Temperature and number of ponds were the main preditors of change in beta diversity in the headwater creeks during the contemporary period. In summary, we observed that invaders have induced substantial changes to fish communities under influence of environmental filters. Our results support the hipothesis that aquaculture is a main driver of fish non-native fish introduction and native biodiversity loss in the Neotropics.

Oligocene divergence of frogmouth birds (Podargidae) across Wallace's Line

Wallace's Line demarcates the transition between the differentiated regional faunas of Asia and Australia. However, while patterns of biotic differentiation across these two continental landmasses and the intervening island groups (Wallacea) have been extensively studied, patterns of long-term dispersal and diversification across this region are less well understood. Frogmouths (Aves: Podargidae) are a relictual family of large nocturnal birds represented by three extant genera occurring, respectively, in Asia, ‘Sahul’ (Australia and New Guinea) and the Solomon Islands, thus spanning Wallace's Line. We used new mitochondrial genomes from each of the extant frogmouth genera to estimate the timeline of frogmouth evolution and dispersal across Wallace's Line. Our results suggest that the three genera diverged and dispersed during the mid-Cenozoic between approximately 30 and 40 Mya. These divergences are among the oldest inferred for any trans-Wallacean vertebrate lineage. In addition, our results reveal that the monotypic Solomons frogmouth ( Rigidipenna inexpectata ) is one of the most phylogenetically divergent endemic bird lineages in the southwest Pacific. We suggest that the contemporary distribution of exceptionally deep divergences among extant frogmouth lineages may be explained by colonization of, and subsequent long-term persistence on, island arcs in the southwest Pacific during the Oligocene. These island arcs may have provided a pathway for biotic dispersal out of both Asia and Australia that preceded the formation of extensive emergent landmasses in Wallacea by at least 10 million years.

Pattern and process of biotic homogenization in the New Pangaea

Human activities have reorganized the earth's biota resulting in spatially disparate locales becoming more or less similar in species composition over time through the processes of biotic homogenization and biotic differentiation, respectively. Despite mounting evidence suggesting that this process may be widespread in both aquatic and terrestrial systems, past studies have predominantly focused on single taxonomic groups at a single spatial scale. Furthermore, change in pairwise similarity is itself dependent on two distinct processes, spatial turnover in species composition and changes in gradients of species richness. Most past research has failed to disentangle the effect of these two mechanisms on homogenization patterns. Here, we use recent statistical advances and collate a global database of homogenization studies (20 studies, 50 datasets) to provide the first global investigation of the homogenization process across major faunal and floral groups and elucidate the relative role of changes in species richness and turnover. We found evidence of homogenization (change in similarity ranging from −0.02 to 0.09) across nearly all taxonomic groups, spatial extent and grain sizes. Partitioning of change in pairwise similarity shows that overall change in community similarity is driven by changes in species richness. Our results show that biotic homogenization is truly a global phenomenon and put into question many of the ecological mechanisms invoked in previous studies to explain patterns of homogenization.

Community Ecology of Stream Fishes: Concepts, Approaches, and Techniques

<em>Abstract</em>.—Widespread introduction of common species coupled with extirpation of endemic species can cause fish assemblages to lose much of their regional uniqueness. This process of biotic homogenization contrasts with biotic differentiation, whereby initially similar fish faunas diverge due to introductions of different species. The relative importance of homogenization and differentiation in altering fish faunas has been examined across the world. Synthesis of these studies indicates that homogenization of fish faunas has been widespread and that introductions, especially of sport fishes, have played a bigger role in altering fish faunas than extirpations. In the United States, pairs of states now average 15.4 more species in common than before European settlement. Additionally, the 89 pairs of states that formerly had no fish species in common now share an average of 25.2 species. While homogenization is prevalent at large spatial scales, differentiation of fish faunas is evident at intermediate spatial scales such as among watersheds within an ecoregion. This differentiation is largely the result of the idiosyncratic nature of fish introductions among individual lakes and streams. In general, translocated species (i.e., species that are native somewhere in the region but that have been moved to new locations) cause homogenization, whereas exotic species (species not native to the region) cause differentiation. Habitat and flow homogenization are major drivers of biotic homogenization because altered habitats create conditions that favor a few generalist species at the expense of more-specialized endemic species.

Growth and survival of white clover (Trifolium repens) transplanted into patches of different grass species

Previous studies on Trifolium repens L. showed differentiation with respect to neighbouring plant species and local environmental conditions. In this study, we conducted a series of reciprocal transplants among and within different pastures and among neighbouring grass species (Lolium perenne L., Dactylis glomerata L., and Holcus lanatus L.). While the presence of a grass neighbour decreased survival and growth of T. repens, no evidence of differentiation by T. repens to either local environmental conditions or to neighbouring grass species was found. We suggest that T. repens, in systems like our study pastures that have small, transient grass patches, may show inconsistent and ephemeral responses to the presence of neighbouring plants, whereas in other systems with larger grass patch size and a longer period of exposure to selection processes, T. repens show fine-scale biotic differentiation to neighbouring grass species. Keywords: population differentiation, white clover, selection, microevolution, transplantation.