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Species richness is the most commonly used metric to quantify biodiversity. However, examining dark diversity, the group of absent species which can potentially inhabit a site, can provide additional insights about how communities are assembled. In this study we aimed to understand how human impacts and environment affect the observed diversity, dark diversity, completeness (how large is the observed diversity compared to dark diversity) and species pool size (observed and dark diversity together) of vascular plants (i.e., trees, shrubs, herbs and lianas) in Caatinga. Along 144 0.4 ha plots for trees and 0.04 ha plots for shrubs, herbs, and lianas, we recorded 2148 stems from 232 native species. We show that larger, well-connected and wetter fragments present either more observed diversity or larger species pools of vascular plants, indicating that these fragments may act as biodiversity reservoirs in Caatinga. However, these drivers are usually plant life-form dependent, with some variables such as chronic anthropogenic disturbance, habitat amount, soil and temperature also playing secondary roles on observed and dark diversity of different life-forms. Overall, by including dark diversity in the analyses we were able to identify additional effects of human impacts and environment on vegetation change, which would not be possible to be captured by using species richness only. Finally, our results highlight the complexity of human-modified landscapes in dry forests and stress the importance of considering the whole species pool of plants and different growth life-forms when assessing the effects of disturbance and environment on Caatinga vegetation. [ABSTRACT FROM AUTHOR]

Habitat loss is an important factor in global biodiversity loss, but categorizing human-modified landscapes as fragments of natural or anthropogenic habitats may underestimate our impact on biodiversity since most natural fragments suffer from chronic anthropogenic disturbances. Here, we tested the synergistic effect between habitat loss and chronic anthropogenic disturbances on ant communities of the Caatinga, a seasonally dry tropical forest in South America. From online sources and published material, we built a data-set containing information on habitat loss and chronic anthropogenic disturbance index, as well as its vectors (i.e., human population density, infrastructure, logging, fire, and grazing), for 23 Caatinga localities containing information on ant community composition. Generalized linear models demonstrated that habitat loss interacts with chronic anthropogenic disturbance to determine total ant richness and the richness of habitat specialist ants. Furthermore, habitat loss interacts synergistically with several vectors of chronic anthropogenic disturbances to determine ant richness. In general, the effect of habitat loss is exacerbated by human population density, infrastructures, logging, and grazing. The proportion of habitat specialists in the communities did not respond to habitat loss or chronic anthropogenic vectors, suggesting that both ant groups were equally affected by habitat alterations. Although habitat amount is an important predictor of the integrity of the local biodiversity, it tends to underestimate our impact on biological communities. The incorporation of estimates of habitat quality can help us build better models to predict our impact on Earth. [ABSTRACT FROM AUTHOR]

Although chronic anthropogenic disturbance (CAD) represents a significant threat to the integrity of tropical biotas, few efforts have been made to understand its impacts. We address the effects of CAD on plant and ant communities in the Caatinga, a seasonally dry tropical forest in northeast Brazil. Both taxa were recorded across 25 0.1-ha plots within a 220-km landscape dominated by old-growth vegetation exposed to human activities. CAD was measured indirectly via a disturbance index, which was calculated from proxies of human disturbance such as plot distance to roads and villages, and density of people and livestock. Plant and ant abundance was not correlated to the CAD index. However, CAD had negative, positive or neutral effects on species diversity, depending upon diversity measure, taxa and soil type; e.g. plants were more negatively affected than ants. Furthermore, several plant and ant species exhibited higher abundance in the most disturbed vegetation patches while some exhibited lower abundance. Species-level responses resulted in taxonomic responses at the community level and increments in cross-plot species similarity as CAD increased. Our results indicate that: (1) CAD affects several community-level attributes, but with differing intensities; (2) community-level effects can be either positive or negative, and effects are soil dependent; (3) plants are more negatively affected than ants; (4) some species benefit, while others are negatively affected by CAD; and (5) by affecting the abundance and occurrence of particular species, CAD causes biotic homogenization towards the higher end of the disturbance gradient. [ABSTRACT FROM AUTHOR]

Humans are promoting drastic changes in biological communities that result in 'winner-loser' species replacements across multiple spatial scales. In tropical regions, such replacements can be particularly driven by deforestation, especially in landscapes devoted to free-ranging livestock production in which mixing native and exotic species can create species-poor and homogenized communities. We tested this hypothesis assessing medium- and large-bodied non-volant mammals in four 16-km2 landscapes with varying deforestation levels (5%, 30%, 70%, and 95% forest cover), where exotic mammals (e.g., cows and goats) have free access to the remaining Caatinga dry forest. Using camera traps, we obtained 2808 independent records of 17 species, most of them (2054 records, 73%) corresponding to seven exotic species. Native Cerdocyon thous (crab-eating fox) and exotic Capra hircus (goat) accounted for almost half of the records and 60–80% of the records in the two most deforested landscapes. Alpha diversity did not differ significantly among landscapes, but the two more forested landscapes tended to have more native species than exotic ones. Beta diversity patterns among and within landscapes were relatively low regardless of species abundance, indicating biotic homogenization at multiple spatial scales. We conclude that a novel mammal community full of exotic mammals and a few generalist natives has been established in the study region. To promote environmental-friendly livestock farming in the largest tropical dry forest of South America, we should avoid deforestation, especially in sites that concentrate native species, segregate lands for livestock and conservation, and boost inspection against illegal hunting. [ABSTRACT FROM AUTHOR]

Meeting Brazil's ambitious national commitments on both climate change mitigation and biodiversity conservation depends on securing its reserves of forest carbon and biodiversity. Brazil's 'Forest Code' is a key tool to reconcile environmental preservation and agricultural production; it limits deforestation and requires forest restoration in illegally deforested areas. However, not all provisions of the law's 2012 revision have yet been implemented and some are facing new challenges. Using modelled land use change projections for the whole of the country, we show that full implementation and enforcement of the law has the potential to contribute to conserving biodiversity. Biodiversity outcomes will be especially positive if (i) deforested areas are restored in ways that support recolonization by native species and (ii) additional measures are implemented to protect native vegetation in areas like Caatinga dry forests and Cerrado savannas, which may experience added pressure displaced from other regions by Forest Code implementation. [ABSTRACT FROM AUTHOR]

In the neotropical region, seasonally dry tropical forests (SDTF) are commonly associated with scatterly distributed limestone outcrops, known for harbouring high numbers of endemic species and genera. In the context of lacking knowledge on fine-scale vegetation and environmental heterogeneity of these geoecosystems and having a limestone outcrop in eastern Brazil as a case study, we address the question: how important are limestone outcrops for SDTF tree community composition, structure, function and evolution? We distinguished five habitats related to position and distance to the outcrop, and within each of 25 sampled plots (five per habitat), we identified and measured the diameter of all living tree individuals and collected soil samples for chemical and textural analyses. We investigated taxonomic and phylogenetic substitution across the habitats and fitted linear models to test the effects of habitat type, soil fertility and texture on taxonomic/structural, functional and phylogenetic parameters. We found striking taxonomic and phylogenetic differentiation among the habitats, especially related to recent diversification, with soil fertility and texture largely accounting for variations in all analysed parameters. Given the predominant roles of vicariance and in situ diversification believed to have given rise to the current patterns of endemism and diversity of eastern Brazil SDTF, we argue that the conditions presented by limestone outcrops, including aridity and high fertility, may have favoured the persistence of SDTF lineages during the Quaternary environmental changes, highlighting their role as litho-refugia. In order to complete this biogeographic puzzle, we encourage other fine-scale assessments of outcrop-associated SDTF from the phylogenetic viewpoint. [ABSTRACT FROM AUTHOR]

Intensive deforestation is reducing dry tropical forest areas worldwide and increasing its fragmentation. Forest remnants can be the basis for the future recovery of this forest type if appropriate management practices are applied. This requires a better knowledge of their conservation status and the assessment of their perceived value by land users. In this study we compare the structure, species richness and diversity of different types of tropical dry forest remnants in Nicaragua and we assess their conservation status based on a new index: Social simplified Importance Value Index (SsIVI). This index summarizes both ecological indicators and the perception by local stakeholders of the conservation status of the tree species present. Results show that gallery and hillslope forest remnants have higher species richness and diversity than isolated vestigial patches. In all remnants, species richness and diversity is higher in the tree layer than in the regeneration layer. No differences are observed in valorisation among different types of remnants either for the tree layer or for the regeneration layer. In the hillslope forests, where several degrees of disturbance are present, the valorisation decreases with increasing degradation. Results of species composition and forest structure indicate a strong degradation of dry tropical forest remnants in Nicaragua. However, the similar social valorisation of the three types of remnants suggests that they face similar threats but also similar opportunities to be preserved. A decrease in valorisation with increasing degradation warns about the potential loss of the most degraded areas, unless forest restoration is applied. [ABSTRACT FROM AUTHOR]