Browsing by Subject "ABUNDANCE"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
Item Open Access A novel approach to assess livestock management effects on biodiversity of drylands(Ecological Indicators, 2015-01-01) Chillo, V; Ojeda, RA; Anand, M; Reynolds, JFIn drylands livestock grazing is the main production activity, but overgrazing due to mismanagement is a major cause of biodiversity loss. Continuous grazing around water sources generates a radial gradient of grazing intensity called the piosphere. The ecological sustainability of this system is questionable and alternative management needs to be evaluated. We apply simple indicators of species response to grazing gradients, and we propose a novel methodological approach to compare community response to grazing gradients (double reciprocal analysis). We assessed degradation gradients of biodiversity under different management strategies in semiarid rangelands of the Monte desert (Argentina) by analyzing changes in vegetation, ants and small mammal richness and diversity, and variation due to seasonality. At the species level, we determined the trend in abundance of each species along the gradient, and the potential cross-taxa surrogacy. At the community level, the new methodological consists of assessing the magnitude of biodiversity degradation along different piospheres by comparing the slopes of linear functions obtained by the double reciprocal analysis. We found that most species showed a decreasing trend along the gradient under continuous grazing; while under rotational grazing fewer species showed a decreasing trend, and a neutral trend (no change in the abundance along the gradient of grazing intensity) was the most common. We found that vegetation cannot be used as a surrogacy taxon of animal response. Moreover, weak cross-taxa surrogacy was found only for animal assemblages during the wet season. The double reciprocal analysis allowed for comparison of multi-taxa response under different seasons and management types. By its application, we found that constrains in precipitation interacted with disturbance by increasing the negative effect of grazing on vegetation, but not on animal assemblages. Continuous grazing causes biodiversity loss in all situations. Rotational grazing prevents the occurrence of vegetation degradation and maintains higher levels of animal diversity, acting as an opportunity for biodiversity conservation under current scenarios of land use extensification. Our approach highlights the importance of considering multi-taxa and intrinsic variability in the analysis, and should be of value to managers concerned with biodiversity conservation.Item Open Access Defaunation of large mammals alters understory vegetation and functional importance of invertebrates in an Afrotropical forest(Biological Conservation, 2020-01-01) Lamperty, Therese; Zhu, Kai; Poulsen, John R; Dunham, Amy EHunting has reduced or eliminated large-bodied vertebrates in many areas across the tropics, contributing to the global process of defaunation. Elucidating the ecological consequences of hunting has important implications for managing ecosystems and for our understanding of community and ecosystem ecology. We present data collected through a combination of comparative and experimental approaches to assess how faunally-intact and heavily-hunted forests in Gabon differ in understory vegetation structure, macroinvertebrate fauna, ecological processes, and the relative importance of different taxa driving those processes. Our results show that hunted sites had denser understory vegetation and hosted approximately 170 times fewer termites compared to faunally-intact sites. While web-building spiders were positively associated with understory vegetation density, this effect did not translate to significantly higher abundances in heavily-hunted forests. Additionally, the overall rates of decomposition, insectivory, and seed predation/removal on the forest floor appeared robust to both defaunation and the associated increases in understory vegetation density. However, our exclosure experiments revealed that the contribution of invertebrates to decomposition was approximately 25% lower in hunted sites compared to faunally-intact sites. Results suggest potential resilience in this complex ecosystem such that microbial or other taxa not measured in this study may compensate for the reduced functional contribution of invertebrates to decomposition. However, while our results illustrate potential resilience, they also indicate that indirect effects following defaunation, such as increases in the density of understory vegetation, may alter invertebrate communities on the forest floor, with potential consequences for the mechanisms, and therefore the dynamics, driving critical ecosystem processes.Item Open Access Zostera marina meadows from the Gulf of California: conservation status(Biodiversity and Conservation, 2016-02-01) Lopez-Calderon, Jorge M; Riosmena-Rodríguez, Rafael; Torre, Jorge; Meling, Alf; Basurto, Xavier© 2016, Springer Science+Business Media Dordrecht. Eelgrass (Zostera marina) population estimates show a decreasing trend worldwide in the second half of the twentieth century. Mexico lacks long-term time series to determine trends for major eelgrass populations and has made no conservation efforts. Therefore, we present the first report on the historic presence of this annual coastal ecosystem in two wetlands of the Gulf of California (GC), the Infiernillo Channel (CIF, largest Z. marina population inside GC) and Concepcion Bay (BCP, the only eelgrass population along GC’s west coast), combining field surveys (1999–2010), aerial photography (2000–2010), satellite imagery (1972–2005), and published reports (1994–2007). Three parameters were used as indicators of conservation status: shoot density, seed banks, and aerial coverage. Average shoot density in the CIF (741 shoots m−2) was 3.8 times higher than in BCP (194 shoots m−2), and average seed bank density was similar in both wetlands (17,442 seeds m−2 vs. 17,000 seeds m−2). Opportunistic seagrass Ruppia maritima was observed in both wetlands, with higher abundance in summer when Z. marina disappears due to high water temperatures. Eelgrass coverage was three orders of magnitude greater in the CIF (9725 ha) than in BCP (3 ha). The striking difference between these wetlands is the lack of environmental protection for BCP and the protection of the CIF by the Seri indigenous community, which increases human pressure in the former, putting it at high risk of disappearing. Conservation of eelgrass meadows is not only necessary to preserve their ecosystem services but to insure the survival of migratory populations (Pacific brant goose, Branta bernicla), endangered species (Black turtle, Chelonia mydas), and fisheries-related species.