The gharial (Gavialis gangeticus Gmelin) is a fish-eating specialist crocodylian, endemic to south Asia, and critically endangered in its few remaining wild localities. A secondary gharial population resides in riverine-reservoir habitat adjacent to the Nepal border, within the Katerniaghat Wildlife Sanctuary (KWS), and nests along a 10 km riverbank of the Girwa River. A natural channel shift in the mainstream Karnali River (upstream in Nepal) has reduced seasonal flow in the Girwa stretch where gharials nest, coincident with a gradual loss of nest sites, which in turn was related to an overall shift to woody vegetation at these sites. To understand how these changes in riparian vegetation on riverbanks were related to gharial nesting, we sampled vegetation at these sites from 2017 to 2019, and derived an Enhanced Vegetation Index (EVI) from LANDSAT 8 satellite data to quantify riverside vegetation from 1988 through 2019. We found that sampled sites transitioned to woody cover, the number of nesting sites declined, and the number of nests were reduced by > 40%. At these sites, after the channel shift, woody vegetation replaced open sites that predominated prior to the channel shift. Our findings indicate that the lack of open riverbanks and the increase in woody vegetation at potential nesting sites threatens the reproductive success of the KWS gharial population. This population persists today in a regulated river ecosystem, and nests in an altered riparian habitat which appears to be increasingly unsuitable for the continued successful recruitment of breeding adults. This second-ranking, critically endangered remnant population may have incurred an "extinction debt" by living in a reservoir that will lead to its eventual extirpation.
1. The biotic resistance hypothesis suggests that biodiversity-rich areas should be resistant to biological invasions. Globally, conservationists use this hypothesis to protect diverse ecosystems. However, supporting data are often contradictory, possibly due to several confounding factors. Complexity in inferences increases in the tropics, which are sparsely studied.2. We hypothesize that human impacts, forest type and climate would modulate the relationship between native and invasive plant richness. To understand these interacting and varying effects of native richness and human disturbance on plant invasions, we sampled 354 grids of 25 km 2 with equal representation of protected areas (PAs) and multi-use areas (MAs) to record abundance of native and nonnative plants from 34 PAs across five forest types in tropical India. We used linear mixed effect models to investigate the occurrence and abundance of invasive plants with respect to varying native richness, human impacts, forest types and climate.3. Human use of forests increased the richness and abundance of invasive plants across all forest types. After accounting for human use, native species richness of tropical wet forests had a negative relationship with invasive plants richness and abundance, while the relationship reversed with increasing aridity and temperature. Human infrastructure facilitated invasions within PAs.
Synthesis.The biotic resistance hypothesis explained a lower number of invasions within protected tropical wet forests but not within dry forests. Humanfree protected areas had lower richness and abundance of invasive plants across all systems, especially in wet tropical forests. Our results support the contextual importance of the biotic resistance hypothesis, while stressing the importance of protected areas, insulated from human impacts, to preserve the integrity of vulnerable natural systems.
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As climate conditions continue to shift, species assemblages and composition within ecological communities may be reshuffled in unpredictable ways. Some habitat types may cease to exist while others may expand in size; protecting ecosystems and species in their current locations will become increasingly difficult. Threatened and endangered species are likely to be disproportionately affected by climate change because they are often habitat specialists and relatively rare. In the United States, the 1973 Endangered Species Act has prevented the extinction of many species. The identification and conservation of critical habitat is an important tool for species preservation. But how do we designate and preserve habitat for protected species when we are unsure about future habitat conditions? We address this question based upon the concept of managing for anticipated change, rather than focusing on the maintenance of existing conditions. We used an ecological niche modeling program (MaxEnt) to model current and future climatic niche for an endangered mammal endemic to southern California, USA; the Stephens' kangaroo rat (SKR, Dipodomys stephensi). Our results indicate that the climatic niche of SKR was governed primarily by precipitation during the dry season, precipitation seasonality, annual mean temperature, and mean summer temperature. Projecting current species-presence relationships to different scenarios predicted for the future revealed substantial loss in climatic niche with increased emission rates. Areas of future suitable climatic niche were evaluated in relation to land ownership and identified as potential reserves or translocation sites, which can aid in conservation planning for this species. Additionally, species vulnerability assessments and a climate-change analysis tool were utilized to demonstrate how overall understanding of climate change effects can be enhanced. Information presented here can serve as guiding principles for the inclusion of climate change considerations into management plans, and can better inform overall decision-making related to endangered species management. Ó
The extension of the Asian Elephant’s Elephas maximus range in the northern Western Ghats (Sahyadri) was observed since 2002. This colonization was marked by elephant crop raiding events in the newly colonized Sindhudurg District, where the local community had no experience of living with elephants. The present study was conducted to understand the spatiotemporal patterns of crop depredation (raiding) and to prioritize areas to inform future interventions on managing this ecological phenomenon turned conflict. Data on crop raiding between 2002 and 2015 was obtained from compensation records with the state forest department, and mapped at village scale. Subsequently, we used three indices of crop raiding, viz., Crop Raiding Frequency (CRF), Relative Crop Raiding Intensity (RCRI), and Crop Raiding Vulnerability Index (CRVI). Results show a gradual northern movement of elephants and of the crop raiding zone over the period of 2002–2015. The rankings provided by CRVI, identified villages in a narrow strip of foothills of the Sahyadri mountains as severely vulnerable. With sufficient long term data, CRVI would be a highly useful index for prioritization of villages for resolving human-elephant negative interactions; and other cases of human-wildlife interactions too.
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