Amount Of Natural Habitat Research Articles

Topography, more than land cover, explains genetic diversity in a Neotropical savanna tree frog

AbstractAimEffective conservation policies rely on information about population genetic structure and the connectivity of remnants of suitable habitats. The interaction between natural and anthropogenic discontinuities across landscapes can uncover the relative contributions of different barriers to gene flow, with direct consequences for decision‐making in conservation. We aimed to quantify the relative roles of land cover and topographic variables on the population genetic differentiation and diversity of a stream‐breeding savanna tree frog (Bokermannohyla ibitiguara) across its range.LocationSerra da Canastra mountain range, Cerrado of Minas Gerais State, Brazil.MethodsWe collected samples and extracted DNA samples from 12 populations within and outside a strictly protected park, and used 17 microsatellite markers to assess genetic structure, among‐population differentiation and within‐population diversity measures. We incorporated landscape data derived from digital models and satellite images to create connectivity matrices to correlate with genetic differentiation using Mantel tests. We used generalized linear models and path analyses to assess the roles of each landscape variable in shaping genetic diversity in this species.ResultsPopulations within and outside the park boundaries belonged to four genetic clusters. Most populations showed evidence of limited gene flow, with significant genetic differentiation, except for those within the park, which also had higher levels of allelic richness and heterozygosity. However, genetic differentiation among populations in this landscape was primarily explained by topographic complexity. Likewise, within‐population measures of genetic diversity were best explained by models including elevation and topographic complexity, and not the amount of natural habitat or gallery forests.Main conclusionsOur results underscore that topography may be a strong historical factor shaping genetic structure among amphibian populations. Therefore, effective conservation strategies for endangered amphibians should avoid focusing exclusively on habitat suitability, and incorporate topographic complexity, which seems to be a key factor for the fauna of the extremely threatened Brazilian savanna.

Heating a biodiversity hotspot: connectivity is more important than remaining habitat

Connectivity, which is a fundamental aspect of any landscape, has been shown to have a nonlinear relationship with the amount of natural habitat, with a marked decrease at intermediate levels of coverage. Impacts on connectivity vary according to how natural habitat is removed. We analyzed connectivity in the Brazilian Cerrado (tropical savanna), a 2 million-km2 biodiversity hotspot. We evaluated the effects of habitat removal on connectivity, hypothesizing that a deforestation threshold exists below which connectivity is drastically reduced and that neighboring landscapes have similar patterns of connectivity. We divided the Cerrado into 624 50 × 50 km cells and used the integral index of connectivity (IIC), available in Conefor software, to evaluate changes in connectivity between 2000 and 2017. We analyzed how the intra, flux, and connector components of connectivity vary with changes in percentage of remaining natural habitat. Between 2000 and 2017, 23.9% of the natural habitat of the Cerrado was lost (~ 254,000 km2) and connectivity decreased significantly (W = 179,700, p < 0.01). The most crucial change was the removal of connector fragments or corridors, which occurred in 78.2% of the landscapes. The relationship between IIC and remaining natural area revealed a breakpoint, when native area in a landscape reached 39% in 2000 and 37% in 2017. Regardless of the spatial arrangement of habitat fragments, landscape connectivity is lost when the remaining natural habitat falls below a certain threshold. More restrictive regulations and government permissions should be considered to avoid over-occupation of landscapes.

Harvesting effects on wild bee communities in bioenergy grasslands depend on nesting guild.

Conversion of annual crops to native perennial grasslands for bioenergy production may help conserve wild bees by enhancing nest and food resources. However, bee response to the disturbance of biomass harvesting may depend on their nesting location, thus their vulnerability to nest destruction, and the response of the forb community on which they forage. Moreover, because bees have long foraging ranges, effects of local harvesting may depend on the amount of natural habitat in the surrounding landscape. We performed a large-scale one- and two-year experiment in Michigan and Wisconsin, USA, respectively, to examine how grassland harvesting, landscape context, and study year affect the forb community, above- and belowground-nesting bee species richness, community composition, trap nest emergence, and visitation rate. In Wisconsin, harvesting increased forb richness, cover, and evenness compared to unharvested control sites. Harvesting negatively affected aboveground-nesting bee richness and emergence from trap nests, possibly because of nest destruction during the previous harvest. By contrast, harvesting positively affected belowground-nesting bee richness, possibly because of the greater food resource availability and reduced thatch allowing greater access to nesting sites in the soil. Harvesting also affected bee community composition, reflecting the increase in belowground-nesting species at harvested sites. Despite harvesting effects on forb and bee communities, there was no effect on flower visitation rate, indicating little effect on pollination function. We did not find a harvest by landscape context interaction, which, in combination with the negative harvesting effect on trap nest emergence, suggests that harvesting can affect local population growth rather than simply affecting forager aggregation in different resource environments. For bees, there was no harvest by study year interaction, indicating a consistent response over a short timescale. Similarly, in Michigan, belowground-nesting species also responded positively to harvesting, which was more pronounced in sandier soils that are preferred for nesting. However, other components of the Michigan bee and forb communities were not significantly affected by biomass harvesting. Overall, our study demonstrates that harvesting grasslands can positively affect the ~80% of bee species that nest belowground by enhancing nest and/or forage resources, but that conserving aboveground nesters may require leaving some area unharvested.

Drivers of species richness and community integrity of small forest patches in an agricultural landscape

AbstractQuestionsLong‐term fragmentation and land use in Europe have created a landscape pattern where small forest patches are embedded among agricultural landscapes. These small forest patches can be one of the few habitats left to maintain the species richness and ecosystem functions within intensively managed agroecosystems. We ask, which factors determine vascular plant species richness, community composition and forest community integrity in small forest patches in an agricultural landscape?LocationNE Estonia.MethodsWe combine island biogeographic theory (patch area and isolation) with the properties of the surrounding landscape and local environmental conditions within a patch to study the drivers of species richness and community integrity.ResultsPatch area together with local environmental factors (understorey light conditions and soil reaction) determined both species richness and community integrity. Total species richness and forest generalists were related to patch area alone, whereas forest specialists were additionally dependent on patch light conditions. Species richness of grassland specialists in the forest patches increased with the amount of natural habitat in the surrounding landscape, while the presence of synanthropic species was positively related to soil reaction. Forest community integrity was higher in larger, more shaded patches with low soil reaction, which together defined suitable conditions for forest communities and hindered the intrusion of species from other habitats.ConclusionsUnder a suitable set of conditions, encompassing both favourable landscape and local environmental conditions, even small forest patches can provide habitat for both forest and grassland communities in agricultural landscapes. Comprehensive approaches, considering species composition, environment and landscape conditions simultaneously, are needed for making reliable predictions of biodiversity patterns.

The Potential Influence of Bumble Bee Visitation on Foraging Behaviors and Assemblages of Honey Bees on Squash Flowers in Highland Agricultural Ecosystems.

Bee species interactions can benefit plant pollination through synergistic effects and complementary effects, or can be of detriment to plant pollination through competition effects by reducing visitation by effective pollinators. Since specific bee interactions influence the foraging performance of bees on flowers, they also act as drivers to regulate the assemblage of flower visitors. We selected squash (Cucurbita pepo L.) and its pollinators as a model system to study the foraging response of honey bees to the occurrence of bumble bees at two types of sites surrounded by a high amount of natural habitats (≥ 58% of land cover) and a low amount of natural habitats (≤ 12% of land cover) in a highland agricultural ecosystem in China. At the individual level, we measured the elapsed time from the departure of prior pollinator(s) to the arrival of another pollinator, the selection of honey bees for flowers occupied by bumble bees, and the length of time used by honey bees to explore floral resources at the two types of sites. At the community level, we explored the effect of bumble bee visitation on the distribution patterns of honey bees on squash flowers. Conclusively, bumble bee visitation caused an increase in elapsed time before flowers were visited again by a honey bee, a behavioral avoidance by a newly-arriving honey bee to select flowers occupied by bumble bees, and a shortened length of time the honey bee takes to examine and collect floral resources. The number of overall bumble bees on squash flowers was the most important factor explaining the difference in the distribution patterns of honey bees at the community level. Furthermore, decline in the number of overall bumble bees on the squash flowers resulted in an increase in the number of overall honey bees. Therefore, our study suggests that bee interactions provide an opportunity to enhance the resilience of ecosystem pollination services against the decline in pollinator diversity.

Sharing enemies: evidence of forest contribution to natural enemy communities in crops, at different spatial scales

Abstract The increase in cultivated lands has led to ecosystem and biodiversity loss. Arthropod natural enemies, involved in the ecosystem service of biological control, benefit from non‐crop habitat and may be affected by its proximity and amount in the landscape. We have evaluated natural enemy richness and composition in relation to forest cover in the landscape and distance from the forest, for a Chaco Serrano forest‐soybean crop system. Forest contribution to natural enemies on soybean was also investigated, by assessing similarities between forest and crop assemblages, and examining body size of shared enemies in relation to distance from the forest. In nine landscape circles, yellow pan traps were placed in forest and soybean crops (5, 25, 50 and 100 m from forest edge), which collected 8041 specimens representing 290 species. Species richness of natural enemies was positively related to forest cover and declined from the forest to the furthermost soybean locations, with both forest cover and its proximity affecting community composition. Also, similarity of forest and crop assemblages increased with forest cover and proximity. Finally, forest‐crop shared assemblages showed larger average body size at greater distances from the forest, indicating dispersal limitations on forest contribution to the crop. Our results suggest that forest species are important components of natural enemy communities on soybean, and that both the amount of natural habitat and its proximity may influence agroecosystems. We emphasise the importance of non‐crop habitat to help maintain natural enemy communities and ensure the ecosystem service of pest control.

Different responses of bees and hoverflies to land use in an urban–rural gradient show the importance of the nature of the rural land use

Most studies focusing on the effects of urban land use on pollinators have compared urban sites with one type of rural site. However, there is a lot of variation in the amount of natural habitats or intensive agriculture in rural areas. The position of urban areas within that continuum in terms of pollinator communities remains unclear. In this work, we studied bee and hoverfly communities (abundance, diversity, and species composition) in three site types along two river systems crossing urban areas, rural areas dominated by agriculture (termed rural-agricultural) and rural areas with high amounts of semi-natural land use (termed rural-natural). Pollinators were caught in August 2011. Abundance and diversity were highest in rural-natural sites for both taxonomic groups. Our data also indicate that hoverflies and bees responded differently to the surrounding land use, with bee abundance and diversity only significantly reduced in rural-agricultural sites but not in urban sites, and hoverfly abundance and diversity only significantly reduced in urban sites but not in rural-agricultural sites. The observed differences in the response of pollinators point out the importance of incorporating different types of rural land use and clearly defining the rural end of an urban–rural gradient in getting a clear view on how urban land use affects a specific pollinator group. Year-round sampling of these pollinators would, however, probably enable a more accurate view on these responses.