Species Richness In Fragments Research Articles

Hummingbird diversity in a fragmented tropical landscape in the Chocó biogeographic zone

AbstractForest loss and fragmentation drive widespread declines in biodiversity. However, hummingbirds seem to exhibit relative resilience to disturbance, characterized by increasing abundance alongside declining species richness and evenness. Yet, how widespread this pattern may be, and the mechanisms by which it may occur, remain unclear. To fill in this knowledge gap, we investigated habitat‐ and site‐level patterns of diversity, and community composition of hummingbirds between continuous forest (transects n = 16 in ~3500 ha) and more disturbed surrounding fragments (n = 39, 2.5–48.0 ha) in the Chocó rain forest of northwestern Ecuador. Next, we assessed within‐patch and patch‐matrix characteristics associated with hummingbird diversity and composition. We found higher hummingbird species richness in forest fragments relative to the continuous forest, driven by increased captures of rare species in fragments. Community composition also differed between continuous forest and fragments, with depressed evenness in fragments. Increased canopy openness and density of medium‐sized trees correlated with hummingbird diversity in forest fragments, although this relationship became nonsignificant after applying false discovery rate (p < .01). Higher species richness in fragments and higher evenness in the continuous forest highlight the complex trade‐offs involved in the conservation of this ecologically important group of birds in changing Neotropical landscapes.Abstract in Spanish is available with online material.

Contrasting edge and pasture matrix effects on ant diversity from fragmented landscapes across multiple spatial scales

Harmful effects of habitat loss and fragmentation can be detected across multiple spatial scales, yet most studies that aim to characterize these effects take place at a single spatial scale. Here we investigated responses in ant diversity to forest fragmentation across three spatial scales. We sampled ant diversity in a fragmented landscape in southeastern Brazil. We set transects with 15 pitfall traps (local scale response) within 16 forest fragments (fragment scale response) distributed in eight paired fragments separated by roads (mesoscale response). We measured habitat features at local, fragment and mesoscales and across the landscape. For each spatial scale, we then assessed the effects of ecological drivers measured at the same and subsequent higher spatial scales. Local diversity was higher with closer proximity to the matrix, and in fragments with high vegetation density. Both fragment species richness and β-diversity were higher in less circular fragments. However, at the mesoscale (pairs of fragments), total species richness decreased with increasing pasture matrix in the landscape (landscape driver). Edge and matrix effects lead to increased ant species richness at small spatial scales (due to an increase in generalist ants). However, when analyzed at a higher spatial scale, the responses to these effects were in fact reversed, leading to a decrease in ant diversity. Thus, we suggest that conservation efforts should take a multi-scale perspective (from local to landscape) and aim to protect both local and fragment characteristics that can buffer edge effects, as well as improve matrix quality in the landscape.

Successional status, seed dispersal mode and overstorey species influence tree regeneration in tropical rain-forest fragments in Western Ghats, India

Abstract:The effects of fragmentation and overstorey tree diversity on tree regeneration were assessed in tropical rain forests of the Western Ghats, India. Ninety plots were sampled for saplings (1–5 cm diameter at breast height (dbh); 5×5-m plots) and overstorey trees (>9.55 cm dbh; 20×20-m plots) within two fragments (32 ha and 18 ha) and two continuous forests. We tested the hypotheses that fragmentation and expected seed-dispersal declines (1) reduce sapling densities and species richness of all species and old-growth species, and increase recruitment of early-successional species, (2) reduce the prevalence of dispersed recruits and (3) increase influence of local overstorey on sapling densities and richness. Continuous forests and fragments had similar sapling densities and species richness overall, but density and richness of old-growth species declined by 62% and 48%, respectively, in fragments. Fragments had 39% lower densities and 24% lower richness of immigrant saplings (presumed dispersed into sites as conspecific adults were absent nearby), and immigrant densities of old-growth bird-dispersed species declined by 79%. Sapling species richness (overall and old-growth) increased with overstorey species richness in fragments, but was unrelated to overstorey richness in continuous forests. Our results show that while forest fragments retain significant sapling diversity, losses of immigrant recruits and increased overstorey influence strengthen barriers to natural regeneration of old-growth tropical rain forests.

Partitioning the effects of habitat fragmentation on rodent species richness in an urban landscape

Habitat fragmentation plays a major role in species extinction around the globe. Previous research has determined that species richness in fragments is affected by a number of characteristics. These include fragment age, size, and isolation, edge effects, vegetation coverage, habitat heterogeneity, and matrix content. Although most studies focused on one or a few of these characteristics, multiple characteristics work together to affect species richness, showing that the effects of habitat fragmentation are complex. The goal of our study was to partition the complex effects of habitat fragmentation by determining the direct, indirect, and cumulative effects of multiple habitat fragment characteristics on rodent species richness. In 2013, we determined rodent species richness in 25 habitat fragments within Thousand Oaks, California. In addition, we measured the following characteristics for each fragment: fragment age, area, isolation, shrub coverage, habitat heterogeneity, perimeter/area ratio, and percent non-urban buffer. Path Analysis was used to test the hypothesized model which described the direct, indirect, and cumulative effect of each habitat fragment characteristic on rodent species richness. Overall, the path model explained 67 % of the variation in rodent species richness among habitat fragments. Habitat heterogeneity had the greatest direct and total effect on rodent species richness. Fragment size had the next greatest total effect on rodent species richness but this was nearly entirely indirect through its influence on habitat heterogeneity, suggesting that large fragments containing the greatest diversity of habitats will support the most species. Our study shows that large habitat fragments support the greatest habitat diversity, which provides the highest likelihood of conserving rodent species richness in an urban landscape.

Forest fragmentation in an African biodiversity hotspot impacts mixed-species bird flocks

The effect of forest fragmentation on mixed-species foraging bird flocks has been poorly evaluated, particularly in African forests. We examined the consequences of forest fragmentation on such flocks in the East Usambara Mountains, Tanzania, by addressing ecological as well as behavioral components. We counted these flocks in five small (<31ha), isolated fragments and six widely spaced continuous forest sites. Given that flock cohesion and stability might be facilitated via positive interactions of leader or nuclear species, we focused on one putative nuclear species, the square-tailed drongo (Dicrurus ludwigii), and using playback of its vocalisations, we evaluated (i) if its vocalisations attracted flocking birds as expected by a nuclear species, and (ii) if loss of this species in fragments contributed to flock declines. We found that flocks in forest fragments had smaller sizes, reduced species richness, a reduced proportion of understorey specialists, a higher proportion of forest generalists and non-forest species, and were more variable in size and composition compared to flocks observed in continuous forest. Furthermore, flocks in fragments were composed of a higher proportion of omnivores than insectivores. Despite lower absolute abundance in fragments, D. ludwigii was observed in 86% of natural occurring flocks in both fragments and continuous forest, and flocks with D. ludwigii were significantly larger than those without it––especially in the continuous forest. Playback vocalisations of D. ludwigii attracted flocks of similar abundance and species richness in fragments and continuous forest, but a vastly different composition, confirming (i) its nuclear role and (ii) that, in fragments, flock assemblages had a distinct composition, with a high proportion of forest generalists and non-forest species. Loss or diminished abundance of nuclear species due to fragmentation may be an important factor that affects the presence and composition of mixed-species flocks. Given that 67% of flocking species forage in the understorey, and that insectivores were more negatively affected in fragments than omnivores, the implications of our findings are relevant for conservation in tropical forests.

Parallel declines in species and genetic diversity in tropical forest fragments

The potential for parallel impacts of habitat change on multiple biodiversity levels has important conservation implications. We report on the first empirical test of the 'species-genetic diversity correlation' across co-distributed taxa with contrasting ecological traits in the context of habitat fragmentation. In a rainforest landscape undergoing conversion to oil palm, we show that depauperate species richness in fragments is mirrored by concomitant declines in population genetic diversity in the taxon predicted to be most susceptible to fragmentation. This association, not seen in the other species, relates to fragment area rather than isolation. While highlighting the over-simplification of extrapolating across taxa, we show that fragmentation presents a double jeopardy for some species. For these, conserving genetic diversity at levels of pristine forest could require sites 15-fold larger than those needed to safeguard species numbers. Importantly, however, each fragment contributes to regional species richness, with larger ones tending to contain more species.

Panorama da araneofauna de fragmentos florestais em Salvador, Bahia, Brasil

This study aimed to compose a species database of the spider fauna in seven urban fragments of Atlantic Forest in Salvador city, State of Bahia, comparing the composition of three of those remaining fragments. The data were gathered in the Arachnology collection of the Animal Ecology and Conservation Centre (ECOA) – UCSal, coming from several projects connected to the centre between 2000 and 2009. We identified 3,201 adult individuals, from 39 families, 143 genera and 170 species or morphospecies. There was significant difference in the species composition of the spider fauna between the three fragments (Botanical Garden of Salvador, the Joventino Silva Park and forest within the ground of the 4th Guard Company). The species richness of fragments in Salvador has been found to be low, but standardized surveys of spiders are still needed to demonstrate the importance of conservation of the green areas within the city, since they maintain the diversity of the araneo-fauna in Salvador.

Araneofauna sinantrópica associada com a família Sicariidae no município de União da Vitória, Paraná, Brasil

This study aimed to compose a species database of the spider fauna in seven urban fragments of Atlantic Forest in Salvador city, State of Bahia, comparing the composition of three of those remaining fragments. The data were gathered in the Arachnology collection of the Animal Ecology and Conservation Centre (ECOA) – UCSal, coming from several projects connected to the centre between 2000 and 2009. We identified 3,201 adult individuals, from 39 families, 143 genera and 170 species or morphospecies. There was significant difference in the species composition of the spider fauna between the three fragments (Botanical Garden of Salvador, the Joventino Silva Park and forest within the ground of the 4th Guard Company). The species richness of fragments in Salvador has been found to be low, but standardized surveys of spiders are still needed to demonstrate the importance of conservation of the green areas within the city, since they maintain the diversity of the araneo-fauna in Salvador.

A multi‐scale analysis of fragmentation effects on remnant plant species richness in Phoenix, Arizona

AbstractAim Understanding complex ecological phenomena, such as the determinants of species richness, is best achieved by investigating their properties at different spatial scales. Factors significantly affecting the number of species occurring at one scale may not impact on richness at other scales. While this scale dependence has become increasingly recognized, there still remains a need to elucidate exactly how richness is structured across scales, and which mechanisms are influential for determining this important community property. This study explores how woody plant species richness varies in a fragmented system at multiple scales, and which factors are primarily responsible for these patterns.Location The study area is located in the Sonoran Desert within the bounds of metropolitan Phoenix, Arizona, which is the locus of the Central Arizona–Phoenix Long‐Term Ecological Research (CAP‐LTER) site.Methods Estimates of local and fragment plant species richness were generated from field data collected from 22 sites. Independent variables describing fragment sites were also calculated, including area, habitat heterogeneity, density of individuals, mean elevation, and extent of isolation. Structural equation modelling, multiple regression, and analysis of covariance were used to assess the contribution of independent variables to richness at the fragment and local scales.Results Fragment species richness was significantly influenced by area, though not isolation, habitat heterogeneity, mean elevation, or density of individuals. Local richness was not significantly related to fragment area, but was positively related to fragment richness, plant density, and elevation.Main conclusions The fragment species–area effect resulted from larger remnants supporting higher numbers of individuals at comparable densities, increasing richness through either passive sampling of progressively less common species and/or lower extinction rates among larger populations. Without using multi‐temporal data it is not possible to disentangle these mechanisms. We found that patterns evident at one scale are not necessarily apparent at other scales, as elevation and density of individuals significantly affected richness at the local scale but not at the fragment scale. These results lend support to the concept that mechanisms influencing the species richness of natural communities may be operable only within certain domains and that relevant scales should be specified.

Changes to plant species richness in forest fragments: fragment age, disturbance and fire history may be as important as area

AimThe impact of fragmentation on a eucalypt forest was investigated by examining the effects of fragment size, time since fragmentation, degree of anthropogenic disturbance to fragment interiors, and time since fire, on native and exotic plant species richness per unit area.LocationTwo areas of dry open‐forest were studied on the central coast of New South Wales in south‐eastern Australia. Fifty forest fragments were located at Tomago, an area progressively fragmented over the last 60 years, most recently by clearing for sand‐mining. Also at Tomago were six very large blocks of forest that were used as reference sites. The second area at Myall Lakes National Park (50 km north of Tomago) had four very large areas of intact forest that were also used as reference sites.MethodsFragments were allocated into (1) three size classes: small (&lt;1 ha), medium (1 to &lt;10 ha) and large (10 to &lt;100 ha); (2) two classes of age since fragmentation: young (up to 10 years) and old (10 years or more); (3) two classes of disturbance (minor, major) based on the degree and extent of human‐induced disturbance to the fragment interior; and (4) two classes of time since fire (between 5 and 6 years; 10 years or more). Reference sites belonged to a very large size class (&gt;100 ha). Mean plant species richness per 25 m2 area was determined for each fragment and analysed separately for native and exotic species.ResultsThe most significant effects observed resulted from anthropogenic disturbance. In fragments with major disturbance, native species richness per unit area was significantly reduced in small‐sized young and medium‐sized old fragments. A significant increase was also observed for exotic species richness in fragments with major disturbance. With minor disturbance, native species richness in small fragments declined significantly with time since fragmentation, in contrast to medium and large fragments. Among recently created fragments, those recently burned had significantly more native species per unit area than those burned 10 or more years ago.Main conclusionsAnthropogenic disturbance coupled with fragmentation had a stronger and more immediate effect in reducing native species richness and increasing exotic species richness than did fragmentation alone. In the absence of major disturbance, small fragments had fewer native species than larger size classes, but only after 10 or more years since fragmentation, confirming the importance of controlling for age of fragments when examining species–area relationships. This study has not tested whether differences in area were the direct cause of this loss of species over time; other factors that are correlated with area (such as edge effects) may also be involved. The increase in native species richness following fire was consistent with other studies of fire in unfragmented eucalypt forest. This study thus shows that in addition to the factors emphasized in classical island biogeography models, fragment age, disturbance and fire history are important in explaining species richness in fragmented eucalypt forests.