scholarly journals The Habitat Amount Hypothesis implies negative effects of habitat fragmentation on species richness and occurrence

2020 ◽  
Author(s):  
Santiago Saura
Keyword(s):  
Species Richness ◽  
Habitat Fragmentation ◽  
Spatial Configuration ◽  
Spatial Scales ◽  
Conservation Strategies ◽  
Negative Effects ◽  
Habitat Amount ◽  
Habitat Configuration ◽  
Habitat Amount Hypothesis ◽  
Individual Site

AbstractThe Habitat Amount Hypothesis (HAH) predicts that species richness, abundance or occurrence in a habitat site increases with the amount of habitat in the ‘local landscape’ defined by an appropriate distance around the site, with no distinct effects of the size of the habitat patch in which the site is located. It has been stated that a consequence of the HAH, if supported, would be that it is unnecessary to consider habitat configuration to predict or manage biodiversity patterns, and that conservation strategies should focus on habitat amount regardless of fragmentation. Here, I assume that the HAH holds and apply the HAH predictions to all habitat sites over entire landscapes that have the same amount of habitat but differ in habitat configuration. By doing so, I show that the HAH actually implies clearly negative effects of habitat fragmentation, and of other spatial configuration changes, on species richness, abundance or occurrence in all or many of the habitat sites in the landscape, and that these habitat configuration effects are distinct from those of habitat amount in the landscape. I further show that, contrary to current interpretations, the HAH is compatible with a steeper slope of the species-area relationship for fragmented than for continuous habitat, and with higher species richness or abundance for a single large patch than for several small patches with the same total area (SLOSS). This suggests the need to revise the ways in which the HAH has been interpreted and can be actually tested. The misinterpretation of the HAH has arisen from confounding and overlooking the differences in the spatial scales involved: the individual habitat site at which the HAH gives predictions, the local landscape around an individual site, and the landscapes or regions (with multiple habitat sites and different local landscapes) that need to be analysed and managed. The HAH has been erroneously viewed as negating or diminishing the relevance of fragmentation effects, while it actually supports the importance of habitat configuration for biodiversity. I conclude that, even in the cases where the HAH holds, habitat fragmentation and configuration are important for understanding and managing species distributions in the landscape.

scholarly journals Influence of landscape structure on Euglossini composition in open vegetation environments

2017 ◽  
Vol 17 (1) ◽  
Author(s):  
Eduardo Freitas Moreira ◽  
Rafaela Lorena da Silva Santos ◽  
Maxwell Souza Silveira ◽  
Danilo Boscolo ◽  
Edinaldo Luz das Neves ◽  
...  
Keyword(s):  
Species Richness ◽  
Landscape Structure ◽  
Multiple Scales ◽  
Landscape Heterogeneity ◽  
Species Abundance ◽  
Information Criterion ◽  
Landscape Configuration ◽  
Habitat Amount ◽  
Savanna Vegetation ◽  
Habitat Amount Hypothesis

Abstract The fauna of Euglossini bees is poorly known in savanna regions, making it difficult to understand how these bees use open vegetation environments. The aim of this study was to evaluate the influence of landscape structure on species abundance and composition of Euglossini bees in naturally heterogeneous savanna landscapes. Nine sites were sampled monthly using six traps with chemical baits. Three aromatic essences (eucalyptol, methyl salicylate and vanillin) were used to attract the Euglossini. Surrounding environmental conditions were measured using three independent variables, calculated in multiple scales: index of local vegetation and two landscape indices (Shannon Diversity and area-weighted shape). We compared the competing hypotheses through model selection based on Second-order Akaike Information Criterion (AICc). The four competing hypothesis were: (1) The local vegetation complexity favors Euglossini bees species richness and/or abundance (local vegetation hypothesis); (2) The proportion of the native vegetation types favors Euglossini bees species richness and/or abundance (habitat amount hypothesis); (3) Higher landscape diversity shall increase species richness of Euglossini bees (landscape heterogeneity hypothesis); (4) More complex landscape configuration shall favor the Euglossini bees richness and/or abundance (landscape heterogeneity hypothesis). We sampled 647 individuals belonging to six species of two distinct genera. Our results support the habitat amount hypothesis since bees’ abundance was strongly related with the proportion of habitat in the surrounding landscape. This may be related to the availability of floral and nesting resources in some types of savanna vegetation.

scholarly journals Vegetation structure as the main source of variability in scorpion assemblages at small spatial scales and further considerations for the conservation of Caatinga landscapes

2020 ◽  
Vol 15 (4) ◽  
pp. 533-550
Author(s):  
Stênio Ítalo Araújo Foerster ◽  
André Felipe de Araújo Lira ◽  
Cauê Guion de Almeida
Keyword(s):  
Species Richness ◽  
Vegetation Structure ◽  
Habitat Complexity ◽  
Environmental Changes ◽  
Spatial Scales ◽  
Abiotic Factors ◽  
Terrestrial Ecosystems ◽  
Conservation Strategies ◽  
Dispersal Ability ◽  
Environmental Complexity

Even at the local scale, environmental changes due of anthropogenic actions represent a source of disturbance in terrestrial ecosystems, forcing species to respond according to their ecological plasticity. Thus, stenotopic species and those with low-dispersal ability will likely be negatively affected by landscape modifications that reduce environmental complexity. In this study, we identify and quantify the effects of biotic and abiotic factors related to habitat complexity on the variation in scorpion assemblages in terms of both species’ richness, abundance and composition across 18 transects covering Caatinga landscapes with different levels of degradation. Using ultraviolet flashlights, we sampled 269 scorpions, belonging to six species and two families. The results showed contrasting patterns of species richness and abundance that depend on the level of habitat complexity. More specifically, we reported that scorpion species richness could be predicted by the number of trees, while the coefficient of variation of the diameter at breast height of trees (cvDBH) is a predictor of scorpion abundance. These findings suggest that vegetation structure is deterministic for the maintenance of scorpion assemblages in Caatinga landscapes. In addition, the cvDBH and tree number may explain 39% and 40% of the variability observed amongst scorpion assemblages in terms of richness difference and species composition, respectively. This study provides insights concerning the development of conservation strategies, clarifying the role of habitat complexity for the preservation of low-dispersal animals in neglected environments, such as those within the Caatinga domain.

scholarly journals Seascape connectivity exerts differing effects for fish assemblages in distinct habitats of the surf zones of ocean beaches

2020 ◽  
Vol 77 (3) ◽  
pp. 1033-1042
Author(s):  
Jesse D Mosman ◽  
Christopher J Henderson ◽  
Andrew D Olds ◽  
Ben L Gilby ◽  
Thomas A Schlacher
Keyword(s):  
Species Richness ◽  
Indicator Species ◽  
Surf Zone ◽  
Fish Assemblages ◽  
Spatial Configuration ◽  
Spatial Scales ◽  
Coastal Habitat ◽  
Rocky Reefs ◽  
Eastern Australia ◽  
Management Approaches

Abstract Animals move throughout coastal seascapes to disperse, feed, and spawn, including the surf zones of ocean beaches. Yet, the influences of seascape context on surf-zone fish are largely unquantified. We sampled surf-zone fish assemblages with baited remote underwater video deployments at 25 beaches across 50 km of coastline in eastern Australia to determine if variation in the spatial configuration of broader coastal seascapes shapes fish assemblages in different surf-zone habitats. We show that surf zones are not homogenous fish habitats, with offshore bars and nearshore troughs having distinct fish assemblages, shaped by different environmental variables. Fish assemblages of offshore bars were characterized by greater species richness and a higher abundance of indicator species (as identified by Dufrene–Legendre indicator species analysis) when close to rocky reefs and estuaries. In contrast, fish assemblages of nearshore troughs were characterized by greater species richness and a higher abundance of indicator species when far from estuaries, and off wider beaches. Our results highlight the importance of seascape connectivity in structuring surf-zone fish assemblages. Consequently, management approaches need to more thoroughly quantify the effects of seascape connectivity over smaller spatial scales and consider surf zones as key components of broader coastal habitat mosaics.

scholarly journals Saproxylic species are linked to the amount and isolation of dead wood across spatial scales in a beech forest

2020 ◽  
Author(s):  
Elena Haeler ◽  
Ariel Bergamini ◽  
Stefan Blaser ◽  
Christian Ginzler ◽  
Karin Hindenlang ◽  
...  
Keyword(s):  
Species Richness ◽  
Spatial Scale ◽  
Beta Diversity ◽  
Dead Wood ◽  
Spatial Scales ◽  
Beech Forest ◽  
Habitat Amount ◽  
Alpha And Beta Diversity ◽  
Local Species Richness ◽  
Saproxylic Species

Abstract Context Dead wood is a key habitat for saproxylic species, which are often used as indicators of habitat quality in forests. Understanding how the amount and spatial distribution of dead wood in the landscape affects saproxylic communities is therefore important for maintaining high forest biodiversity. Objectives We investigated effects of the amount and isolation of dead wood on the alpha and beta diversity of four saproxylic species groups, with a focus on how the spatial scale influences results. Methods We inventoried saproxylic beetles, wood-inhabiting fungi, and epixylic bryophytes and lichens on 62 plots in the Sihlwald forest reserve in Switzerland. We used GLMs to relate plot-level species richness to dead wood amount and isolation on spatial scales of 20–200 m radius. Further, we used GDMs to determine how dead wood amount and isolation affected beta diversity. Results A larger amount of dead wood increased beetle richness on all spatial scales, while isolation had no effect. For fungi, bryophytes and lichens this was only true on small spatial scales. On larger scales of our study, dead wood amount had no effect, while greater isolation decreased species richness. Further, we found no strong consistent patterns explaining beta diversity. Conclusions Our multi-taxon study shows that habitat amount and isolation can strongly differ in the spatial scale on which they influence local species richness. To generally support the species richness of different saproxylic groups, dead wood must primarily be available in large amounts but should also be evenly distributed because negative effects of isolation already showed at scales under 100 m.

scholarly journals Landscape-Scale Effects of Irrigation on a Dry Cereal Farmland Bird Community

2021 ◽  
Vol 9 ◽  
Author(s):  
David Giralt ◽  
Javiera Pantoja ◽  
Manuel B. Morales ◽  
Juan Traba ◽  
Gerard Bota
Keyword(s):  
Species Richness ◽  
Habitat Fragmentation ◽  
Protected Areas ◽  
Scale Effects ◽  
Spatial Scales ◽  
Bird Community ◽  
Landscape Scale ◽  
Farmland Birds ◽  
Landscape Modification ◽  
Farmland Bird

Landscape modification and habitat fragmentation are one of the major current threats to biodiversity. The main source of habitat fragmentation is the loss of focal habitat area, but changes in the composition of the surrounding landscape also have a direct effect on biodiversity. These changes may lead to the loss of some species but also may favor species replacement. Farmland birds in Europe are affected by landscape changes due to farmland intensification, such as the spread of irrigation, which may occur at different spatial scales. As irrigation is expected to increase in the coming years, which may affect protected areas, it is necessary to evaluate its potential consequences over focal biodiversity. In this study we assess the relationship between the increase of irrigated land at different spatial scales and changes in a dry cereal farmland bird community, bird abundance and species richness, using generalized linear models. We used a dry cereal farmland affinity index to describe the level of community specificity for dry cereal farmland. The increase in irrigated tree orchards produced an increase in species richness up to 500 m away from the irrigated area, which had a negative effect on the dry cereal farmland bird community, by triggering a replacement of specialist by generalist species. Our results show the importance of landscape-scale effects of irrigation occurring outside protected areas on the farmland bird community inside Natura 2000 sites, as well as how these effects are detected even at long distances from the disturbance source.

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