Context

The habitat amount hypothesis has rarely been tested on plant communities. It remains unclear how habitat amount affect species richness in habitat fragments compared to island effects such as isolation and patch size.

Objectives

How do patch size and spatial distribution compared to habitat amount predict plant species richness and grassland specialist plant species in small grassland remnants? How does sampling area affect the prediction of spatial variables on species richness?

Methods

We recorded plant species density and richness on 131 midfield islets (small remnants of semi-natural grassland) situated in 27 landscapes in Sweden. Further, we tested how habitat amount, compared to focal patch size and distance to nearest neighbor predicted species density and richness of plants and of grassland specialists.

Results

A total of 381 plant species were recorded (including 85 grassland specialist species). A combination of patch size and isolation was better in predicting both density and richness of species compared to habitat amount. Almost 45% of species richness and 23% of specialist species were explained by island biogeography parameters compared to 19 and 11% by the amount of habitat. A scaled sampling method increased the explanation level of island biogeography parameters and habitat amount.

Conclusions

Habitat amount as a concept is not as good as island biogeography to predict species richness in small habitats. Priority in landscape planning should be on larger patches rather than several small, even if they are close together. We recommend a sampling area scaled to patch size in small habitats.

Context

The ecological literature is filled with studies highlighting the importance of both habitat loss and fragmentation on biodiversity. The patch concept has been central to these findings, being also at the heart of many ecological theories. Recently, the habitat amount hypothesis has been proposed as an alternative, where the patch concept is put to a rest, and both patch size and patch isolation effects on species richness are reduced to a single gradient: habitat loss in the landscape.

Objectives

As this theory stated clear predictions that could be experimentally tested, many formal tests of the hypothesis have been published recently and this study aims at synthesizing their results.

Methods

A meta-analysis of 13 tests of the habitat amount hypothesis was conducted, to produce a single combined test of the theory.

Results

The 13 tests combined suggest that effects of patch size and isolation, while controlling for habitat amounts, do exist although their overall effect is weak (r?=?0.158).

Conclusions

Literal interpretations of the habitat amount hypothesis, where patch size and isolation have absolutely no effect on species richness, are probably oversimplifications of the processes at work. Still, the theory could prove useful as a baseline of the effects of habitat loss, against which patch size and isolation effects must be contrasted.

Context

The classical theory of island biogeography explains loss of species in fragmented landscapes as an effect of remnant patch size and isolation. Recently this has been challenged by the habitat amount and habitat continuum hypotheses, according to which persistence in modified landscapes is related to total habitat amount rather than habitat configuration or the ability of species to use all habitats to varying degrees. Distinguishing between these theories is essential for effective conservation planning in modified landscapes.

Objective

Identify which factors of habitat type, amount and configuration predict the persistence of a keystone woodland specialist, the eastern bettong Bettongia gaimardi, in a fragmented landscape.

Method

In the Midlands region of Tasmania we carried out camera surveys at 62 sites in summer and winter. We included habitat and landscape features to model whether habitat amount or patch size and isolation influenced the presence of the eastern bettong, and to measure effects of habitat quality.

Results

Habitat amount within a 1 km buffer was a better predictor of occupancy than patch size and isolation. Occupancy was also affected by habitat quality, indicated by density of regenerating stems.

Conclusion

Our results support the habitat amount hypothesis as a better predictor of presence. For a species that is able to cross the matrix between remnant patches and utilise multiple patches, the island biogeography concept does not explain habitat use in fragmented landscapes. Our results emphasize the value of small remnant patches for conservation of the eastern bettong, provided those patches are in good condition.

Context

According to the trophic-rank hypothesis, species may be differentially affected by habitat isolation due to their trophic position in the food chain, i.e. high-order trophic levels may be more negatively affected than low-order levels.

Objectives

The aim of this paper is to study how species richness, abundance and composition of saproxylic beetle communities are affected by patch (=tree) quality and small-scale patch connectivity. Following the trophic-rank hypothesis, we expected predators to be more negatively affected by patch isolation than wood-feeding beetles.

Methods

We studied the beetle community, patch connectivity and patch quality on 28 large oaks. Different connectivity measures were calculated using 50 m-buffers around trees and using distances to the five nearest trees.

Results

Beetle species richness increased with the diameter of oaks, i.e. patch quality. No evidence of the trophic-rank hypothesis was found for species richness patterns. In accordance with the trophic-rank hypothesis, abundance of predatory beetles increased with patch connectivity but lower trophic levels were unaffected or even decreased with patch connectivity.

Conclusions

The structure of invertebrate communities on trees changes with small-scale patch connectivity due to a differential response of low-order and high-order trophic levels. Isolated trees are more exposed to the sun than the more connected trees, which may affect the beetles; however, it was impossible to distinguish the microclimatic from the spatial effects. Although scattered trees generally have a higher conservation value than trees in forests, we conclude that forest trees may be more important for certain trophic levels.

Context

Species show different sensitivity to habitat loss and fragmentation depending on their specialization. Populations of a species at the range margin are generally assumed to be more stenoecious than populations at the core of the distribution and should therefore be more sensitive to habitat fragmentation.

Objectives

We evaluated the hypothesis that fragmentation effects species more strongly at the range periphery of their range compared to the core, resulting in lower genetic variability in comparable patch sizes and lower gene flow among populations.

Methods

We compared the genetic diversity and structure of five sand lizard (Lacerta agilis) populations at the margin of its range in Bulgaria and of 11 populations at the core of its distribution in Germany. We based the analysis on microsatellites, comprising 15 loci in Bulgaria and 12 in Germany.

Results

All diversity indices declined with patch size. For medium-sized patches all diversity indices were lower at the range periphery compared to the core, with two of them being significant. AIC_c based model selection showed strong support for core/periphery and patch size effects for observed and expected heterozygosity but only a patch size effect for allelic richness. There was no isolation-by-distance and each sampled population was allocated to a separate cluster with high probability for both countries, indicating that all populations are (almost) completely isolated.

Conclusion

Our study indicates an increased sensitivity of a species to fragmentation at the periphery compared to the core of its distribution. This differential sensitivity should be accounted for when prioritizing species based on their fragmentation sensitivity in landscape management.

Context

Habitat loss is a major threat to biodiversity. It can create temporal lags in decline of species in relation to destruction of habitat coverage. Plant species specialized in semi-natural grasslands, especially meadows, often express such extinction debt.

Objectives

We studied habitat loss and fragmentation of meadows and examined whether the changes in meadow coverage had caused an extinction debt on vascular plants. We also studied whether historical or present landscape patterns or contemporary environmental factors were more important determinants of species occurrence.

Methods

We surveyed the plant species assemblages of 12 grazed and 12 mown meadows in Central Finland and detected the meadow coverages from their surroundings on two spatial scales and on three time steps. We modelled the effects of functional connectivity, habitat amount, and isolation on species richness and community composition.

Results

We observed drastic and dynamic meadow loss in landscapes surrounding our study sites during the last 150 years. However, we did not find explicit evidence for an extinction debt in meadow plants. The observed species richness correlated with contemporary factors, whereas both contemporary factors and habitat availability during the 1960s affected community composition.

Conclusions

Effective conservation management of meadow biodiversity builds on accurate understanding of the relative importance of past and present factors on species assemblages. Both mown and grazed meadows with high species richness need to be managed in the future. The management effort should preferably be targeted to sites located near to each other.

Context

Habitat loss and habitat fragmentation negatively affect amphibian populations. Roads impact amphibian species through barrier effects and traffic mortality. The landscape variable ‘accessible habitat’ considers the combined effects of habitat loss and roads on populations.

Objectives

The aim was to test whether accessible habitat was a better predictor of amphibian species richness than separate measures of road effects and habitat loss. I assessed how accessible habitat and local habitat variables determine species richness and community composition.

Methods

Frog and tadpole surveys were conducted at 52 wetlands in a peri-urban area of eastern Australia. Accessible habitat was delineated using a highway. Regressions were used to examine relationships between species richness and eleven landscape and local habitat variables. Redundancy analysis was used to examine relationships between community composition and accessible habitat and local habitat variables.

Results

Best-ranked models of species richness included both landscape and local habitat variables. There were positive relationships between species richness and accessible habitat and distance to the highway, and uncertain relationships with proportion cover of native vegetation and road density. There were negative relationships between species richness and concreted wetlands and wetland electrical conductivity. Four species were positively associated with accessible habitat, whereas all species were negatively associated with wetland type.

Conclusions

Barrier effects caused by the highway and habitat loss have negatively affected the amphibian community. Local habitat variables had strong relationships with species richness and community composition, highlighting the importance of both availability and quality of habitat for amphibian conservation near major roads.

Context

Hoverflies are often used as bio-indicators for ecosystem conservation, but only few studies have actually investigated the key factors explaining their richness in woodlands.

Objectives

In a fragmented landscape in southwest France, we investigated the joint effects of woodland area, structural heterogeneity, connectivity and history on the species richness of forest-specialist hoverflies, and whether there was a time lag in the response of hoverflies to habitat changes, and tested the effect of spatiotemporal changes.

Methods

Current species richness was sampled in 48 woodlands using 99 Malaise traps. Structural variables were derived from a rapid habitat assessment protocol. Old maps and aerial photographs were used to extract past and present spatial patterns of the woodlands since 1850. Relationships between species richness and explanatory variables were explored using generalized linear models.

Results

We show that current habitat area, connectivity, historical continuity and the average density of tree-microhabitats explained 35 % of variation in species richness. Species richness was affected differently by changes in patch area between 1979 and 2010, depending on woodland connectivity. In isolated woodlands, extinction debt and colonization credit were revealed, showing that even several decades are not sufficient for hoverflies to adapt to landscape-scale habitat conditions.

Conclusions

These findings emphasise the importance of maintaining connectedness between woodlands, which facilitates the dispersion in a changing landscape. Our results also highlight the benefits of using a change-oriented approach to explain the current distribution patterns of species, especially when several spatial processes act jointly.

Context

Landscape and habitat filters are major drivers of biodiversity of small habitat islands by influencing dispersal and extinction events in plant metapopulations.

Objectives

We assessed the effects of landscape and habitat filters on the species richness, abundance and trait composition of grassland specialist and generalist plants in small habitat islands. We studied traits related to functional spatial connectivity (dispersal ability by wind and animals) and temporal connectivity (clonality and seed bank persistence) using model selection.

Methods

We sampled herbaceous plants, landscape (local and regional isolation) and habitat filters (inclination, woody encroachment and disturbance) in 82 grassland islands in Hungary.

Results

Isolation decreased the abundance of good disperser specialist plants due to the lack of directional vectors transferring seeds between suitable habitat patches. Clonality was an effective strategy, but persistent seed bank did not support the survival of specialist plants in isolated habitats. Generalist plants were unaffected by landscape filters due to their wide habitat breadth and high propagule availability. Clonal specialist plants could cope with increasing woody encroachment due to their high resistance against environmental changes; however, they could not cope with intensive disturbance. Steep slopes providing environmental heterogeneity had an overall positive effect on species richness.

Conclusions

Specialist plants were influenced by the interplay of landscape filters influencing their abundance and habitat filters affecting species richness. Landscape filtering by isolation influenced the abundance of specialist plants by regulating seed dispersal. Habitat filters sorted species that could establish and persist at a site by influencing microsite availability and quality.

Context

Identifying the drivers shaping biological assemblages in fragmented tropical landscapes is critical for designing effective conservation strategies. It is still unclear, however, whether tropical biodiversity is more strongly affected by forest loss, by its spatial configuration or by matrix composition across different spatial scales.

Objectives

Assessing the relative influence of forest patch and landscape attributes on dung beetle assemblages in the fragmented Lacandona rainforest, Mexico.

Methods

Using a multimodel inference approach we tested the relative impact of forest patch size and landscape forest cover (measures of forest amount at the patch and landscape scales, respectively), patch shape and isolation (forest configuration indices at the patch scale), forest fragmentation (forest configuration index at the landscape scale), and matrix composition on the diversity, abundance and biomass of dung beetles.

Results

Patch size, landscape forest cover and matrix composition were the best predictors of dung beetle assemblages. Species richness, beetle abundance, and biomass decreased in smaller patches surrounded by a lower percentage of forest cover, and in landscapes dominated by open-area matrices. Community evenness also increased under these conditions due to the loss of rare species.

Conclusions

Forest loss at the patch and landscape levels and matrix composition show a larger impact on dung beetles than forest spatial configuration. To preserve dung beetle assemblages, and their key functional roles in the ecosystem, conservation initiatives should prioritize a reduction in deforestation and an increase in the heterogeneity of the matrix surrounding forest remnants.

Context

Although small isolated habitat patches may not be able to maintain a minimum viable population, small patches that are structurally isolated may be functionally connected if individuals can cross the gaps between them, in which case, their areas could be added to form a larger habitat patch, eventually surpassing the size threshold for holding a viable population.

Objectives

We studied whether models based on the size and isolation of habitat patches could be used to predict the distribution of the Chestnut-throated Huet-Huet (Pteroptochos castaneus) in fragmented landscapes of the coastal range of the Maule region, central Chile.

Methods

We selected seven 10,000-ha landscapes (8.4–70.7% forest cover). For each habitat patch we made 18 predictions of the presence of the species based on the combination of two thresholds: three critical patch sizes for maintaining a viable population (62.5, 125 and 250 ha) and six critical isolation distances between patches (0, 10, 50, 100, 150 and 200 m). We used playbacks in 59 sampling points to estimate the species’ presence/absence. We used logistic regressions to test whether the output of the patch-matrix models could explain part of the variation in the presence of Pteroptochos castaneus.

Results

The best predictions for the presence of P. castaneus were obtained with the most conservative scenarios (125–250 ha to 0–10 m), including a positive effect of the understory cover and a lack of effect of the forest type (native or exotic).

Conclusions

Our findings suggest that the long term persistence of P. castaneus may depend on the existence of large and/or very connected forest tracts.

Context

Urbanization has altered many landscapes around the world and created novel contexts and interactions, such as the rural–urban interface.

Objectives

We sought to address how a forest patch’s location in the rural–urban interface influences which avian species choose to occur within the patch. We predicted a negative relationship between forest bird richness and urbanization surrounding the patch, but that it would be ameliorated by the area of tree cover in the patch and matrix, and that total tree-cover area would be more influential on forest bird species richness than area of tree cover in the focal patch alone.

Methods

We conducted bird surveys in 44 forest patches over 2 years in Southeast Michigan and evaluated bird presence and richness relative to patch and matrix tree cover and development density.

Results

We observed 43 species, comprised of 21 Neotropical migrants, 19 residents, and three short-distance migrants. Focal-patch tree-cover area and the matrix tree-cover area were the predominant contributors to a site’s overall forest-bird species richness at the rural–urban interface, but the addition of percent of over-story vegetation and percentage of deciduous tree cover influenced the ability of the patches to support forest species, especially Neotropical migrants. Development intensity in the matrix was unrelated to species richness and only had an effect in four species models.

Conclusions

Although small forest patches remain an important conservation strategy in developed environments, the influence of matrix tree cover suggests that landscape design decisions in surrounding matrix can contribute conservation value at the rural–urban interface.

Context

Loss and fragmentation of semi-natural grasslands has critically affected many butterfly species in Europe. Habitat area and isolation can have strong effects on the local biodiversity but species may also be strongly affected by the surrounding matrix.

Objectives

We explored how different land cover types in the landscape explained the occurrence of butterfly species in semi-natural grasslands.

Methods

Using data from 476 semi-natural grasslands in Sweden, we analysed the effect of matrix composition on species richness and occurrence. Additionally, we analysed at which spatial scales butterflies responded to matrix types (forests, semi-natural grasslands, arable land and water).

Results

Forest cover showed the strongest positive effect on species richness, followed by semi-natural grasslands. Forest also had a positive effect on red-listed species at local scales. Responses to matrix composition were highly species-specific. The majority of the 30 most common species showed strong positive responses to the amount of forest cover within 200–500 m. There was a smaller group of species showing a positive response to arable land cover within 500–2000 m. Thirteen species showed positive responses to the amount of semi-natural grasslands, generally at larger scales (10–30 km).

Conclusions

Our study showed that surrounding forest is beneficial for many grassland butterfly species and that forests might mitigate the negative effects of habitat loss caused by agricultural intensification. Also, semi-natural grasslands were an important factor for species richness at larger spatial scales, indicating that a landscape consisting mainly of supporting habitats (i.e. forests) are insufficient to sustain a rich butterfly fauna.

Context

Urban environments create a wide range of habitats that harbour a great diversity of plant species, many of which are of alien origin. For future urban planning and management of the green areas within the city, understanding of the spatial distribution of invasive alien species is of great importance.

Objectives

Our main aim was to assess how availability of different ecosystem types within a city area, as well as several parameters describing urban structure interact in determining the cover and identity of invasive alien species.

Methods

We studied the distribution of chosen invasive plant species in a mid-sized city in the Czech Republic, central Europe, on a gradient of equal sized cells from the city centre to its outskirts.

Results

A great amount of variation was explained by spatial predictors but not shared with any measured variables. The species cover of invasive species decreased with increasing proportion of urban greenery and distance from the city centre, but increased with habitat richness; road margins, ruderal sites, and railway sites were richest in invasive species. In contrast, the total number of invasive species in cells significantly decreased with increasing distance from the city centre, but increased with habitat richness.

Conclusions

Our results suggest that different invasive species prefer habitats in the vicinity of the city centre and at its periphery and the spatial structure and habitat quality of the urban landscape needs to be taken into account, in efforts to manage alien plant species invasions in urban environments.

Context

The relative influence of habitat loss versus configuration on avian biodiversity is poorly understood. However, this knowledge is essential for developing effective land use strategies, especially for grassland songbirds, which have experienced widespread declines due to land use changes. Habitat configuration may be particularly important to grassland songbirds as configuration of habitat affects the extent of edge effects on the landscape, which strongly influences habitat use by grassland birds.

Objectives

We examined the relative influence of grassland amount and a measure of grassland configuration per se (Landscape Shape Index; LSI) on the relative abundance and richness of grassland songbirds.

Methods

In 2013, 361 avian point counts were conducted across 47, 2.4 km radii landscapes in south-west Manitoba, Canada, selected to minimize the correlation between grassland amount and configuration. We used generalized linear mixed-effects models within a multi-model inference framework to determine the relative importance of grassland amount and configuration on songbird response variables.

Results

Effects of grassland amount and configuration were generally weak, but effects of configuration were greater than grassland amount for most species. Relative abundance and richness of obligate species, and Savannah sparrows, showed a strong negative response to LSI, while grasshopper sparrows responded positively to grassland amount.

Conclusion

Our results suggest that habitat configuration must be considered when managing landscapes for conservation of grassland songbirds. Maintaining large, intact tracts of grasslands and limiting development of roads that bisect grassland parcels may be an effective means of maintaining grassland songbird diversity and abundance in northern mixed-grass prairies.

Context

Understanding how landscape patterns affect species diversity is of great importance in the fields of biogeography, landscape ecology and conservation planning, but despite the rapid advance in biodiversity analysis, investigations of spatial effects on biodiversity are still largely focused on species richness.

Objectives

We wanted to know if and how species richness and species composition are differentially driven by the spatial measures dominating studies in landscape ecology and biogeography. As both measures require the same limited presence/absence information, it is important to choose an appropriate diversity measure, as differing results could have important consequences for interpreting ecological processes.

Methods

We recorded plant occurrences on 112 islands in the Baltic archipelago. Species richness and composition were calculated for each island, and the explanatory power of island area and habitat heterogeneity, distance to mainland and structural connectivity at three different landscape sizes were examined.

Results

A total of 354 different plant species were recorded. The influence of landscape variables differed depending on which diversity measure was used. Island area and structural connectivity determined plant species richness, while species composition revealed a more complex pattern, being influenced by island area, habitat heterogeneity and structural connectivity.

Conclusions

Although both measures require the same basic input data, species composition can reveal more about the ecological processes affecting plant communities in fragmented landscapes than species richness alone. Therefore, we recommend that species community composition should be used as an additional standard measure of diversity for biogeography, landscape ecology and conservation planning.

Context

The anthropocene is characterised by global landscape modification, and the structure of remnant habitats can explain different patterns of species richness. The most pervasive processes of degradation include habitat loss and fragmentation. However, a recovery of modified landscape is occurring in some areas.

Objectives

The main goal is to know how lichen and bryophyte epiphytic richness growing on Mediterranean forests is influenced not only by fragments characteristics but also by the structure of the landscape. We introduce a temporal dimension in order to evaluate if the historical landscape structure is relevant for current epiphytic communities.

Methods

40 well-preserved forest fragments were selected in a landscape with a large habitat loss over decades, but with a recovery of forest surface in the last 55 years. The most relevant fragment and landscape-scale attributes were considered. Some of the variables were measured in three different years to incorporate a temporal framework.

Results

The results showed that variables at fragment scale had a higher influence, whereas variables at the landscape scale were irrelevant. Among all the historical variables analyzed, only the shift in forest fragment size had influence on species richness.

Conclusions

Mediterranean forests had suffered fragmentation along centuries. Their epiphytic communities also suffer the hard conditions of Mediterranean climate. Our results indicate that Mediterranean epiphytic communities may be in a threshold since it they will never be similar to those communities existing previous fragmentation process even a recovery habitat occur or, they may require more time to response to this habitat recovery.

Context

The relative importance of habitat area and connectivity for species richness is often unknown. Connectivity effects may be confounded with area effects or they may be of minor importance as posited by the habitat-amount hypothesis.

Objectives

We studied effects of habitat area and connectivity of linear landscape elements for plant species richness at plot level. We hypothesized that connectivity of linear landscape elements, assessed by resistance distance, has a positive effect on species richness beyond the effect of area and, further, that the relative importance of connectivity varies among groups of species with different habitat preferences and dispersal syndromes.

Methods

We surveyed plant species richness in 50 plots (25 m²) located on open linear landscape elements (field margins, ditches) in eight study areas of 1 km² in agricultural landscapes of Northwest Germany. We calculated the area of linear landscape elements and assessed their connectivity using resistance distance within circular buffers (500 m) around the plots. Effects of area and connectivity on species richness were modelled with generalised linear mixed models.

Results

Species richness did not increase with area. Resistance distance had significant negative effects on total richness and on the richness of typical species of grasslands and wetlands. Regarding dispersal syndromes, resistance distance had negative effects on the richness of species with short-distance, long-distance and aquatic dispersal. The significant effects of resistance distance indicated that species richness increased with connectivity of the network of linear landscape elements.

Conclusions

Connectivity is more important for plant species richness in linear landscape elements than area. In particular, the richness of plant species that are dispersal limited and confined to semi-natural habitats benefits from connective networks of linear landscape elements in agricultural landscapes.

Context

Habitat destruction is the leading threat to terrestrial biodiversity, isolating remnant habitat in a matrix of modified vegetation.

Objectives

Our goal was to determine how species richness in several broad taxonomic groups from remnant forest was influenced by matrix quality, which we characterized by comparing plant biomass in forest and the surrounding matrix.

Methods

We coupled data on species-area relationships (SARs) in forest remnants from 45 previously published studies with an index of matrix quality calculated using new estimates of plant biomass derived from satellite imagery.

Results

The effect size of SARs was greatest in landscapes with low matrix quality and little forest cover. SARs were generally stronger for volant than for non-volant species. For the terrestrial taxa included in our analysis, matrix quality decreased as the proportion of water, ice, or urbanization in a landscape increased.

Conclusions

We clearly demonstrate that matrix quality plays a major role in determining patterns of species richness in remnant forest. A key implication of our work is that activities that increase matrix quality, such as active and passive habitat restoration, may be important conservation measure for maintaining and restoring biodiversity in modified landscapes.