Neutral communities in fragmented landscapes

Habitat fragmentation displays a crucial role in conservation biology. Despite this, little is known about the detailed ecological consequences of habitat fragmentation due to the scarce number of controlled experimental surveys. The species–area relationship, a fundamental concept in ecology, requires the understanding of the fragmentation effects in a long term perspective, which turns this task even harder. Here we address the spatial patterns of species distribution in fragmented landscapes, assuming a neutral community model. We study the species area relationship and how its shape changes as the landscape becomes more fragmented. Recent investigations, based on extensive computer simulation, have contributed to establish some definite conclusions in the study of non‐fragmented landscapes: the existence of a three‐regime or two‐regime scenario for the species–area relationship, the emergence of a power‐law regime at intermediate scales and the augment of the species–area exponent z with the speciation rate. Despite the recent efforts, some other questions remain, such as the dependence of z in the whole range of the speciation rate. Questions like these are currently debated but generalizations cannot be drawn. This is the first paper, to our knowledge, that uses the coalescence method and neutral theory to examine biodiversity on more complex spatial structures. Our simulation results corroborate that the fragmentation plays a crucial role in shaping the species–area relationship, by determining the existence and extension of the power‐law regime associated with small and intermediate areas. On the other hand, when individuals are allowed to disperse over longer distances the species–area relationship now displays the classic triphasic pattern, and the intermediate regime, which is well described by a power‐law, is established even for highly fragmented landscapes.     

Spatial dynamics of Microtus vole populations in continuous and fragmented agricultural landscapes

Small mammal populations often exhibit large-scale spatial synchrony, which is purportedly caused by stochastic weather-related environmental perturbations, predation or dispersal. To elucidate the relative synchronizing effects of environmental perturbations from those of dispersal movements of small mammalian prey or their predators, we investigated the spatial dynamics of Microtus vole populations in two differently structured landscapes which experience similar patterns of weather and climatic conditions. Vole and predator abundances were monitored for three years on 28 agricultural field sites arranged into two 120-km-long transect lines in western Finland. Sites on one transect were interconnected by continuous agricultural farmland (continuous landscape), while sites on the other were isolated from one another to a varying degree by mainly forests (fragmented landscape). Vole populations exhibited large-scale (>120 km) spatial synchrony in fluctuations, which did not differ in degree between the landscapes or decline with increasing distance between trapping sites. However, spatial variation in vole population growth rates was higher in the fragmented than in the continuous landscape. Although vole-eating predators were more numerous in the continuous agricultural landscape than in the fragmented, our results suggest that predators do not exert a great influence on the degree of spatial synchrony of vole population fluctuations, but they may contribute to bringing out-of-phase prey patches towards a regional density level. The spatial dynamics of vole populations were similar in both fragmented and continuous landscapes despite inter-landscape differences in both predator abundance and possibilities of vole dispersal. This implies that the primary source of synchronization lies in a common weather-related environment.     

Contrasting effects of habitat quantity and quality on moth communities in fragmented landscapes

Habitat loss is commonly identified as a major threat to the loss of global biodiversity. In this study, we expand on our previous work by addressing the question of how lepidopteran species richness and composition vary among remnants of North American eastern deciduous forest located within agricultural or pastoral landscapes. Specifically, we tested the relative roles of habitat quantity (measured as stand area and percent forest in the greater landscape) and habitat quality (measured as tree species diversity) as determinants of moth species richness. We sampled >19 000 individuals comprising 493 moth species from 21 forest sites in two forested ecoregions. In the unglaciated Western Allegheny Plateau, the species richness of moths with woody host plants diminished as forest stand size and percent forest in the landscape decreased, but the total species richness and abundance of moths were unaffected by stand size, percent forest in the landscape, or tree species diversity. In contrast, the overall species richness and abundance of moths in the glaciated North Central Tillplain were affected primarily by tree species diversity and secondarily by forest size. Higher tree species diversity may reduce species loss from smaller forest stands, suggesting that small, diverse forests can support comparable numbers of species to those in less diverse, large stands. Smaller forests, however, contained a disproportionate number of moth species that possess larvae known to feed on herbaceous vegetation. Thus, although woody plant feeding moths are lost from forests with changes in stand area, new species appear capable of recolonizing smaller fragments from the surrounding habitat matrix. Our study further suggests that when species replacement occurs, local patch size and habitat quality may be more important than landscape context in determining the community structure of forest Lepidoptera.     

Metapopulation extinction in fragmented landscapes: using bacteria and protozoa communities as model ecosystems

Extinction is notoriously difficult to study because of the long timescales involved and the difficulty in ascertaining that extinction has actually occurred. The effect of habitat subdivision, or fragmentation, on extinction risk is even harder to study, as it requires copious replication of habitat patches on large spatial scales and control of area effects between treatments. I used simple small-scale communities of bacteria and protozoa to study extinction in response to habitat loss and habitat fragmentation. I studied several different community configurations, each with three trophic levels. Unlike most metapopulation studies (experimental as well as theoretical), which have tended to deal with inherently unstable species interactions, I deliberately used community configurations that were persistent in large stock cultures. I recorded the time to extinction of the top predator in single habitat patches of different sizes and in fragmented systems with different degrees of subdivision but the same amount of available habitat. Habitat loss reduced the time to extinction of isolated populations. Fragmented systems went extinct sooner than corresponding unfragmented (continuous) systems of the same overall size. Unfragmented populations persisted longer than fragmented systems (metapopulations) with or without dispersal corridors between subpopulations. In fact, fragmented systems where the fragments were linked by dispersal corridors went extinctly significantly sooner than those where subpopulations were completely isolated from each other. If these results extend to more "natural" systems, it suggests a need for caution in management programs that emphasize widespread establishment of wildlife corridors in fragmented landscapes.     

Managing rock outcrops to improve biodiversity conservation in Australian agricultural landscapes

Summary  Rocky outcrops are prominent geological features in agricultural landscapes worldwide. Reptiles are a major component of these habitats and some species are restricted to, and more abundant on, rocky outcrops than in remnant vegetation. Rock outcrops are important to reptiles because they provide resources that are often limited in the surrounding landscape (e.g. micro-gradients in climatic conditions, basking- and retreat-sites). However, there is a knowledge gap in the literature addressing the conservation value of small, rocky outcrops. Management may be necessary to reverse habitat degradation in these systems. We identify four key areas of management that need to be addressed to improve outcrop habitat values and enhance biodiversity conservation in agricultural landscapes. Specific actions involve: (i) protecting outcrops from processes that cause damage to rock microhabitat, (ii) monitoring and managing changes in vegetation structure to maintain thermally suitable environments, (iii) applying integrated pest animal control and (iv) improving matrix management to enhance inselberg function and landscape connectivity. Further research is required to evaluate the efficacy of different management regimes on outcrop biota. We hope this paper will provide the stimulus for land managers to incorporate rocky outcrops in future biodiversity conservation programmes.     

Biodiversity in agricultural landscapes: different non-crop habitats increase diversity of ground-dwelling beetles (Coleoptera) but support different communities

Agricultural intensification poses a major threat to the conservation of biodiversity and associated ecosystem services. Since non-crop habitats are regarded as important refuges for farmland biodiversity, various greening measures have been proposed to halt biodiversity loss. However, the effectiveness of these measures for biodiversity conservation is still under debate. Therefore, we here compared ground-dwelling beetle (Coleoptera) assemblages of different non-crop habitats (field margins, set-aside fields sown with wildflowers, and permanent grassland fallows) and wheat fields within an intensively used agricultural landscape in western Germany. Taxonomic diversity of Carabidae, Staphylinidae and other coleopteran families and their conservation value were higher in all non-crop habitats than on wheat fields. Surprisingly, though, different types of non-crop habitats did not differ in species richness or the number of threatened species. Thus, field margins and sown wildflower fields were as effective in promoting beetle diversity as grassland fallows. However, different non-crop habitats supported different species assemblages, and several species, in particular especially large ones, were restricted to grassland fallows. These results suggest that different greening measures are effective in promoting the biodiversity of beetles, and that permanent grassland fallows are essential for nature conservation. The fact that habitat types harbored different assemblages stresses the need to combine a variety of greening measures to yield the highest benefit for biodiversity.

     

Variation in plant species richness in and adjacent to 64 ponds in SE Norwegian agricultural landscapes

All vascular plants, classified by life and growth form into six groups, four groups of hydrophytes (lemnids, nymphaeids, elodeids and isoetids), helophytes, and terrestrial species of pond margins, were inventoried in 64 SE Norwegian agricultural landscape ponds and their adjacent margins. The study sites varied considerably with respect to species richness; 0–4 for each hydrophyte group, 0–9 for helophytes, and 13–77 for terrestrial species. A total of 56 explanatory variables were recorded for each pond and adjacent margin to explain the observed richness variability.     

Variation in plant species composition in and adjacent to 64 ponds in SE Norwegian agricultural landscapes

All vascular plants, classified by life and growth form into aquatic species (hydrophytes and helophytes) and terrestrial species of pond margins, were inventoried in 64 SE Norwegian agricultural landscape ponds and their adjacent margins for which also 56 explanatory variables were recorded. Gradients in species composition, found separately for aquatic and terrestrial species by parallel DCA and GNMDS ordinations, were interpreted by correlation and geostatistical analyses.     

Biodiversity in agricultural landscapes: the ground beetle communities of woody uncultivated habitats

Agricultural landscapes can be defined as mosaics of landscape elements which are affected by farming practices. Woodland habitats, even though they are managed, are amongst the most stable elements of agricultural landscapes and can play a key role in the maintenance of biodiversity. This study of the ground beetle (carabid) communities of woodlands and woody linear features in a Scottish agricultural landscape shows that these habitats contribute significantly to the overall landscape diversity of these beetles. Communities in woods and hedgerows display the same species diversity and are both characterized by the presence of forest species. The main factors constraining carabid communities in both environments are the grazing intensity and, to a lesser extent, the type of soil. Heavily grazed locations are characterized by the occurrence of grassland species while forest species are restricted to ungrazed locations. At the landscape scale, the distribution of the forest species is limited by spatial isolation, indicating that there are insufficient functional links between woodland habitats in the study area. Isolation could be compensated for either by a better control of grazing so that linear features can be used as dispersal corridors for forest carabids or by planting more linear features and woods in the area.     

Simulating direct and indirect effects of climatic changes on rare perennial plant species in fragmented landscapes

Question: How does climate change influence plant species population dynamics, their time to extinction, and proportion of occupied habitats in a fragmented landscape? Location: Germany and Central European lowland. Methods: We apply a mechanistic general simulation model to test the response of plant functional types to direct and indirect effects of climate change. Three functional types were chosen to represent a set of well‐studied perennial plant species: Juncus atratus, Gentiana pneumonanthe and Primula veris. We link local population dynamics within a heterogeneous, fragmented landscape context. “Species spheres”, i.e. multi‐dimensional parameter ranges rather than single parameter realizations, based on field and literature data served as proxy for life stage transition parameters. Four climatic scenarios summarizing different cumulative weather effects on demographic rates and different local disturbance frequencies were run. The model predicts “time to extinction” (TE) and “proportion of occupied habitat” (POH) as regional indicators for species extinction risk. Results: TE decreased for all species when weather conditions worsened, and even more so when the frequency of local destructive events additionally increased. However, management towards fewer disturbance events could buffer the negative effect of climate to some extent. The magnitude of these responses varied with species type. POH declined with an increase in bad weather as well as with increasing disturbance frequency. The better the climatic conditions, the less severe were disturbances on population performance. Conclusions: The “species spheres” proved to be a valuable approach for predictive trends. As climate change usually also implies destructive events such as land‐use change, flooding or fire, our model on local and regional extinction risks can support conservation issues and management actions.     

Bird assemblages in fragmented agricultural landscapes: the role of small brigalow remnants and adjoining land uses

Agricultural intensification typically leads to changes in bird diversity and community composition, with fewer species and foraging guilds present in more intensively managed parts of the landscape. In this study, we compare bird communities in small (2–32 ha) brigalow (Acacia harpophylla) remnants with those in adjacent uncultivated grassland, previously cultivated grassland and current cropland, to determine the contribution of different land uses to bird diversity in the agricultural landscape. Twenty remnant brigalow patches and adjacent agricultural (‘matrix’) areas in southern inland Queensland, Australia were sampled for bird composition and habitat characteristics. The richness, abundance and diversity of birds were all significantly higher in brigalow remnants than in the adjacent matrix of cropping and grassland. Within the matrix, species richness and diversity were higher in uncultivated grasslands than in current cultivation or previously cultivated grasslands. Forty-four percent of bird species were recorded only in brigalow remnants and 78% of species were recorded in brigalow and at least one other land management category. Despite high levels of landscape fragmentation and modification, small patches of remnant brigalow vegetation provide important habitat for a unique and diverse assemblage of native birds. The less intensively managed components of the agricultural matrix also support diverse bird assemblages and thus, may be important for local and regional biodiversity conservation.     

Sedimentary Factors are Key Predictors of Carbon Storage in SE Australian Saltmarshes

Although coastal vegetated ecosystems are widely recognised as important sites of long-term carbon (C) storage, substantial spatial variability exists in quantifications of these ‘blue C’ stocks. To better understand the factors behind this variability we investigate the relative importance of geomorphic and vegetation attributes to variability in the belowground C stocks of saltmarshes in New South Wales (NSW), southeast Australia. Based on the analysis of over 140 sediment cores, we report mean C stocks in the surface metre of sediments (mean ± SE = 164.45 ± 8.74 Mg C ha^?1) comparable to global datasets. Depth-integrated stocks (0–100 cm) were more than two times higher in fluvial (226.09 ± 12.37 Mg C ha^?1) relative to marine (104.54 ± 7.11) geomorphic sites, but did not vary overall between rush and non-rush vegetation structures. More specifically, sediment grain size was a key predictor of C density, which we attribute to the enhanced C preservation capacity of fine sediments and/or the input of stable allochthonous C to predominantly fine-grained, fluvial sites. Although C density decreased significantly with sediment depth in both geomorphic settings, the importance of deep C varied substantially between study sites. Despite modest spatial coverage, NSW saltmarshes currently hold approximately 1.2 million tonnes of C in the surface metre of sediment, although more C may have been returned to the atmosphere through habitat loss over the past approximately 200 years. Our findings highlight the suitability of using sedimentary classification to predict blue C hotspots for targeted conservation and management activities to reverse this trend.     

Understory bird communities in Amazonian rainforest fragments: species turnover through 25 years post-isolation in recovering landscapes

Inferences about species loss following habitat conversion are typically drawn from short-term surveys, which cannot reconstruct long-term temporal dynamics of extinction and colonization. A long-term view can be critical, however, to determine the stability of communities within fragments. Likewise, landscape dynamics must be considered, as second growth structure and overall forest cover contribute to processes in fragments. Here we examine bird communities in 11 Amazonian rainforest fragments of 1-100 ha, beginning before the fragments were isolated in the 1980s, and continuing through 2007. Using a method that accounts for imperfect detection, we estimated extinction and colonization based on standardized mist-net surveys within discreet time intervals (1-2 preisolation samples and 4-5 post-isolation samples). Between preisolation and 2007, all fragments lost species in an area-dependent fashion, with loss of as few as <10% of preisolation species from 100-ha fragments, but up to 70% in 1-ha fragments. Analysis of individual time intervals revealed that the 2007 result was not due to gradual species loss beginning at isolation; both extinction and colonization occurred in every time interval. In the last two samples, 2000 and 2007, extinction and colonization were approximately balanced. Further, 97 of 101 species netted before isolation were detected in at least one fragment in 2007. Although a small subset of species is extremely vulnerable to fragmentation, and predictably goes extinct in fragments, developing second growth in the matrix around fragments encourages recolonization in our landscapes. Species richness in these fragments now reflects local turnover, not long-term attrition of species. We expect that similar processes could be operating in other fragmented systems that show unexpectedly low extinction.     

The culture of bird conservation: Australian stakeholder values regarding iconic,flagship and rare birds

Iconic, flagship and rare threatened bird taxa attract disproportionate amounts of public attention, and are often used to enable broader conservation strategies. Yet, little is known about why certain taxa achieve iconic or flagship status. Also unclear is whether the perception of rarity among those acting to conserve threatened birds is sufficient to influence attitudes and behaviour that lead to effective conservation action and, if so, which characteristics of rare birds are important to their conservation. We interviewed 74 threatened bird conservation stakeholders to explore perceptions about iconic, flagship and rare threatened birds and classified their attitudes using a new typology of avifaunal attitudes. There was a relationship between societal interest and conservation effort for threatened species characterised as iconic, flagship and rare. Iconic species tended to arouse interest or emotion in people due to being appealing and readily encountered, thereby attracting conservation interest that can benefit other biodiversity. Flagships tended to have distinguishing physical or cultural characteristics and were used to convey conservation messages about associated biodiversity. Attitudes about rarity mostly related to a taxon’s threatened status and small population size. Rarity was important for threatened bird conservation but not always associated with attitudes and behaviour that lead to effective conservation action. We conclude that conservation action for individual threatened bird taxa is biased and directly influenced by the ways taxa are socially constructed by stakeholders, which is specific to prevailing culture and stakeholder knowledge.     

Silene rothmaleri P. Silva (Caryophyllaceae), a rare, fragmented but genetically diverse species

Silene rothmaleri is an endemic Portuguese species considered extinct until 1992, when it was rediscovered in the wild with a highly fragmented distribution. These rare plants occur along the southwestern Portuguese coast in small populations, which in addition to phenological differences that occur along the north–south gradient could create a pattern of genetic isolation. To evaluate the degree of genetic diversity and estimate the relationship between population fragmentation and genetic variability, we analysed the five known populations of S. rothmaleri using random amplified polymorphic DNA. Degree of polymorphism and Shannon Index of phenotypic diversity revealed high levels of diversity, found mainly within populations. PCo and cluster analysis revealed a distinct north–south cline, which was confirmed by spatial autocorrelation (Mantel) analysis. This indicates the existence of gene flow between small nearby populations and its insufficiency between widely separated populations. Levels of gene flow (Nm) estimated from the Shannon Index reveal a pattern consistent with a larger past distribution that went through a period of contraction and lack of gene flow followed by population differentiation. The central and largest population probably acts as a core of genetic variability inherited as a relict from a larger and more diverse ancestral population.     

Genetic variation and plant performance in fragmented populations of globeflowers (Trolliuseuropaeus) within agricultural landscapes

The management of remnant populations in highly fragmented landscapes requires a thorough understanding of the processes shaping population persistence. We investigated relationships between population characteristics (i.e. size, density and pollinator abundance), offspring performance, genetic diversity and differentiation in Trollius europaeus, a plant with a nursery pollination system. In 19 populations of different sizes and located in north-east Switzerland, an area which has undergone widespread land use changes over the last decades, we assessed neutral genetic diversity (N _total = 383) using AFLPs and plant performance in a greenhouse experiment (N _total = 584) using competition and control treatments. Overall genetic differentiation was low (F _ST = 0.033) with a marginal significant isolation by distance effect (P = 0.06) indicating (historical) genetic connectivity among the populations. Mean expected heterozygosity was H _E of 0.309 (0.0257–0.393) while inbreeding coefficients (F _IS) were significant in only three populations. Genetic diversity was not related to population size, plant density or pollinator abundance. Plant performance was reduced under competition (P < 0.001) but the severity of competition was independent of genetic diversity and population size. In summary, remnant populations of T. europaeus retain genetic diversity and seem capable of persisting under the present conditions within an agricultural matrix. T. europaeus is a perennial herb, thus it may require several generations for the negative effects of fragmentation and isolation to manifest. Our findings indicate that small populations are as important as large populations for the conservation and management of genetic resources.