A multi-taxa assessment of nestedness patterns across a multiple-use Amazonian forest landscape

Understanding how biodiversity is partitioned among alternative land-uses is an important first step for developing effective conservation plans in multiple-use landscapes. Here, we analysed nestedness patterns of species composition for nine different taxonomic groups [dung beetles, fruit-feeding butterflies, orchid bees, scavenger flies, leaf-litter amphibians, lizards, bats, birds and woody plants (trees and lianas)] in a multiple-use forestry landscape in the Brazilian Amazon containing primary, secondary and Eucalyptus plantation forests. A formal nestedness analysis was performed to investigate whether species-poor land-uses were comprised of a subset of species from more diverse forests, and the extent to which this pattern varied among taxa. At the landscape-scale the species-by-sites matrices were significantly nested for all nine taxonomic groups when both sites and species were sorted to maximally pack the species/occurrence matrix and, except for orchid bees when sorted by land-use intensity (primary forest to Eucalyptus plantation). Different patterns emerged when we conducted pairwise analyses of nestedness between the three forest types: (a) most of the taxonomic groups were nested in accordance with increased land-use intensity; (b) neither orchid bees nor leaf-litter amphibians from secondary forest made up a significant nested subset of primary forest species, although species found in Eucalyptus plantation sites were nested within secondary forest communities; and (c) lizards from Eucalyptus plantations were not a nested subset of either primary or secondary forest. Our findings emphasize the complex nature of patterns of species occupancy in tropical multiple-use forestry landscapes, and illustrate that there may be no easy solutions to questions regarding the conservation value of secondary and exotic plantation forests.     

The importance of traditional meadow management techniques for conservation of vascular plant species richness in Norway

Using information from a regional survey of vascular plants of 130 sites in western Norway, a selection of sites based on a heuristic iterative complementarity-based nature reserve selection procedure was performed. The results indicate that conservation of traditionally managed hay meadows is of major importance as they contributed 60.1% of all native species recorded; afforested grasslands (deciduous woodlands < 70 years old) contributed 26.8%, whereas artificially fertilized hay meadows and intensively cultivated grasslands taken together contributed 13.1% of the species. The species composition of the meadows was significantly nested. Thus, if you conserve the most species-rich meadows, you also conserve most of the species in the less species-rich meadows. Nestedness in meadows was significantly correlated with within-meadow habitat diversity and soil pH. The most species-rich meadows were traditional meadows, characterized by high habitat diversity and high soil pH. These meadows will support nearly all species including habitat specialists and regionally rare species, whilst artificially fertilized hay meadows only support the generalist subset, i.e. common species. Area was not significantly correlated with nestedness suggesting that it is more important to cover many habitats than to preserve large traditional meadows just because they are large.     

Nested plant and fungal communities; the importance of area and habitat quality in maximizing species capture in boreal old-growth forests

Knowledge of the distribution of rare species is crucial for species conservation in fragmented habitats. Species communities often exhibit nestedness, i.e. species in species-poor sites comprise a subset of richer ones. Thus, rare species are confined to species-rich sites. We evaluate whether plant and fungal communities in 46 old-growth spruce forest patches (0.17-12 ha) exhibit nestedness. The question whether a single large patch or several small patches capture most species (i.e. the SLOSS-issue) is evaluated in combination with species saturation analyses. All species groups exhibited significant nestedness. Area was generally related to nestedness, i.e. rare species were over-represented in the largest patches. Species saturation analysis indicated that large patches accumulated more Red-list species in patch interiors than small patches. Thus, rare and Red-list species were best captured in large patches. However, nestedness also emerged in equal sized sample plots, i.e. rare species were over-represented in high quality habitats. Thus, small habitats of high quality should not be neglected in a conservation perspective.     

Conservation in a city: Do the same principles apply to different taxa?

Factors shaping overall species richness and representation of endangered species of vascular flora and butterflies were determined in 48 nature reserves in Prague, Czech Republic. Total species richness of both groups, and the presence of endangered butterflies, reflect the present status of habitats, while that of endangered plants reflects habitat composition at the time of reserve establishment. Reserve area has a much stronger effect on the species richness of sessile plants than mobile butterflies which, especially endangered species, respond more positively to heterogeneity than to area. Both species richness and endangered species peak in reserves half covered with forest, likely because they harbor species of both woodland and non-woodland habitats, and edge specialists. Solely relying on area and disregarding habitat quality, or a failure to conserve small but high quality sites, may be counterproductive for conserving endangered plant and butterfly species. To conserve diversity of plants and butterflies current management practices, often aimed at maintaining large blocks of pre-selected plant communities, should change to include maintenance of fallows, edges and transient zones.     

The effect of the surrounding landscape matrix on mangrove bird community assembly in north Australia

Mangroves are highly threatened ecosystems yet their community ecology is poorly understood. We examined the ecological determinants of bird community assemblage in floristically depauperate mangroves. Birds were surveyed using line transect methods. Large mangrove patches supported fewer species than smaller patches. Patches did not comprise nested species subsets and the bird species richness of several small patches combined was greater than a single large area. The number of mangrove dependent species in a patch was area-dependent suggesting these species may be resource limited, although there was no species density compensation. There was a clear effect of the surrounding habitat, with matrix species accounting for ∼45% of bird species in a patch. Patches surrounded by tropical savanna were relatively species-poor, while regardless of size, patches including monsoon rainforest were relatively species rich. Null model analysis of non-random assemblage structure (nestedness and species co-occurrence) revealed no deterministic structure to the overall mangrove species assemblage. These analyses described a random pattern of bird distribution and with no evidence of density compensation this suggests that competition is a weak structuring force of mangrove bird assemblages. The lack of nestedness and the random co-occurrence of species are consistent with the matrix-dependence of bird community composition. Conservation plans should treat mangrove patches as part of a habitat mosaic and incorporate many smaller mangrove patches rather than just big ones. Consideration of the nature, extent and diversity of the surrounding matrices is vital in managing and conserving mangrove bird communities.     

Selecting terrestrial arthropods as indicators of small-scale disturbance: A first approach in the Brazilian Atlantic Forest

The growing pressure placed by human development on natural resources creates a need for quick and precise answers about the state of conservation of different areas. Thus, identifying and making use of ecological indicators becomes an essential task in the conservation of tropical systems. Here we assess the effects of small-scale disturbance on terrestrial arthropods and select groups that could be used as ecological indicators in the Brazilian Atlantic Forest. Arthropods were sampled within a continuous forest in the Serra do Mar State Park, southeastern Brazil, both in disturbed and undisturbed areas of the reserve. The abundance of exotic species was higher in the disturbed site, and this pattern seems to be an adequate indicator of anthropogenic disturbance. Species richness of Araneae, Carabidae, Scarabaeidae, Staphylinidae, and epigaeic Coleoptera (pooled) was higher in the undisturbed site, while that of fruit-feeding butterflies was higher in the disturbed site. Species richness was not significantly correlated between any pair of taxa. In contrast, species composition was significantly correlated among most groups, and clearly discriminates the disturbed from the undisturbed site. Moreover, fruit-feeding butterflies and epigaeic Coleoptera composition discriminated disturbed and undisturbed sites even when species were grouped into higher taxonomic levels, which may be a way of overcoming the difficulty of identifying arthropod species from poorly studied, species-rich ecosystems. Potential applications for these indicators include the choice and evaluation of sites for the establishment of natural reserves, elaboration of management plans, and the assessment of ecological impacts due to human activities, either for the purposes of licensing or legal compensation.     

Changes in nestedness in experimental communities of soil fauna undergoing extinction

Nestedness is the degree to which a set of communities represent different-sized subsets from the same ordered composition of species. Strong nestedness has been associated with communities presumably ordered by extinction – landbridge islands, habitat fragments – but development of nestedness in such systems due to extinction over time has rarely been followed. We examined the effects of local extinction on the nested structure of experimentally isolated nematode and microarthropod communities. Experiments were conducted in Georgia, USA, intact soil and litter microcosms, and Derbyshire, UK, in situ moss microecosystems. Nestedness increased initially, as predicted, but there was evidence of a decline in nestedness later in both experiments. Increasing nestedness was consistent with predictable losses of species, such as loss of less common species, predators, or species of large body size. We hypothesize that the later phase of declining nestedness was due to increasing disorder in species’ chance of extinction as the experiments progressed, with the resulting stochastic differentiation of communities reducing nestedness.     

Indicator species among resident forest birds - A cross-regional evaluation in northern Europe

In European forests, plants, fungi and invertebrates have been proposed as indicator species for assessing conservation value at the stand scale. To cover larger spatial scales, wide-ranging vertebrates could be added to that set of species. For resident forest birds, we (1) explored whether the occurrence of some species could be used to indicate high species richness and abundances, and (2) compared the results among four regions in the Baltic Sea drainage basin with a common species pool but different forest management intensities and varying proportions of deciduous and coniferous trees (south-central and southern Sweden, south-central Lithuania and northeastern Poland). Assemblages of deciduous forest birds in 100-ha landscape units were generally nested, suggesting that species richness within that group may be predicted based on the presence of a few species. Birds of coniferous forests, however, showed poorer conformity to nestedness in Sweden. Specialised species such as the middle spotted (Dendrocopos medius) and lesser spotted woodpeckers (D. minor) in deciduous forest and the three-toed woodpecker (Picoides tridactylus) in coniferous forest generally figured among the best indicators. In deciduous forest, there was high cross-regional consistency in the identity of the best indicators. Moreover, the sites where the best indicator was present also harboured higher relative abundances of most background species. For coniferous forest, however, such a relationship was not found. We conclude that an indicator species approach may be useful for resident birds of deciduous forests in hemiboreal Europe, emphasising that it should constitute one of many complementary tools for conservation management.     

Combined effects of habitat modification on trait composition and species nestedness in river invertebrates

Changes in catchment land-use and sedimentation have large ecological effects on rivers, but there is limited transferable understanding of the consequences for river conservation. In the Usk river system (Wales, UK), we assessed whether catchment-scale change in land-use and patch-scale sedimentation (i) affected organisms with specific life-history traits and (ii) resulted in nested assemblages with species-poor sites occupied mostly by sub-sets of organisms from richer sites.Reaches in catchments converted to agriculture had nested species assemblages characterised by greater representation of organisms with small body size, shorter life cycle and effective dispersal capacity. In contrast, richer sites in semi-natural catchments supported taxa with longer life cycles. Patch-scale sedimentation was also accompanied by nested patterns in which depauperate patches supported taxa mostly with shorter life cycles, small size and detrital feeding habits. Sediment-free patches were richer and characterised by larger taxa, poor dispersers and predators. Trait diversity was reduced by habitat modification at both scales.We conclude that habitat modification in this river catchment has led to the systematic drop-out at two different scales of specific groups of organisms with particular trait character. Large-scale agricultural intensification appears to have removed larger, longer-lived invertebrates that probably require stable conditions, and we advocate further studies to appraise whether such organisms are at risk more globally from land-use conversion. This river case study is one of the first to combine nestedness analysis with biological trait assessment and it might help in developing transferable methods to predict the conservation impacts of land-use change.     

Birds in Western Australian wheatbelt reserves—implications for conservation

Bird species richness in 22 reserves in the Western Australian wheatbelt was shown to be related not to isolation from adjacent uncleared land, either spatially or with time since clearing of land in their vicinity, but to area of reserve and certain reserve habitat variables. The nature of these relationships was examined with multiple regression analysis. Reserve area was the most important variable, except in some passerine groups, where numbers of plant species, vegetation associations, and plant life form and density classes in each vegetation stratum were, separately, more important than area. Eighty-two percent of the variation in the number of bird species was explained by area of reserve and number of plant species, indicating the importance of floristics to the total bird assemblage within reserves. The number of formations present (the broadest vegetation structural grouping used) did not explain any of the variation in species numbers in any of the bird groupings.There were more resident passerine species present in wheatbelt reserves than there were breeding passerine species on similar-sized southwestern Australian late-Pleistocene/Holocene islands, although the species versus area relationship of the resident habitat-specific passerines (P₅ group) was very similar to that of the island land-bird faunas. The P₅ species group contained many species which probably responded to wheatbelt reserves as islands; some of these species may fail to persist in the wheatbelt in the long term. Twenty-three species usually resident in reserves and 15 ‘non-residents’ were identified as being ‘vulnerable’ or of uncertain conservation status in the wheatbelt.Some vegetation formations within reserves were more important to birds than others; woodlands were most important both to resident and transient species. Most species do not appear to distinguish between shrublands and heaths as major habitats; Species richness versus formation area relationship suggest that insular patchiness for birds in the wheatbelt was manifest at the level of vegetation formations. Reserves as small as 80 ha were important sanctuaries for birds in the wheatbelt, although 1500 ha was considered a minimum area of reserve to conserve a local avifauna. Reserves of the order of 30,000–94,000 ha were required to contain most of the avifauna of the wheatbelt.     

The relationship between local extinctions of grassland butterflies and increased soil nitrogen levels

In contrast to many other western European countries, the knowledge about trends in the Swedish butterfly fauna is poor. We studied the effects of habitat and species characteristics on species turnover in 13 grassland sites in southern Sweden by comparing species richness and compositions at two separate occasions with an interval of 21 years. The mean number of species per site decreased from 30 to 24, with a large variation between sites. The number of extinctions was highest in sites where the proportion of trees and shrubs had increased most, but there was no detectable effect of area or of the composition of landscapes surrounding the sites. Areas protected as nature reserves had lost as many species as unprotected areas had, indicating both the importance of proper management of nature reserves and that nature reserves alone may not be enough to inhibit regional extinction of butterfly species. Species dependent on nutrient-poor conditions tended to decrease while species dependent on nutrient-rich conditions tended to increase, indicating a negative effect of increased soil nitrogen levels resulting from active fertilizing of pastures and/or atmospheric nitrogen deposition. A regular monitoring program could show whether our results are representative for Sweden or Northern Europe.     

Land snail distribution patterns within a site: The role of different calcium sources

The aims of this study were to analyse whether land snail assemblage patterns reflect the gradient of calcium content on a very small scale within a site. We chose two sites differing in their calcium richness and source of the calcium. The “Tufa site” had abundant tufa in the soil, while the “Boulder site” was on chemically inert chert bedrock where calcium originated from vegetation. On each site a set of 20 quadrats from which snails were extracted was laid down in a line from the calcium rich patch to the calcium poorer surround matrix. At the both sites, available calcium contents of topsoil decreased significantly with samples' position from the patch centre. For the Tufa site, calcium content was a strong controller not only of species composition but also species richness, total abundance, and abundances of almost all species. At the Boulder site only species composition was significantly driven by calcium. Species composition was highly nested along calcium gradient at the Tufa site contrary to the Boulder site where the species had an almost random distribution. We conclude that the best predictor of species composition was in both cases content of carbonate calcium in topsoil. Topsoil pH was positively correlated with calcium content only at the Tufa site.     

Effects of tropical forest fragmentation on aerial insectivorous bats in a land-bridge island system

Habitat fragmentation causes drastic changes in the biota and it is crucial to understand these modifications to mitigate its consequences. While studies on Neotropical bats have mainly targeted phyllostomid bats, impacts of fragmentation on the equally important aerial insectivores remain largely unexplored. We studied species richness, composition, count abundance and feeding activity of aerial insectivorous bats in a system of land-bridge islands in Panama with acoustic sampling. We predicted negative effects of fragmentation on forest species while bats foraging in open space should remain essentially unaffected. Rarefaction analyses indicated higher species richness for islands than mainland sites. For forest species, multivariate analyses suggested compositional differences between sites due to effects of isolation, area and vegetation structure. Contrary to our expectations, count abundance of forest species was similar across site categories. Feeding activity, however, was curtailed on far islands compared to near islands. As expected, bats hunting in open space did not reveal negative responses to fragmentation. Interestingly, they even displayed higher abundance counts on far and small islands. On the species level, two forest bats responded negatively to size reduction or site isolation, respectively, while a forest bat and a bat hunting in open space were more abundant on islands, irrespectively of island isolation or size. Our findings suggest that small forest remnants are of considerable conservation value as many aerial insectivores intensively use them. Hence high conservation priority should be given to retain or re-establish a high degree of forest integrity and low levels of isolation.     

Remnant grassland habitats as source communities for plant diversification in agricultural landscapes

Lately there has been a shift in Sweden from grazing species-rich semi-natural grasslands towards grazing ex-arable fields in the modern agricultural landscape. These fields normally contain a fraction of the plant species richness compared to semi-natural grasslands. However, small remnant habitats have been suggested as important for plant species diversity and conservation as they may function as refugia for grassland specialists in fragmented and highly modified agricultural landscapes. In this study, we examined whether plant communities on small remnant habitats, i.e. midfield islets, can function as sources for grassland species to disperse out into surrounding grazed ex-fields (former arable fields). We examined species richness and grassland specialists (species favoured by grazing) and their ability to colonize fields after 5 and 11 years of grazing. The fields that had been grazed for a shorter time were fairly species-poor with few grassland specialists. A longer period of grazing had a positive effect on total and small-scale species diversity in both islets and fields. Species composition became more similar with time, and the number of grassland specialists in both habitats increased. We found that grassland specialists dispersed step-wise into the fields, and the number of grassland specialists decreased with distance from the source. Our study suggests that remnant habitats, such as midfield islets, do function as a source community for grassland specialists and enhance diversification of grassland species when grazing is introduced. For long-term conservation of plant species, incorporating small refugia into larger grazing complexes may thus enhance species richness.     

The role of species—area relationships in reserve choice: A British example

The equilibrium theory of island biogeography (Mac Arthur & Wilson, 1967) presently dominates conservation studies. Reliance on the species—area relationship as a criterion for choosing reserves is critically examined using data for landbird species number on island reserves. It is suggested that taking several factors, rather than just area alone, is more meaningful when choosing between reserve sites. Data for islands or reserves can be interpreted without recourse to equilibrium theory; the case for its widespread acceptance is still unproven.     

The impact of marine reserves on nekton diversity and community composition in subtropical eastern Australia

The effectiveness of marine reserve protection on the biodiversity of aquatic assemblages (i.e. nekton) in subtropical eastern Australia was examined within two small (<6 km²) marine reserves and four non-reserve areas. The two marine reserves, and their corresponding non-reserves, were located in different geographical locations within Moreton Bay (north and south) and sites were surveyed with multiple hauls of a seine net. Species richness, evenness, density and mean size of the inshore communities were compared between the reserves and non-reserves. No statistical significant difference was detected in species richness between the areas however species evenness was significantly lower in the only non-reserve site impacted by commercial net fishing. Mean size of nekton was found to be significantly greater in the marine reserves compared to non-reserves but no statistical significant difference was found in the density of nekton between the study sites. Multivariate analysis revealed differences in community composition, particularly between the geographical locations where areas were impacted by different types of fishing pressure (recreational v commercial). These results highlight the impact commercial fishing can have on entire nekton assemblages, not just on targeted species. Our study demonstrates that the small marine reserves in Moreton Bay are protecting marine biodiversity and are thus at least partially achieving their management objective (to enhance the zone’s marine biodiversity).     

Understory plant species and functional diversity in the degraded wet tropical forests of Kolombangara Island,Solomon Islands

Anthropogenic activities have resulted in extensive deforestation and forest degradation on many tropical oceanic islands. For instance, some islands in the Solomon archipelago have as little as 10% of primary forests remaining with few of these remnants protected from future land use change. We examine the plant species and functional diversity (excluding adult canopy trees) of 48 sites from four forest land use types (two types of primary forest, secondary forest and abandoned tree plantations) and two common human-maintained land use types (coconut plantations and grazed pastures) across three elevation bands on Kolombangara Island, Solomon Islands. In total, we surveyed 384 species from 86 families of which only 6.5% were non-native. Species richness was lowest in coconut plantations and grazed pastures and declined with increasing elevation across all land use types. Functional diversity was similar between primary and secondary forest (high richness, high evenness and unaltered dispersion) and lowest in coconut plantations and grazed pastures. Our results suggest that species and functional richness have had divergent responses to land use change in forest land uses indicative of a loss of functional redundancy. Despite structural and compositional similarities among primary forests and degraded forest land uses, full recovery of secondary and commercial plantations has not been achieved. We suggest that conservation of Kolombangara’s forest understory flora will require reserves across the island’s elevation gradient and may require active restoration in the future, particularly if degrading activities continue at the current rate.     

Indicator species and the problem of spatial inconsistency in nestedness patterns

The potential as indicators of species richness were investigated for 178 species belonging to six ecologically defined species groups (epiphytic bryophytes on nutrient-rich bark, epiphytic macrolichens on nutrient rich bark, pendant lichens on conifer trees, bryophytes on siliceous rocks, bryophytes on dead conifer wood, and polypore fungi on dead conifer wood), using species data from 0.25 ha plots from three different coniferous forest areas (ca. 200 ha each). A species was defined as a potential indicator species for a species group within a study area if its distribution was statistically significantly nested within the species-plot matrix ranked according to species richness, and if the plot frequency of the species was less than 25%.Only two species were identified as potential indicators within all three areas and on average ≈80% of the potential indicator species were lost from one area to another. The results indicate that inconsistency between areas in the species’ frequency distributions and their position in nested hierarchies may strongly reduce the general predictive power of indicator species of species richness, even if significantly nested patterns are found at the community level. We suggest that indicators related to amount and quality of habitats may be an alternative to lists of indicator species of species richness.     

Plant species richness and composition in managed grasslands: The relative importance of field management and environmental factors

Decline of grassland diversity throughout Europe within the last decades is threatening biological diversity and is a major conservation problem. There is an urgent need to determine the underlying factors that control vascular plant species richness and composition in managed grasslands. In this study, 117 grasslands were sampled using standardised methods. Explanatory variables were recorded for each grassland site, reflecting the local field management, site-specific environmental conditions and large-scale spatial trends. Using variation partitioning methods, we determined the pure and shared effects of these three sets of explanatory variables on the plant species richness and composition in grasslands. Most of the explained variation in plant species richness was related to the joint effect of local field management and environmental variables. However, the applied variation partitioning approach revealed that the pure effect of spatial variables contributed relatively little to explaining variation in both the plant species richness and species composition. The largest fractions of explained variation in plant species composition were accounted for by the pure effects of environmental and local field management variables. Moreover, the results revealed that the main mechanisms by which these sets of explanatory variables affect plant species vary according to the type of management regime under study. From our findings we could conclude that particularly a reduction of nitrogen fertilisation on meadows and grazing at a low stocking rate on pastures can help to conserve biodiversity.