Significant Species-area Relationship Research Articles

Landscape, Human Disturbance, and Climate Factors Drive the Species Richness of Alien Invasive Plants on Subtropical Islands.

Invasive alien plants (IAPs) pose a significant threat to island biodiversity and severely impact ecosystems. Understanding the species-area relationship and environmental determinants of growth forms for IAP species on subtropical islands is crucial for establishing an IAP's early warning mechanism, enhancing island ecological management, and protecting the ecosystems of Fujian and other subtropical islands. The study identified significant species-area relationships for IAPs and different life-form plants (trees, shrubs, and herbs), with slopes of 0.27, 0.16, 0.15, and 0.24, respectively. The small island effect does not apply to all species. Isolation has little effect on species richness, and the IAPs on Fujian islands do not conform to the isolation effect in island biogeography. Landscape factors are the main determinants of IAPs and different life-form species richness, with area, shape index, and perimeter-area ratio being the three primary landscape factors. These environmental factors are closely related to habitat heterogeneity. Besides landscape factors, different life forms respond differently to environmental factors. Climate drives the species richness distribution of shrubs and herbs, while trees are mainly influenced by human activities. Overall, landscape, human disturbance, and climate jointly drive the distribution of IAPs, with landscape factors being the most significant.

The use of fynbos fragments by birds: Stepping-stone habitats and resource refugia

Fynbos habitats are threatened by fragmentation through land use and anthropogenic changes in fire regimes, leading to a loss of suitable habitat for birds. We investigated the response of fynbos-typical avifauna to fragmentation and postfire vegetation age in order to better understand the consequences of these processes for bird communities. Vegetation composition and bird inventory data were collected along wandering transects in three South Outeniqua Sandstone Fynbos habitat configurations: fragmented patches (associated with anthropogenically driven habitat loss < 150 years ago), naturally isolated fynbos islands (formed through climate-driven forest expansion in the Holocene) and extensive areas of relatively pristine habitat known as ‘mainland’. The latter configurations served as references against which to investigate bird and vegetation responses to more recent habitat fragmentation. Linear regressions were used to compare the relationships of a number of bird and plant species to areas between each habitat configuration. Bird attribute frequency data were compared between habitat configurations using chi-square tests. Birds and plants showed significant species–area relationships in natural island and mainland sites, but no such relationship occurred in artificial fragments for birds, where the surrounding anthropogenic land uses are likely to have contributed generalist or colonist species. Avifaunal migratory groups were not affected by isolation distances of > 10 km in this study and their frequencies were the same across the three habitat configurations. Certain feeding guilds did, however, respond to postfire vegetation age, with nectarivore species twice as likely to occur in oldgrowth mainland fynbos. Fragmentation can alter fire disturbance regimes, which in turn alter the availability of resources in a habitat, so the impacts of fragmentation on birds are probably indirect through changes in the vegetation component.Conservation implications: Fragments of South Outeniqua Sandstone Fynbos have value as resource refugia and ‘stepping-stone’ reserves for avifauna. Fragments should be managed for vegetation age to ensure that at least some patches sustain high levels of nectarproducing plant species. Fire management should, however, factor in both plant and bird requirements.Keywords: Avifauna; Agricultural Mosaic; Cape Floristic Region; Conservation; Habitat Fragmentation; Species-Area Relationships

Nested patterns in urban butterfly species assemblages: respective roles of plot management, park layout and landscape features

Increasing numbers of cities are currently developing sustainable policies aimed at promoting urban biodiversity and ecological dynamics through the planning of green networks and the implementation of more sustainable management practices. These human activities can strongly influence environmental factors on which the organization of ecological communities at different scales depends. Thus, it is of fundamental importance to understand the relative impact of local management, green space design and landscape features on the distribution and the abundance of species in urban areas. On the basis of 2 years of butterfly surveys in urban public parks within an extensive Mediterranean metropolitan area, Marseille (South-East France), the aim of this paper is to provide a better understanding of the effect of these three environmental scales (plot, park, landscape) on the composition and organization of species assemblages. Using variation partitioning and nestedness analysis on ecological data aggregated at plot-level and park-level respectively, we demonstrate the preponderant effect of landscape scale features on urban butterfly assemblages. Our results also highlight an important co-variation of plot management, park layout and urban landscape features, in their interaction with the community structure of urban butterflies. Although there is no significant species-area relationship, significantly nested patterns arise in species composition. Selective colonization appears as a driving force constraining the constitution of species assemblages within the city. However, a prospective study on adjacent more natural areas suggests that biotic limitations, interspecific competition and habitat filtering may play an important role if a larger portion of the urbanization gradient is explored, which remains to be investigated.

Theory of island biogeography on a microscopic scale: organic aggregates as islands for aquatic pathogens

Four predictions of the MacArthur-Wilson theory of island biogeography were evaluated to assess the degree to which detrital-based organic aggregates (e.g. marine snow, organic detritus, and bioflocs) may provide a favorable microhabitat (i.e. an 'island') for bacteria in general, and specifically aquatic pathogens. We demonstrate the theory's relevance for microbial communities in aquatic environments by describing the community metabolic response and functional diversity of individual organic aggregates while documenting the persistence of potential pathogens and fecal indica- tor bacteria. Our results support the 4 predictions, including a significant species-area relationship, con- sistency of species richness at equilibrium, non-zero level of species turnover at equilibrium, and variance to mean ratios of less than 0.5 at equilibrium. The aggre- gate-associated microbial communities demonstrated significantly higher rates of metabolic response and functional diversity, and contained higher concentra- tions of culturable vibrios and fecal indicator bacteria compared to aggregate-free water, supporting the idea that organic aggregates are sites of favorable habitat surrounded by a less favorable matrix. These results substantiate that organic aggregates may be repre- sented as microscopic islands. Using island biogeogra- phy theory to understand the microbial ecology of aquatic pathogens associated with organic aggregates is important with respect to environmental sampling of recreational waters and mathematical modeling of the transmission of waterborne diseases from aquatic reservoirs to humans.

Biogeographical patterns of blood parasite lineage diversity in avian hosts from southern Melanesian islands

AbstractAim (1) To describe the species–area relationships among communities of Plasmodium and Haemoproteus parasites in different island populations of the same host genus (Aves: Zosterops). (2) To compare distance–decay relationships (turnover) between parasite communities and those with potential avian and dipteran hosts, which differ with respect to their movement and potential to disperse parasite species over large distances.Location Two archipelagos in the south‐west Pacific, Vanuatu and New Caledonia (c. 250 km west of Vanuatu) and its Loyalty Islands, with samples collected from a total of 16 islands of varying sizes (328–16,648 km2).Methods We characterized parasite diversity and distribution via polymerase chain reaction (PCR) from avian (Zosterops) blood samples. Bayesian methods were used to reconstruct the parasite phylogeny. In accordance with recent molecular evidence, we treat distinct mitochondrial DNA lineages as equivalent to species in this study. Path analysis and parasite lineage accumulation curves were used to assess the confounding effect of inadequate sampling on the estimation of parasite richness. Species–area and species–distance relationships were assessed using linear regression: distance–decay relationships were assessed using Mantel tests.Results Birds and mosquito species and Plasmodium lineages exhibited significant species–area relationships. However, Plasmodium lineages showed the weakest ‘species–area’ relationship; no relationship was found for Haemoproteus lineages. Avian species richness influenced parasite lineage richness more than mosquito species richness did. Within individual avian host species, the species–area relationship of parasites showed differing patterns. Path analysis indicated that sampling effort was unlikely to have a confounding effect on parasite richness. Distance from mainland (isolation effect) showed no effect on parasite richness. Community similarity decayed significantly with distance for avifauna, mosquito fauna and Plasmodium lineages but not for Haemoproteus lineages.Main conclusions Plasmodium lineages and mosquito species fit the power‐law model with steeper slopes than found for the avian hosts. The lack of species–distance relationship in parasites suggests that other factors, such as the competence of specific vectors and habitat features, may be more important than distance. The decay in similarity with distance suggests that the sampled Plasmodium lineages and their potential hosts were not randomly distributed, but rather exhibited spatially predictable patterns. We discuss these results in the context of the effects that parasite generality may have on distribution patterns.

Plant diversity in sacred forest fragments of Western Ghats: a comparative study of four life forms

The effect of fragmentation on different life forms within tropical forest plant communities is poorly understood. We studied the effect of degree of fragmentation and surrounding matrix on trees, lianas, shrubs and epiphytes in tropical forest fragments of Kodagu, Western Ghats, India. These fragments exist as sacred groves amidst a highly modified agricultural landscape, and have been preserved by the religious sentiments of local communities. Plants were sampled at two sites in continuous forests and 11 forest fragments. A total of 122 species of trees, 29 species of lianas, 60 species of shrubs and 66 species of epiphytes were recorded. Trees exhibited a significant species–area relationship (R2 = 0.74). Richness estimates after controlling for stem density (rarefaction) revealed that observed species–area relationship was not an artefact of passive sampling. Variation in species richness of the other three groups was explained by stem density and structural diversity. Linear distance from the reserve forest did not explain any variation in species richness. All life forms exhibited significant nested pattern. Trees were nested along the area gradient while nestedness in the other three groups showed evidence in support of habitat nestedness. The four life forms thus responded variably to degree of fragmentation. Our study revealed that 74% of the regional diversity for trees was contributed by diversity among plots, highlighting the importance of inter-patch habitat diversity in maintaining the total regional species pool. We conclude that trees alone cannot serve as good indicator for taking appropriate conservation measures to mitigate species loss resulting from habitat fragmentation.

Latitudinal variation of diversity in European freshwater animals is not concordant across habitat types

ABSTRACTAim We analysed the variation of species richness in the European freshwater fauna across latitude. In particular, we compared latitudinal patterns in species richness and β‐diversity among species adapted to different habitat types.Location Europe.Methods We compiled data on occurrence for 14,020 animal species across 25 pre‐defined biogeographical regions of European freshwaters from the Limnofauna Europaea. Furthermore, we extracted information on the habitat preferences of species. We assigned species to three habitat types: species adapted to groundwater, lotic (running water) and lentic (standing water) habitats. We analysed latitudinal patterns of species richness, the proportion of lentic species and β‐diversity.Results Only lentic species showed a significant species–area relationship. We found a monotonic decline of species richness with latitude for groundwater and lotic habitats, but a hump‐shaped relationship for lentic habitats. The proportion of lentic species increased from southern to northern latitudes. β‐Diversity declined from groundwater to lentic habitats and from southern to northern latitudes.Main conclusions The differences in the latitudinal variation of species richness among species adapted to different habitat types are in part due to differences in the propensity for dispersal. Since lentic habitats are less persistent than lotic or groundwater habitats, lentic species evolved more efficient strategies for dispersal. The dispersal propensity of lentic species facilitated the recolonization of central Europe after the last glaciation. Overall, we stress the importance of considering the history of regions and lineages as well as the ecological traits of species for understanding patterns of biodiversity.

Testing species–stone area and species–bryophyte cover relationships in riverine macroinvertebrates at small scales

Summary1. The species–area relationship is considered amongst the few genuine laws in ecology. Although positive species richness–stone area relationships have been found previously in stream systems, very few studies have simultaneously examined species–individuals, individuals–area, species–bryophyte biomass and individuals–bryophyte biomass relationships. We examined these relationships based on temporally replicated assessments of macroinvertebrates on stones at two river sites.2. We found only one significant species–area relationship out of six relationship tested, and two significant individuals–area relationships. Even these significant relationships were weak, however. By contrast, we detected significant and rather strong relationships between species richness and the number of individuals at both river sites on all three sampling dates. We also found significant relationships of both species richness and the number of individuals with bryophyte biomass at both river sites on all sampling occasions. One of the river sites was disturbed by a bulldozer, and the species–bryophyte biomass relationships were somewhat stronger after the disturbance event.3. Our findings are quite surprising, given that there were very weak species–area relationships on stream stones. By contrast, our results suggest a pivotal role for bryophyte biomass in determining the species richness and the number of individuals of stream macroinvertebrates at this small scale. The most probably origin of these relationships begins with bryophyte cover, which determines the number of individuals, and subsequently passively affects species richness. Thus, there is not necessarily a direct mechanism that determines the variability of species richness on stream stones.4. Experimental studies are needed to disentangle the various mechanisms (e.g. passive sampling, provision of more food, more niche space, flood disturbance refugia) by which bryophyte biomass affects stream macroinvertebrates.

Orchids of the West Indies: predictability of diversity and endemism

AbstractAim We examined phytogeographical patterns of West Indian orchids, and related island area and maximum elevation with orchid species richness and endemism. We expected strong species–area relationships, but that these would differ between low and montane island groups. In so far as maximum island elevation is a surrogate for habitat diversity, we anticipated a strong relationship with maximum elevation and both species richness and endemism for montane islands.Location The West Indies.Methods Our data included 49 islands and 728 species. Islands were classified as either montane (≥ 300 m elevation) or low (< 300 m). Linear and multivariate regression analyses were run to detect relationships between either area or maximum island elevation and species richness or the number of island endemic species.Results For all 49 islands, the species–area relationship was strong, producing a z‐value of 0.47 (slope of the regression line) and explaining 46% of the variation. For 18 relatively homogeneous, low islands we found a non‐significant slope of z = −0.01 that explained only 0.1% of the variation. The 31 montane islands had a highly significant species–area relationship, with z = 0.49 and accounting for 65% of the variation. Species numbers were also strongly related to maximum island elevation. For all islands < 750 km2, we found a small‐island effect, which reduced the species–area relationship to a non‐significant z = 0.16, with only 5% of the variation explained by the model. Species–area relationships for montane islands of at least 750 km2 were strong and significant, but maximum elevation was the best predictor of species richness and accounted for 79% of the variation. The frequency of single‐island endemics was high (42%) but nearly all occurred on just nine montane islands (300 species). The taxonomic distribution of endemics was also skewed, suggesting that seed dispersability, while remarkable in some taxa, is very limited in others. Montane island endemics showed strong species–area and species–elevation relationships.Main conclusions Area and elevation are good predictors of orchid species diversity and endemism in the West Indies, but these associations are driven by the extraordinarily strong relationships of large, montane islands. The species richness of low islands showed no significant relationship with either variable. A small‐island effect exists, but the montane islands had a significant relationship between species diversity and maximum elevation. Thus, patterns of Caribbean orchid diversity are dependent on an interplay between area and topographic diversity.

Nestedness of bird assemblages in fragmented Afromontane forest: the effect of plantation forestry in the matrix

Bird species composition (61 species) of Afromontane forest fragments ( n = 19) embedded in a natural grassland matrix or a plantation forestry matrix were compared. Forest bird assemblages in a natural grassland matrix displayed a nested non-random species distribution. Species loss was significantly area-dependent and predictable. Assemblages in the plantation-dominated matrix were also nested but were neither area- nor isolation-dependent and these potential processes had equal influence over bird species composition. Forests patches <50 ha in plantation were more species rich than those in a grassland matrix and visa versa for patches >50 ha. The effect of the matrix is revealed here with arboreal plantation cover promoting dispersal across the landscape, favouring abundant generalist bird species in smaller patches than expected in the plantation matrix, and the loss of some specialists and species living at low densities from large (>50 ha) patches. Because of a significant species–area relationship and possible area-dependent extinction, the largest forest patch in the nested series in a grassland matrix protects most bird species (89%). However, in a plantation matrix the absence of a species–area relationship requires the combination of many larger forest patches to protect most bird species. Plantation forests in the matrix significantly alter forest bird assemblage structure and composition. To avoid the effects of insularisation and to maintain the viability of bird communities in Afromontane forests requires conservation of the larger forests in a natural matrix. However, for forests in a plantation matrix, the management of dispersal processes by manipulation of the matrix may be as important to conserving species and communities as is minimising extinctions. Avoiding placing plantations near large forests, increasing the size of small patches, and where afforestation is unavoidable, placing plantations in the vicinity of small rather than large forest patches, are preferable management practices.

Species diversity and endemism of five major Malesian islands: diversity–area relationships

AbstractAim A comparison of biodiversity patterns within Malesia in relation to surface area.Location Analysis of the patterns in species richness and endemism of vascular plants in the five major Malesian islands, i.e. Java, Sulawesi, Sumatra, Borneo and New Guinea.Methods Available data on species richness and species ranges in correlation with the surface area of the respective islands were examined in this work. Estimations of total species numbers for these islands are presented based on extrapolation of all available published Flora Malesiana information and recent checklists, all in all comprising 12,000 different species. The regression analysis of overall species richness and endemism were studied for all species together as well as for different plant families to compare the fit with the Arrhenius species–area model.Results The five islands form a series of independent areas of increasing size suited for an analysis of the species–area relationships at the regional scale. All species taken together and those of families with even distribution throughout Malesia show significant species–area relationships. Non‐significant relationships were detected in families with western or eastern‐centred Malesian distribution patterns. Relationships between number of endemic species and surface area are significant for all species and for the majority of the families with significant species–area relationships.Main conclusions Species–area relationships of families appear to be dependent on species number. Families with high numbers of species usually have a significant species–area relationship whereas small families have not. For the families that display an eastern or western Malesian centred pattern, a historical biogeographical explanation should be invoked. Island surface area appears to be a predictor for island percent endemism in Malesian vascular plants. None of the islands appears to be a hotspot of endemism nor of species diversity, as no significant departure from the Arrhenius model was noted for any of them.

Biodiversity on urban roundabouts—Hemiptera, management and the species–area relationship

Summary The biodiversity of insects within urban areas has been relatively little studied. Given the large and ever increasing extent of urban areas, and that the insect species richness there can be high, it is important to know the factors determining that aspect of biodiversity. In this study two of these factors, namely habitat management and area, were considered. Arboreal and grassland Hemiptera, and grassland plants, were sampled on 18 roundabouts and other road enclosed sites in the town of Bracknell. Hemiptera were sampled using suction sampling and tree beating. A significant species–area relationship was found for arboreal Hemiptera, which was strongly related to habitat diversity. For both grassland plants and Hemiptera, grassland management, by mowing, had a significant effect on species richness. Despite the management grassland plants showed a significant species–area relationship. However the effect of management on Hemiptera was great enough to outweigh any area effect. As the size of open spaces is often constrained in urban areas, altering habitat management has a greater potential for enhancing biodiversity. For arboreal Hemiptera choice of trees for planting is of particular importance, while for grassland Hemiptera diversity would be increased with a reduction in the intensity of management, such a reduction in the frequency of mowing.

Forest Fragments in East-central Illinois: Islands or Habitat Patches for Mammals?

We surveyed the nonvolant mammals in 10 forest fragments embedded in a matrix of row crop agriculture in east-central Illinois to assess the impact of forest fragmentation on mammalian diversity and distributions. A total of 19 species were recorded during our study, including 16 native species that occur naturally in forest habitat. We found a significant species-area relationship and a significantly nested subset structure. In particular, gray squirrels, chipmunks and flying squirrels were only encountered in the larger, more continuous sites suggesting a negative effect of habitat fragmentation. Seven species were ubiquitous and we believe that several others occur periodically at all study sites, indicating that most mammalian species currently present have not had their distributions altered by changes in the intervening habitat. Though an analogy to oceanic islands may apply for some species, we believe that most mammals treat forest remnants as habitat patches rather than islands, and that mechanisms such as habitat selection, constraints due to home range size and differential dispersal ability best explain the observed distributions of mammals.

Feeding Specialisation and Host Distribution of British and Finnish Prunus Feeding Macrolepidoptera

Of 81 macrolepidopteran species found in both Britain and Finland, 46 feed on Prunus species in both countries, 19 feed on Prunus species in Britain but not in Finland and 18 feed on Prunus species in Finland but not in Britain. In Finland all the Prunus feeding species feed on Prunus padus which is the most abundant Prunus species. In Britain 80% of the Prunus feeding species feed on P. spinosa which is the most abundant Prunus species. In both Britain and Finland P. domestica is the second most important host, 34% of the British and 22% of the Finnish species being found on it. Significant species-area relationships exist for both Finnish and British Prunus species. In general the shared species of macrolepidoptera show the same feeding specialisation, i.e. generalists are generalists in both Finland and Britain, nevertheless certain host specific species in Finland are generalists in Britain and vice versa. Insect taxonomy, familial characteristics and geographical limits of host plants and insect species all contribute to the changes seen in feeding specialisation from country to country

Habitat islands and the equilibrium theory of island biogeography: testing some predictions.

Species-area data from a study of marsh birds are used to test five predictions generated by the equilibrium theory of island biogeography. Three predictions are supported: we found a significant species-area relationship, a non-zero level of turnover, and a variance-mean ratio of 0.5. One prediction is rejected: the extinction rates were not greater on small islands. The results of one test are equivocal: the number of species on each island was not always the same. As Gilbert (1980) suggests, a strong species-area relationship alone does not validate the theory. The avian communities we studied were on habitat islands, not true islands, and underwent complete extinction annually. Thus caution must be used before applying the theory to these and other habitat islands.

The Biogeography of the Lizards of the Seychelles Islands

The distributions of the eighteen species of lizards found in the Seychelles are given so far as they are known. The indigenous lizards of the granitic islands are endemic, at least at the specific level, and generally exhibit racial differentiation between island populations. The species-area relationship for the granitic islands is shallow, and there is little evidence for species turnover as predicted by the equilibrium theory of island biogeography. Low immigration rates arising from the isolation of the granitic Seychelles, together with low extinction rates due to climatic stability and high population densities may be responsible for this. The saurian faunas of the coralline islands are impoverished, with species not distinct from Madagascan and pantropical species. It is suggested that this has resulted from a recent sea-level stand higher than the present, which submerged the very low lying islands. Low rates of species immigration have not allowed the islands to attain a species equilibrium. This is supported by the presence of unfilled niches and the absence of a significant species-area relationship. The equilibrium model of island biogeography is of little relevance to the distribution of the Seychelles lizard fauna.

Insect herbivore guilds and species—area relationships: leafminers on British trees

Abstract. 1. 239 species of leafmining insects have been recorded from thirty‐seven species of trees and large shrubs in Britain.2. A significant species—area relationship was obtained for these insects, but it explained only 19% of the variation about the regression he. A further 23% of the variation may be accounted for by taxonomic relationship of host plants.3. A significant correlation was established between the number of species of leafminers and those of mesophyll‐feeding leafhoppers for twentyeight host tree species. Both guilds are dominated by host specific feeders.4. It is suggested that species—area effects are important in determining species richness of phytophagous insects mainly when groups of closely related host plants are considered. With more diverse arrays of hosts, taxonomic influences, which are probably mainly chemical, may outweigh such area related effects.