Habitat diversity, ecological requirements of species and the Small Island Effect

Aim  To explore the causal factors leading to a significant Small Island Effect (SIE), that is, the absence of the commonly found species–area relationships below an island size, on the terrestrial isopod communities from a large number of islands.
Location  Ninety islands of the Aegean Sea (Greece).
Methods  The detection of a significant SIE is assessed through the application of all three methods available in the literature. Species are divided into generalists and specialists. We tested if the minimum area and the area range of each species' occurrences differ between generalists and specialists. Next, we searched for differences in the ratios of specialists to generalists above and below the SIE threshold, and tested their cumulative ratios when islands are arranged according to increasing area, altitude or habitat diversity in order to identify the threshold where they become statistically indistinguishable from the ratio of the total set of islands.
Results  Our results indicate a strong effect of habitat availability on the SIE. Communities of islands within the SIE range, host a higher percentage of generalists. An analysis of the specific habitat requirements shows that, for isopods, the crucial factor is the lack of habitats related to inland waters from small islands.
Main conclusions  The distribution of habitats on islands of different size is of major importance for the occurrence of a SIE. The relative representation of specialist and generalist species on islands of different size plays an important role in shaping SIE-related patterns. Conservation efforts should pay special attention on freshwater habitats, especially on small Aegean islands. Identifying the causal factors of SIE, combined with a thorough knowledge of the ecological requirements of species can offer insights into identifying habitat types and groups of species that are more vulnerable to alterations of the environment.     

Distribution and Diversity of Primates in Guyana: Species-Area Relationships and Riverine Barriers

Species-area relationships predict that there is a positive relationship between the number of species and the size of an area. It has been suggested that species richness will covary with area because larger areas have a greater diversity of habitats. Moreover, habitat diversity may operate in conjunction with riverine barriers to influence primate biogeography. Few studies have determined if and how these hypotheses relate to primate diversity in Guyana. To test these biogeographic hypotheses, I used data from 1,725 km of primate surveys I conducted in Guyana. I estimated geographic ranges for each of the 8 primate species via a GIS system. Geographic range size is a major determinant of the number of sightings of the 8 primate species. Primate species diversity is strongly negatively correlated with the number of rivers crossed moving in a clockwise pattern from eastern to NW Guyana. Interfluvial and habitat areas influence primate species diversity in Guyana. However, my data on primate biogeography in Guyana do not support the hypothesis that habitat diversity within the interfluvial areas effects primate diversity. Although the species-area relationship is considered the closest thing to a rule in ecology, researchers should be wary of too readily applying and accepting the model at all scales in biogeographic studies.     

Phytogeography of the Kaieteur Falls, Potaro Plateau, Guyana: floral distributions and affinities

Aim The plant diversity of one location on the Guiana Shield, Kaieteur National Park in Guyana, is used to examine the various hypothesized origins of the flora and to evaluate which may best explain the current plant distributions. Location Kaieteur National Park is located on eastern edge of the Potaro Plateau in central Guyana, South America. The species examined have distributions that vary from local to global. Methods The distribution patterns of the families, genera and species known from Kaieteur are examined using generalized distribution patterns. Results Data on distribution patterns, elevation and habitat were gathered from 131 flowering plant families, 517 genera and 1227 species. These plants represent all taxa that are currently known to occur in the area of the original Kaieteur National Park. Families tend to have cosmopolitan or pantropical distribution, genera are mostly neotropical and at the species level, most species are restricted to the Guiana Shield (c. 40%), northern South America (69%) or neotropical (96%) in distribution, each level inclusive of the previous. Conclusions The flora at the study site in Kaieteur National Park has its strongest affinity with the Guiana Shield; 42.1% of the species have a distribution that corresponds with the Shield or is more restricted within the Shield. There is a distinct flora on the Guiana Shield and its affinities lie with the flora of northern South American and beyond that, the neotropics. The flora is not closely affiliated with the floras of the Brazilian Shield, the Amazon, the Andes, the eastern coastal forests of Brazil, southern South America, or Africa as has been previous suggested.     

Niche analysis of orchids of serpentine and non-serpentine areas: Implications for conservation

Orchids are known for their species richness, intriguing ecology, rarity and the fact that they grow in almost all terrestrial ecosystems. Although numerous studies about their ecology have been carried out concerning calcareous areas, little is known about orchids that occur in serpentine habitats. The aim of this study was to investigate the ecological preferences of orchids in serpentine and non-serpentine areas on the model of the Valjevo Mountain Range (W Serbia). Niche analysis of orchids was performed using outlying mean index analysis. Data concerning geographical coordinates, altitude, habitat type, inclination, bedrock type, light regime, soil moisture, acidity, nitrogen and temperature were used as explanatory variables. Data of 33 orchid taxa from 407 localities were analysed. The most important gradients that govern orchid distribution were geological bedrock, light regime and temperature. The results have shown that only Anacamptis morio and Gymnadenia conopsea have statistically significantly larger populations on serpentine compared with non-serpentine bedrocks. This study highlights the importance of serpentine habitats as orchid habitats, bearing in mind the occurrence of rare species and species which were found exclusively in serpentine habitats.     

Interactive effects of warming,eutrophication and size structure: impacts on biodiversity and food‐web structure

Warming and eutrophication are two of the most important global change stressors for natural ecosystems, but their interaction is poorly understood. We used a dynamic model of complex, size‐structured food webs to assess interactive effects on diversity and network structure. We found antagonistic impacts: Warming increases diversity in eutrophic systems and decreases it in oligotrophic systems. These effects interact with the community size structure: Communities of similarly sized species such as parasitoid–host systems are stabilized by warming and destabilized by eutrophication, whereas the diversity of size‐structured predator–prey networks decreases strongly with warming, but decreases only weakly with eutrophication. Nonrandom extinction risks for generalists and specialists lead to higher connectance in networks without size structure and lower connectance in size‐structured communities. Overall, our results unravel interactive impacts of warming and eutrophication and suggest that size structure may serve as an important proxy for predicting the community sensitivity to these global change stressors.     

High proportion of smaller ranged hummingbird species coincides with ecological specialization across the Americas

Ecological communities that experience stable climate conditions have been speculated to preserve more specialized interspecific associations and have higher proportions of smaller ranged species (SRS). Thus, areas with disproportionally large numbers of SRS are expected to coincide geographically with a high degree of community-level ecological specialization, but this suggestion remains poorly supported with empirical evidence. Here, we analysed data for hummingbird resource specialization, range size, contemporary climate, and Late Quaternary climate stability for 46 hummingbird–plant mutualistic networks distributed across the Americas, representing 130 hummingbird species (ca 40% of all hummingbird species). We demonstrate a positive relationship between the proportion of SRS of hummingbirds and community-level specialization, i.e. the division of the floral niche among coexisting hummingbird species. This relationship remained strong even when accounting for climate, furthermore, the effect of SRS on specialization was far stronger than the effect of specialization on SRS, suggesting that climate largely influences specialization through species'' range-size dynamics. Irrespective of the exact mechanism involved, our results indicate that communities consisting of higher proportions of SRS may be vulnerable to disturbance not only because of their small geographical ranges, but also because of their high degree of specialization.     

Geographical range size and host specificity in ectoparasites: a case study with Amphipsylla fleas and rodent hosts

Aim  To identify the factors that determine the geographical range sizes of ectoparasites with different degrees of host specificity.
Location  The study used data on the distributions of fleas of the genus Amphipsylla and their rodent hosts across the Holarctic.
Methods  All known points of occurrence of 32 flea species and 51 species of their rodent hosts were mapped. The shape and size of the geographical range of each species were estimated using a combination of the minimal convex polygon technique and modelling with the garp algorithm. Factors determining the geographical range sizes of the fleas were identified using stepwise multiple regression analysis.
Results  The geographical range size of fleas that are strongly host-specific across their entire ranges correlated positively with the geographical range size of the fleas' principal hosts, and negatively with the geographical range size of the fleas' potential competitors. The geographical range sizes of both (1) fleas that are locally host-specific but that shift their host preferences geographically, and (2) host-opportunistic fleas were positively correlated only with the area of the geographical ranges of their principal hosts. Strongly host-specific fleas occupied 0.2–80.0% of the geographical range of their principal hosts, whereas this figure was 0.9–83.7% in locally host-specific fleas and 16.6–63.7% in host-opportunistic fleas.
Main conclusions  The main determinant of the geographical range size of a flea species is the size of the geographical range of its hosts. The role of potential competitors in determining the geographical range size is stronger in host-specific than in host-opportunistic fleas. Cases in which the geographical range of a parasite is smaller than the geographical range(s) of its host(s) owing to narrower parasite environmental tolerances are much more frequent in host-opportunistic than in host-specific fleas.     

The distribution–abundance (density) relationship: its form and causes in a tropical mammal order, Primates

Aim Across a wide variety of organisms, taxa with high local densities (abundance) have large geographical ranges (distributions). We use primatology's detailed knowledge of its taxon to investigate the form and causes of the relationship in, unusually for macroecological analysis, a tropical taxon. Location Africa, Central and South America, Asia, Madagascar. Methods To investigate the form of the density–range relationship, we regressed local density on geographical range size, and also on female body mass, because in the Primates, density correlates strongly with mass. To investigate the biological causes of the relationship, we related (1) abundance (density × range size) and (2) residuals from the density–range regression lines to various measures of (i) resource use, (ii) reproductive rate and (iii) potential specialization. All data are from the literature. Analyses were done at the level of species (n = 140), genera (n = 60) and families/subfamilies (n = 17). We present various levels of results, including for all data, after omission of outlier data, after correction for phylogenetic dependence, and after Bonferroni correction of probabilities for multiple comparisons. Results Regarding the form of the relationship, Madagascar primates are clear outliers (high densities in small ranges). Among the remaining three realms, the relation of density to range is weak or non‐existent at the level of species and genera. However, it is strong, tight and linear at the level of families/subfamilies (r² = 0.6, F_1,10 = 19, P < 0.01). Although among primates, density is very significantly related to mass, at no taxonomic level is range size related to body mass. Consequently, removing the effects of mass makes little to no difference to density–range results. Regarding the biology of the relationship, only traits indicative of specialization are associated with abundance (meaning numbers): rare taxa are more specialized than are abundant taxa. The association is largely via range size, not density. Across families, no traits correlate significantly with the density–range relationship, nor with deviations from it, despite the strength of the relationship at this taxonomic level. Main conclusions We suggest that in macroecology, analysis at taxonomic levels deeper than that of the relatively ephemeral species can be appropriate. We argue that the several purely methodological explanations for the positive density–range size relationship in primates can be rejected. Of the various biological hypotheses, those having to do with specialization–generalization seem the only applicable ones. The fact that the relationship is entirely via range size, not via density, means that while we might have a biology of range size, we do not yet have one of the density–geographical range relationship. It is probably time to search for multivariate explanations, rather than univariate ones. However, we can for the first time, for at least primates, suggest that any association of abundance or range size with specialization is via the number of different subtaxa, not the average degree of specialization of each subtaxon. The implication for conservation is obvious.     

Diversity of Rock-Inhabiting Cyanobacterial Lichens: Studies on Granite Inselbergs along the Orinoco and in Guyana

Abstract: A survey was undertaken of specialized saxicolous cyanobacterial lichens growing on exposed granitic rock surfaces of inselbergs in Venezuela and additionally in Guyana and French Guyana. The study focused on taxonomy and species composition. Twenty-three cyanobacterial lichens were found, four of which are new to science: Peltula auriculata, Phylliscum vermiformis, Psorotichia polyspora and Pterygiopsis guyanensis. Besides the new species, almost all taxa are absent from the available lists of lichen-forming fungi from the Guyana region. Although free-living cyanobacteria are the dominant group in biological crusts covering the inselbergs, the number of cyanobacterial lichens is relatively high and their distribution is homogenous over long distances and macro-climatic gradients. As inselberg rock faces undergo relatively fast weathering under moist tropical climates, numerous micro-habitats are formed. Among these, xeric micro-habitats are favourable for colonization by cyanobacterial lichens, mainly of the Lichinaceae and Peltulaceae. It is concluded that granite inselbergs in the savannas of the Orinoco lowland and the Guyana region are local centres of diversity for saxicolous cyanobacterial lichens.     

Modelled spatial distribution of marine fish and projected modifications in the North Atlantic Ocean

The objectives of this work were to examine the past, current and potential influence of global climate change on the spatial distribution of some commercially exploited fish and to evaluate a recently proposed new ecological niche model (ENM) called nonparametric probabilistic ecological niche model (NPPEN). This new technique is based on a modified version of the test called Multiple Response Permutation Procedure (MRPP) using the generalized Mahalanobis distance. The technique was applied in the extratropical regions of the North Atlantic Ocean on eight commercially exploited fish species using three environmental parameters (sea surface temperature, bathymetry and sea surface salinity). The numerical procedure and the model allowed a better characterization of the niche (sensu Hutchinson) and an improved modelling of the spatial distribution of the species. Furthermore, the technique appeared to be robust to incomplete or bimodal training sets. Despite some potential limitations related to the choice of the climatic scenarios (A2 and B2), the type of physical model (ECHAM 4) and the absence of consideration of biotic interactions, modelled changes in species distribution explained some current observed shifts in dominance that occurred in the North Atlantic sector, and particularly in the North Sea. Although projected changes suggest a poleward movement of species, our results indicate that some species may not be able to track their climatic envelope and that climate change may have a prominent influence on fish distribution during this century. The phenomenon is likely to trigger locally major changes in the dominance of species with likely implications for socio‐economical systems. In this way, ENMs might provide a new management tool against which changes in the resource might be better anticipated.     

Geographic variation in body form of prehistoric Jomon males in the Japanese archipelago: Its ecogeographic implications

Diversity of human body size and shape is often biogeographically interpreted in association with climatic conditions. According to Bergmann's and Allen's rules, populations in regions with a cold climate are expected to display an overall larger body and smaller/shorter extremities than those in warm/hot environments. In the present study, the skeletal limb size and proportions of prehistoric Jomon hunter‐gatherers, who extensively inhabited subarctic to subtropical areas in the ancient Japanese archipelago, were examined to evaluate whether or not the inter‐regional differences follow such ecogeographic patterns. Results showed that the Jomon intralimb proportions including relative distal limb lengths did not differ significantly among five regions from northern Hokkaido to the southern Okinawa Islands. This suggests a limited co‐variability of the intralimb proportions with climate, particularly within genealogically close populations. In contrast, femoral head breadth (associated with body mass) and skeletal limb lengths were found to be significantly and positively correlated with latitude, suggesting a north‐south geographical cline in the body size. This gradient therefore comprehensively conforms to Bergmann's rule, and may stem from multiple potential factors such as phylogenetic constraints, microevolutionary adaptation to climatic/geographic conditions during the Jomon period, and nutritional and physiological response during ontogeny. Specifically, the remarkably small‐bodied Jomon in the Okinawa Islands can also be explained as an adjustment to subtropical and insular environments. Thus, the findings obtained in this study indicate that Jomon people, while maintaining fundamental intralimb proportions, displayed body size variation in concert with ambient surroundings. Am J Phys Anthropol, 2012. © 2012 Wiley Periodicals, Inc.     

Biogeography of the Amazon molly: ecological niche and range limits of an asexual hybrid species

Aim To understand the relative contributions of environmental factors, dispersal limitations and the presence of sperm donors in determining the distribution of the Amazon molly (Poecilia formosa), a sperm‐dependent unisexual fish species of hybrid origin. To explore niche similarities and/or differences between the hybrid and parental species. To evaluate whether large‐scale abiotic factors can explain a successful introduction of both P. formosa and Poecilia latipinna. Location South‐east United States, Mexico and Central America. Methods We used abiotic variables in ecological niche modelling (ENM) to identify regions with suitable conditions for the presence of the Amazon molly and its two parental species (P. latipinna and Poecilia mexicana). We also used a recently developed metric to calculate the degree of niche overlap between the hybrid and its parental species. Results ENM produced highly significant models [all area under the curve (AUC) > 0.99 for the three species]. Annual mean temperature and minimum temperature of the coldest month were the variables that best explained the distribution of the Amazon molly. With the exception of south Florida, few areas beyond the known distribution of the species were predicted to have suitable environmental conditions. The hybrid species niche overlaps partially with the parental species. However, given the available data, it is neither more similar nor more different than expected by chance. Main conclusions Two different processes are acting to limit the distribution of P. formosa. At the northern limit, although a sperm donor species is present further north, suitable environmental conditions are absent from nearby locations. At the southern limit, a sperm donor species is present and areas with good environmental conditions are present at nearby locations, suggesting that dispersal ability is the limiting factor. We found that the hybrid species overlaps in a similar way with both parental species while still having its own niche identity. This result may be explained by the fact that hybrid species inherit characteristics of two ecologically divergent species, which can result in intermediate or even transgressive phenotypes. These results support recent work on the role of hybridization in diversification.     

Biogeography and the structure of coral reef fish communities on isolated islands

Aim To determine the applicability of biogeographical and ecological theory to marine species at two remote island locations. This study examines how biogeography, isolation and species geographic range size influence patterns of species richness, endemism, species composition and the abundance of coral reef fishes. Location Christmas Island and the Cocos (Keeling) Islands in the tropical eastern Indian Ocean. Methods Published species lists and underwater visual surveys were used to determine species richness, endemism, species composition and abundance of reef fishes at the islands. These data were statistically compared with patterns of species composition and abundance from the neighbouring ‘mainland’ Indonesian region. Results The two isolated reef fish communities were species‐poor and contained a distinct taxonomic composition with an overrepresentation of species with high dispersal potential. Despite low species richness, we found no evidence of density compensation, with population densities on the islands similar to those of species‐rich mainland assemblages. The mix of Indian and Pacific Ocean species and the proportional representations of the various regional faunas in the assemblages were not influenced by the relative proximity of the islands to different biogeographical provinces. Moreover, species at the edge of their range did not have a lower abundance than species at the centre of their range, and endemic species had substantially higher abundances than widespread species. At both locations, endemism was low (less than 1.2% of the community); this may be because the locations are not sufficiently isolated or old enough to promote the evolution of endemic species. Main conclusions The patterns observed generally conform to terrestrial biogeographical theory, suggesting that similar processes may be influencing species richness and community composition in reef fish communities at these remote islands. However, species abundances differed from typical terrestrial patterns, and this may be because of the life history of reef fishes and the processes maintaining isolated populations.     

Distribution range and ecological niche of Primula marginata Curtis (Primulaceae)

The distribution range of Primula marginata Curtis (Primulaceae) has never been fully characterized. In the present study, authors did a revision of the distribution range using herbaria material, database records and in situ populations' check-up. P. marginata was confirmed extending from Cottian to Maritime and Ligurian Alps, with few outlier occurrences in the northern Apennines. The localities previously reported from northern Piedmont (Val d'Ossola) were not confirmed. Maximum entropy model (Maxent) was used to simulate the potential distribution of P. marginata under current climate conditions. According to the distribution modelling performed, the species prefers rocky calcareous habitats mainly at high elevations, with abundant precipitation, but low moisture retention at soil level and marked temperature range between winter and summer seasons. The potential distribution area drawn by Maxent seemed to describe P. marginata at its maximum extension, and any future climate changes might cause limitations for the survival of the species.     

Niche breadth,environmental landscape,and physical barriers: their importance as determinants of species distributions

Species distributions and their patterns in geographical space have been studied for several decades and explained by theories such as Janzen's, with respect to the nature of dispersal barriers in the Tropics, and Rapoport's, with respect to range size. However, the roles of specific environmental and geographical factors (e.g. ecological niche breadth, geographical barriers, etc.) in shaping species ranges and distributional patterns remain largely unexplored. The present study analyzed predictions from these two theories via analysis of virtual species with respect to biogeographical patterns: virtual species were created across South America, covering all major environments on the continent, and were used to compare effects of niche breadth, environmental availability, connectivity, seasonality, and the presence of known biogeographical barriers (rivers) in shaping species distributions and biodiversity patterns. Geographical ranges varied from narrow to broad, depending on the location of the seed point when comparing species produced with the same niche breadth. Analysis without consideration of seasonality and barriers produced species with broader distributions in the Tropics and narrower distributions in montane and temperate regions of the continent. When seasonality was included, however, broader ranges were concentrated in temperate regions, thus supporting Janzen's idea. Rapoport's rule of broader geographical ranges at higher latitudes was supported only when seasonality and physical barriers were included but not in species with very narrow or very broad niches, suggesting that this ‘rule’ results from interactions among niche breadth, dispersal capabilities, and dispersal barriers. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 108 , 241–250.