Latitudinal gradients of parasite species richness in primates

Infectious disease risk is thought to increase in the tropics, but little is known about latitudinal gradients of parasite diversity. We used a comparative data set encompassing 330 parasite species reported from 119 primate hosts to examine latitudinal gradients in the diversity of micro and macroparasites per primate host species. Analyses conducted with and without controlling for host phylogeny showed that parasite species richness increased closer to the equator for protozoan parasites, but not for viruses or helminths. Relative to other major parasite groups, protozoa reported from wild primates were transmitted disproportionately by arthropod vectors. Within the protozoa, our results revealed that vector‐borne parasites showed a highly significant latitudinal gradient in species richness. This higher diversity of vector‐borne protozoa near the tropics could be influenced by a greater abundance or diversity of biting arthropods in the tropics, or by climatic effects on vector behaviour and parasite development. Many vector‐borne diseases, such as leishmaniasis, trypanosomiasis, and malaria pose risks to both humans and wildlife, and nearly one‐third of the protozoan parasites from free‐living primates in our data set have been reported to infect humans. Because the geographical distribution and prevalence of many vector‐borne parasites are expected to increase because of global warming, these results are important for predicting future parasite‐mediated threats to biodiversity and human health.     

Shoot biomass and species richness in relation to some environmental factors in a coastal dune area in The Netherlands

Shoot biomass, species richness and selected environmental factors were studied at Meijendel, a coastal dune area in The Netherlands. The relationship between species richness and shoot biomass of the stand could be best described by a unimodal curve, with the peak at 300 g m^–2. Measures of species richness were positively correlated with soil water, nitrogen and phosphorus.Shoot biomass showed a positive correlation with soil water, nitrogen and humus at low levels of shoot biomass.Nomenclature of phanerogams and plant community types follows Heukels & van Ooststroom (1973), and Westhoff & den Held (1969) respectively.Publication of the Meijendel comité new series: 76.     

Macroecological patterns of spider species richness across Europe

We analysed the pattern of covariation of European spider species richness with various environmental variables at different scales. Four layers of perception ranging from single investigation sites to the whole European continent were selected. Species richness was determined using published data from all four scales. Correlation analyses and stepwise multiple linear regression were used to relate richness to topographic, climatic and biotic variables. Up to nine environmental variables were included in the analyses (area, latitude, elevation range, mean annual temperature, local variation in mean annual temperature, mean annual precipitation, mean July temperature, local variation in mean July temperature, plant species richness). At the local and at the continental scale, no significant correlations with surface area were found, whereas at the landscape and regional scale, surface area had a significant positive effect on species richness. Factors that were positively correlated with species richness at both broader scales were plant species richness, elevation range, and specific temperature variables (regional scale: local variation in mean annual, and mean July temperature; continental scale: mean July temperature). Latitude was significantly negatively correlated with the species richness at the continental scale. Multiple models for spider species richness data accounted for up to 77% of the total variance in spider species richness data. Furthermore, multiple models explained variation in plant species richness up to 79% through the variables mean July temperature and elevation range. We conclude that these first continental wide analyses grasp the overall pattern in spider species richness of Europe quite well, although some of the observed patterns are not directly causal. Climatic variables are expected to be among the most important direct factors, although other variables (e.g. elevation range, plant species richness) are important (surrogate) correlates of spider species richness.     

Density, body mass and parasite species richness of terrestrial mammals

We investigated the relationships between helminth species richness and body mass and density of terrestrial mammals. Cross-species analysis and the phylogenetically independent contrast method produced different results. A non-phylogenetic approach (cross-species comparisons) led to the conclusion that parasite richness is linked to host body size. However, an analysis using phylogenetically independent contrasts showed no relationship between host body size and parasite richness. Conversely, a non-phylogenetic approach generated a negative relationship between parasite richness and host density, whereas the independent contrast method showed the opposite trend – that is, parasite richness is positively correlated with host density. From an evolutionary perspective, our results suggest that opportunities for parasite colonization depend more closely on how many hosts are available in a given area than on how large the hosts are. From an epidemiological point of view, our results confirm theoretical models which assume that host density is linked to the opportunity of a parasite to invade a population of hosts. Our findings also suggest that parasitism may be a cost associated with host density. Finally, we provide some support for the non-linear allometry between density and mammal body mass (Silva and Downing, 1995), and explain why host density and host body mass do not relate equally to parasite species richness.     

Host ecology and life-history traits associated with blood parasite species richness in birds

Identifying host traits associated with the number of different parasite species or strains harboured by a particular host species can have important implications for understanding the impact of parasitism on hosts. We investigated associations between host ecology and life history, and parasite richness and prevalence of the four major avian blood parasite genera. We used an extensive data on blood parasite infections and host ecology in 263 bird species from the Western Palearctic, combining species-specific data with a comparative approach to control for similarity in phenotype among host species due to the effects of common phylogenetic descent. Adult survival rate negatively correlated with the number of parasite species infecting a host species when controlling for similarity due to common descent and body mass. In addition, the prevalence of Haemoproteus, Plasmodium and Leucocytozoon was higher in species harbouring a richer parasite assemblage. These results suggest that the impact on host fitness caused by avian haematozoa may be underestimated in natural populations if the exacerbated virulence associated with exposure to multiple parasites is not taken into account.     

Combining projected changes in species richness and composition reveals climate change impacts on coastal Mediterranean fish assemblages

Species Temporal Turnover (STT) is one of the most familiar metrics to assess changes in assemblage composition as a consequence of climate change. However, STT mixes two components in one metric, changes in assemblage composition caused by a process of species loss or gain (i.e. the nestedness component) and changes in assemblage composition caused by a process of species replacement (i.e. the species replacement component). Drawing on previous studies investigating spatial patterns of beta diversity, we propose measures of STT that allow analysing each component (species replacement vs. nestedness), separately. We also present a mapping strategy to simultaneously visualize changes in species richness and assemblage composition. To illustrate our approach, we used the Mediterranean coastal fish fauna as a case study. Using Bioclimatic Envelope Models (BEMs) we first projected the potential future climatic niches of 288 coastal Mediterranean fish species based on a global warming scenario. We then aggregated geographically the species‐level projections to analyse the projected changes in species richness and composition. Our results show that projected changes in assemblage composition are caused by different processes (species replacement vs. nestedness) in several areas of the Mediterranean Sea. In addition, our mapping strategy highlights that the coastal fish fauna in several regions of the Mediterranean Sea could experience a ‘cul‐de‐sac’ effect if exposed to climate warming. Overall, the joint exploration of changes in species richness and composition coupled with the distinction between species replacement and nestedness bears important information for understanding the nature of climate change impacts on biodiversity. These methodological advances should help decision‐makers in prioritizing action in the areas facing the greatest vulnerability to climate.     

Species richness of Protozoa in Japanese lakes

The protozoan fauna and species richness in the pelagic zone of 15 Japanese lakes were investigated in 1996 using polyurethane foam (PF) substrates. The most common species were flagellates, such as Cryptomonas erosa, Oikomonas termo, and Pleuromonas jaculans. Cinetochilum margaritaceum and Actinophrys sol were the most common species of the Ciliata and Sarcodina, respectively. The similarity of species occurrence was calculated from presence/absence data, but this revealed no clear trend with respect to the influence of lake properties such as trophic state, surface area, or mean depth. The occurrence pattern of Protozoa was most similar in L. Chuzenji and L. Biwa (north basin), two oligomesotrophic natural lakes. Log species richness was positively correlated with log total phosphorus (r = 0.54, P < 0.05) and negatively with log mean depth (r = −0.58, P < 0.05). The diversity index (Margalef's formula), highly correlated with the total species number (r = 0.85, P < 0.01), was negatively correlated with log lake area (r = −0.71, P < 0.01). The logarithm of Phytomastigophora number was positively correlated with log total nitrogen (r = 0.53, P < 0.05), and the logarithm of Ciliata number was negatively correlated with log lake area (r = −0.55, P < 0.05). The species richness of Protozoa on PF substrates was determined by both the nutrient status of the lake and the distance from the location of the suspended PF substrate to the lake bottom or shore. Received: September 25, 1999 / Accepted: January 6, 2000     

Propagule pressure and native species richness effects drive invasibility in tropical dry forest seedling layers

Understanding the factors that encourage or inhibit plant invasions is vital to focusing limited invasive control efforts within areas where they are most practical and cost-effective. To extend the range of contexts in which invasibility is studied and aid the development of practical strategies to limit damaging plant invasions, we set out to test the relative importance of native species richness, native seedling density, and invasive propagule pressure, on the invasibility of artificial assemblages of naturally occurring tropical woody seedling communities. Our greenhouse mesocosms included a species pool of twelve trees and woody shrubs native to South Florida's tropical hardwood hammocks, and an increasingly prevalent noxious woody invader of this system, Ardisia elliptica. We found that invader propagule pressure was the single most important factor determining community invasibility. We also revealed a positive relationship between invasibility and native species richness in our polyculture mesocosms. Because A. elliptica biomass production significantly differed among different native monocultures and was not related to overyielding in native polycultures, we suggest that the effect of species richness on invasibility in this experiment was the result of sampling effects rather than a true effect of diversity.Three broad findings hold potential for application in preventing and controlling plant invasions, especially in the seedling layers of tropical dry forests: (1) effective invasive control efforts will likely benefit from measures to minimize propagule pressure; (2) managers might do well to prioritize invasive monitoring and removal efforts on the most diverse habitats within a management region; and (3) while more data are necessary to further understand our finding of a lack of association between productivity and invasibility, management regimes aimed at maximizing primary productivity might not increase invasibility, and in fact, strategies for controlling invasive plants via the management of ecosystem productivity may be ineffective.     

Effects of river level fluctuation on plant species richness, diversity, and distribution in a floodplain forest in Central Amazonia

River levels in Central Amazonia fluctuate up to 14 m annually, with the flooding period ranging from 50 to 270 days between the rising and falling phases. Vast areas of forest along the rivers contain plant species that are well adapted to annual flooding. We studied the effect of flooding level on tree species richness, diversity, density, and composition in lake, river, and stream habitats in Jaú National Park, Brazil. 3051 trees >10 cm diameter (at 1.3 m diameter at breast height, dbh) were measured and identified in 25 10 m × 40 m randomly selected plots in each habitat. Ordination methods and analysis of variance results showed that forested areas near lakes had significantly lower species richness of trees than riverine and streamside habitats. Plot species richness and diversity were strongly negatively correlated with the water level and duration of flooding. The drier (stream) habitat had more total species (54 species of trees) and more unique species of trees (6 tree species) than the riverine (52 tree species; 3 unique species) and lake (33 tree species; 3 unique species) habitats. Species composition overlap among habitats was surprisingly high (42.6–60.6% overlap), almost one-third of the species were found in all three habitat types, and few species were unique to each habitat. We conclude that: (1) duration of flooding has a strong impact on species richness, diversity and plant distribution patterns; (2) most species are adapted to a wide range of habitats and flood durations; and (3) while flood duration may decrease local diversity, it also creates and maintains high landscape-scale diversity by increasing landscape heterogeneity. Received: 20 April 1997 / Accepted: 14 January 1999     

Determining the relative roles of species replacement and species richness differences in generating beta‐diversity patterns

Aim To determine the relative contribution of species replacement and species richness differences to the emergence of beta‐diversity patterns. Innovation A novel method that disentangles all compositional differences (β_cc, overall beta diversity) in its two components, species replacement (β_‐3) and species richness differences (β_rich) is proposed. The performance of the method was studied with ternary plots, which allow visualization of the influence of the relative proportions of shared and unique species of two sites over each metric. The method was also tested in different hypothetical gradients and with real datasets. The novel method was compared with a previous proposal based on the partitioning of overall compositional differences (β_sor) in replacement (β_sim) and nestedness (β_nes). The linear response of β_cc contrasts with the curvilinear response of β_sor to linear gradients of dissimilarity. When two sites did not share any species, β_sim was always 1 and β_‐3 only reached 1 when the number of exclusive species of both sites was equal. β_‐3 remained constant along gradients of richness differences with constant replacement, while β_sim decreased. β_rich had a linear response to a linear gradient of richness differences with constant species replacement, whereas β_nes exhibited a hump‐shaped response. Moreover, β_sim > β_nes when clearly almost all species of one site were lost, whereas β_‐3 < β_rich in the same circumstances. Main conclusions The behaviour of the partition of β_cc into β_‐3 and β_rich is consistent with the variation of replacement and richness differences. The partitioning of β_sor into β_sim and β_nes overestimates the replacement component and underestimates richness differences. The novel methodology allows the discrimination of different causes of beta‐diversity patterns along latitudinal, biogeographic or ecological gradients, by estimating correctly the relative contributions of replacement and richness differences.     

Factors associated with plant species richness in a coastal tall‐grass prairie

Abstract. In this study we examine the factors associated with variations in species richness within a remnant tall‐grass prairie in order to gain insight into the relative importance of controlling variables. The study area was a small, isolated prairie surrounded by wetlands and located within the coastal prairie region, which occurs along the northwestern Gulf of Mexico coastal plain. Samples were taken along three transects that spanned the prairie. Parameters measured included micro‐elevation, soil characteristics, indications of recent disturbance, above‐ground biomass (including litter), light penetration through the plant canopy, and species richness. Species richness was found to correlate with micro‐elevation, certain soil parameters, and light penetration through the canopy, but not with above‐ground biomass. Structural equation analysis was used to assess the direct and indirect effects of micro‐elevation, soil properties, disturbance, and indicators of plant abundance on species richness. The results of this analysis showed that observed variations in species richness were primarily associated with variations in environmental effects (from soil and microtopography) and were largely unrelated to variations in measures of plant abundance (biomass and light penetration). These findings suggest that observed variations in species richness in this system primarily resulted from environmental effects on the species pool. These results fit with a growing body of information that suggests that environmental effects on species richness are of widespread importance.     

West African rivers as biogeographic islands: species richness of fish communities

Summary Some factors influencing the species richness of West African fish communities were studied in a sample of 26 rivers using four habitat and hydrologic variables. Analysis of a larger sample of 39 rivers showed that species richness was positively related to area. A power function with an exponent of 0.32 gave the best fit. As the surface area used was that of the catchment area and not that (unknown) of the river, the biological significance of this relationship and the possibilities of comparison were limited. Ridge regression analysis and forward stepwise selection indicated that a model that explained ln(species richness) as a function of ln(mean annual discharge) and ln-(catchment surface area) was best, accounting for 90% of the variance of the dependent variable. The combination of surface area and discharge was presumed to act through the volume of water available for the fishes and habitat productivity. Habitat diversity, measured by the diversity of the terrestrial vegetation covering the catchment area, had no significant positive effect when surface area was used in the regression. Rivers (islands) should have fewer species than tributaries of similar size since, for fishes within a river system (continent), there is free circulation between all its branches. The model derived from the river data underestimated the species richness of a sample of 11 tributaries. This was compatible with the hypothesis of higher population extinction rates in insular biotopes. The residuals of the linear model did not show random geographical distribution; the rivers in some areas had more species than expected. The possibility that historical factors, especially Quaternary climatic variations, might cause this distribution is discussed.     

Invasion rates increase with species richness in a marine epibenthic community by two mechanisms

It is widely believed that, when extrinsic conditions are similar, the likelihood of species invading established assemblages decreases with increasing species richness of the recipient community. Here we show that, for a sessile marine invertebrate community, invasion of patches increases with richness of the patch. We show that invasions can increase with local species richness by two distinct mechanisms. In the first, opportunistic colonisers with traits typical of invasive species colonise species-rich patches at higher rates because speciose patches are dominated by small colonies and mortality rates of small colonies are greater than that of large ones. Thus, mortality provides bare space for opportunists to colonise more frequently in species-rich patches. In the second, some species avoid colonising open areas of free space but preferentially associate with established colonies of particular other species, and a given preferred associate is more likely to occur in species-rich than in species-poor patches. These patterns are the result of particular properties of individual species and local species dynamics, and show that reduced risk of invasion is not necessarily an intrinsic property of species-rich communities. We conclude that resistance to invasion will be determined by the properties of the particular component species and emergent dynamics of the recipient community, and not by an aggregate community property such as richness.     

The relationship between productivity and multiple aspects of biodiversity in six grassland communities

Biodiversity is a multifaceted concept but most studies examining the association between the biodiversity of a community and its productivity focus only on species richness. Consequently, studies are needed to examine how other facets of biodiversity vary with productivity if we want to have a better understanding of the distribution of biodiversity across our planet. We evaluated how a number of biodiversity measures (species richness, evenness, dominance, rarity, Simpson’s diversity, and Shannon–Weiner diversity) varied across natural productivity gradients at 6 grassland sites in the continental US. Variation in productivity did not account for a substantial amount of variation in any measure of biodiversity at small spatial scales (≈1 m²) at most sites. When productivity accounted for substantial variation in biodiversity, different measures of biodiversity responded to productivity in different ways. For example, dominance changed in a U-shaped fashion along a productivity gradient whereas richness increased in an asymptotic fashion. Consequently, diversity indices, which account for both species richness and evenness, varied in a hump-shaped fashion along the productivity gradient. Our results highlight that an exclusive focus on the association between species richness and productivity provides an incomplete picture of how a community’s biodiversity is related to its functioning.     

Multi-annual changes in the parasite communities of rabbitfish Siganus rivulatus (Siganidae) in the Gulf of Aqaba, Red Sea

The parasite communities of the rabbitfish, Siganus rivulatus, were used to track multi-annual changes in the northern Gulf of Aqaba, Red Sea, in an environment subjected to ongoing anthropogenic impact. Parasitological data from these fish were collected from 1998 to 2000, with spring and fall samplings at three locations: at a coral reef (OBS), at a sandy beach area (NB) and at a mariculture cage farm (FF). These data were compared with data from 1995–1997 as well as data collected during 1981–1985 at the coral reef sampling site. The data analyses indicate that the ratio between heteroxenous and monoxenous parasite species declined significantly at all sites between 1995–1997 and 1998–2000. During the same period, the species richness of monoxenous parasites increased significantly at all sites. The species richness of heteroxenous parasites decreased significantly at the coral reef site, but remained steady at the other two sites. This coincided with a significant increase in the prevalence of monogeneans at the OBS and FF sites and a significant decrease in the prevalence of digeneans at the FF and NB sites. The decline in the abundance of the latter, specifically of Opisthogonoporoides sp. and Gyliauchen sp., was even more significant when compared with the 1981–1985 data. The prevalence of other gut helminths, namely the digenean Hexangium sigani and the nematodes Cucullanus sigani and Procamallanus elatensis, however, showed a significant increase over the same period. Analysis of the species richness and diversity indices of the parasite communities did not reveal conspicuous differences. These, however, did become apparent when heteroxenous and monoxenous members of particular taxa were analyzed separately. Therefore, when using parasite assemblages to detect ecological changes, it is essential to analyze not only at the community level, but also to consider separate components of particular parasitic groups. Communicated by H. von Westernhagen, A. Diamant     

Fine-scale spatial variation in plant species richness and its relationship to environmental conditions in coastal marshlands

Previous studies have shown that variations in environmental conditions play a major role in explaining variations in plant species richness at community and landscape scales. In this study, we considered the degree to which fine-scale spatial variations in richness could be related to fine-scale variations in abiotic and biotic factors. To examine spatial variation in richness, grids of 1 m² plots were laid out at five sites within a coastal riverine wetland landscape. At each site, a 5 × 7 array of plots was established adjacent to the river’s edge with plots one meter apart. In addition to the estimation of species richness, environmental measurements included sediment salinity, plot microelevation, percent of plot recently disturbed, and estimated community biomass. Our analysis strategy was to combine the use of structural equation modeling (path modeling) with an assessment of spatial association. Mantel’s tests revealed significant spatial autocorrelation in species richness at four of the five sites sampled, indicating that richness in a plot correlated with the richness of nearby plots. We subsequently considered the degree to which spatial autocorrelations in richness could be explained by spatial autocorrelations in environmental conditions. Once data were corrected for environmental correlations, spatial autocorrelation in residual species richness could not be detected at any site. Based on these results, we conclude that in this coastal wetland, there appears to be a fine-scale mapping of diversity to microgradients in environmental conditions.     

Patterns of composition and species richness of crustaceans and aquatic insects along environmental gradients in Mediterranean water bodies

Differences in the dynamics of ecological processes between Mediterranean and colder temperate aquatic systems could imply different patterns in faunal communities in terms of composition and biodiversity (i.e. species richness and rarity). In order to identify some of these patterns the crustacean and aquatic insect composition and biodiversity of four water body types, classified according to their salinity and water permanence, were compared. Moreover, the relationships between species richness and water, pond and landscape variables were analysed. A total number of 91 water bodies located throughout Catalunya (NE Iberian Peninsula) were sampled. Three species assemblages were observed: one for permanent freshwaters, another for temporary freshwaters, and a third one for saline waters (SW), since permanent and temporary saline water bodies had similar composition. Differences in salinity were associated with proportion of crustaceans versus insects and with singularity. Thus, saline ponds had a higher proportion of crustaceans, and lower values of singularity. Conductivity was significantly related to total (crustaceans plus insects) richness, and also related to insect richness. The main difference between the models obtained for crustacean species richness and insect species richness is the significance of landscape variables in the latter, and this fact could be related to the different dispersion types of these two faunal groups: active for insects versus passive for crustaceans. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Guest editors: R. Céréghino, J. Biggs, B. Oertli & S. Declerck The ecology of European ponds: defining the characteristics of a neglected freshwater habitat