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Local Richness (local + richness)

Distribution by Scientific Domains

Life Sciences	69%

Selected Abstracts

The evolutionary species pool hypothesis and patterns of freshwater diatom diversity along a pH gradient

JOURNAL OF BIOGEOGRAPHY, Issue 3 2005
Jason Pither
Abstract Aim, To interpret the unimodal relationship between diatom species richness and lake pH within the context of the evolutionary species pool hypothesis (SPH). We test the following primary prediction arising from the SPH: the size of the potential species pool (PSP) will increase along a gradient representing the historical commonness of different pH environments (pH commonness). To do this we assume that the present-day spatial dominance of near-neutral pH conditions compared with acidic and alkaline conditions reliably mimics the relative spatial availabilities of historical pH conditions among freshwater lakes. We also determine whether local richness represents a constant proportion of PSP size along the pH commonness gradient. Location, Two hundred and thirty-four lakes distributed over a 405,000 km2 region of the north-eastern United States of America. Methods, Sediment diatom morphospecies lists and pH data were acquired from the US Environmental Protection Agency's Environmental Monitoring and Assessment Program (EMAP) website. Using 248 morphospecies that occurred in at least 10 of the 234 lakes, four different measures of PSPs were calculated along the pH gradient. Local species richness was equated with the number of species occurring within the lake. Alpha diversity was equated with the average species richness of lakes with similar pH values. A combination of statistical methods were employed, including correlations, quadratic regression and piecewise regression. Results, PSP size increased significantly with pH commonness for all four measures of PSP size, thus supporting the primary prediction of the evolutionary SPH. Local richness comprised a larger proportion of the PSP within acidic lakes than within circumneutral lakes. Alpha diversity and lake species richness both increased significantly with pH commonness, but the former did so in a two-step fashion. We test and reject several alternative contemporary time-scale explanations for our findings. Main Conclusions, Our findings are consistent with the hypothesis that diatom taxonomic richness is presently lower within acidic and highly alkaline lakes than in circumneutral lakes owing to the limited opportunity in space and/or time for the evolution of suitably adapted species. Whereas ecological processes can explain why certain species are excluded from particular habitats, e.g. acidic lakes, they cannot account for why so few species are adapted to those habitats in the first place. [source]

Are local patterns of anthropoid primate diversity related to patterns of diversity at a larger scale?

JOURNAL OF BIOGEOGRAPHY, Issue 6 2000
M. J. Lawes
Abstract Aims, (1) To determine the relationship between local and regional anthropoid primate species richness. (2) To establish the spatial and temporal scale at which the ultimate processes influencing patterns of primate species coexistence operate. Location Continental landmasses of Africa, South America and Asia (India to China, and all islands as far south as New Guinea). Methods, The local,regional species richness relationship for anthropoid primates is estimated by regressing local richness against regional richness (independent variable). Local richness is estimated in small, replicate local assemblages sampled in regions that vary in total species richness. A strong linear relationship is taken as evidence that local assemblages are unsaturated and local richness results from proportional sampling of the regional pool. An asymptotic curvilinear relationship is interpreted to reflect saturated communities, where strong biotic interactions limit local richness and local processes structure the species assemblage. As a further test of the assumption of local assemblage saturation, we looked for density compensation in high-density local primate assemblages. Results, The local,regional species richness relationship was linear for Africa and South America, and the slope of the relationship did not differ between the two continents. For Asia, curvilinearity best described the relationship between local and regional richness. Asian primate assemblages appear to be saturated and this is confirmed by density compensation among Asian primates. However, density compensation was also observed among African primates. The apparent assemblage saturation in Asia is not a species,area phenomenon related to the small size of the isolated islands and their forest blocks, since similar low local species richness occurs in large forests on mainland and/or peninsular Asia. Main conclusions In Africa and South America local primate assemblage composition appears to reflect the influence of biogeographic processes operating on regional spatial scales and historical time scales. In Asia the composition of primate assemblages are by-and-large subject to ecological constraint operating over a relatively small spatial and temporal scale. The possible local influence of the El Niño Southern Oscillations on the evolution and selection of life-history characteristics among Asian primates, and in determining local patterns of primate species coexistence, warrants closer inspection. [source]

Local richness and distribution of the lizard fauna in natural habitat mosaics of the Brazilian Cerrado

AUSTRAL ECOLOGY, Issue 1 2009
CRISTIANO NOGUEIRA
Abstract We investigate local lizard richness and distribution in central Brazilian Cerrado, harbouring one of the least studied herpetofaunas in the Neotropical region. Our results are based on standardized samplings at 10 localities, involving 2917 captures of 57 lizard species in 10 families. Local richness values exceeded most presented in earlier studies and varied from 13 to 28 species, with modal values between 19 and 28 species. Most of the Cerrado lizard fauna is composed of habitat-specialists with patchy distributions in the mosaic of grasslands, savannas and forests, resulting in habitat-structured lizard assemblages. Faunal overlap between open and forested habitats is limited, and forested and open areas may act as mutual barriers to lizard distribution. Habitat use is influenced by niche conservatism in deep lineages, with iguanians and gekkotans showing higher use of forested habitats, whereas autarchoglossans are richer and more abundant in open habitats. Contrary to trends observed in Cerrado birds and large mammals, lizard richness is significantly higher in open, interfluvial habitats that dominate the Cerrado landscape. Between-localities variation in lizard richness seems tied to geographical distance, landscape history and phylogenetic constraints, factors operating in other well-studied lizard faunas in open environments. Higher richness in dominant, open interfluvial habitats may be recurrent in Squamata and other small-bodied vertebrates, posing a threat to conservation as these habitats are most vulnerable to the fast, widespread and ongoing process of habitat destruction in central Brazil. [source]

Plant species richness and environmental heterogeneity in a mountain landscape: effects of variability and spatial configuration

ECOGRAPHY, Issue 4 2006
Alexia Dufour
The loss of biodiversity has become a matter of urgent concern and a better understanding of local drivers is crucial for conservation. Although environmental heterogeneity is recognized as an important determinant of biodiversity, this has rarely been tested using field data at management scale. We propose and provide evidence for the simple hypothesis that local species diversity is related to spatial environmental heterogeneity. Species partition the environment into habitats. Biodiversity is therefore expected to be influenced by two aspects of spatial heterogeneity: 1) the variability of environmental conditions, which will affect the number of types of habitat, and 2) the spatial configuration of habitats, which will affect the rates of ecological processes, such as dispersal or competition. Earlier, simulation experiments predicted that both aspects of heterogeneity will influence plant species richness at a particular site. For the first time, these predictions were tested for plant communities using field data, which we collected in a wooded pasture in the Swiss Jura mountains using a four-level hierarchical sampling design. Richness generally increased with increasing environmental variability and "roughness" (i.e. decreasing spatial aggregation). Effects occurred at all scales, but the nature of the effect changed with scale, suggesting a change in the underlying mechanisms, which will need to be taken into account if scaling up to larger landscapes. Although we found significant effects of environmental heterogeneity, other factors such as history could also be important determinants. If a relationship between environmental heterogeneity and species richness can be shown to be general, recently available high-resolution environmental data can be used to complement the assessment of patterns of local richness and improve the prediction of the effects of land use change based on mean site conditions or land use history. [source]

Dispersal frequency affects local biomass production by controlling local diversity

ECOLOGY LETTERS, Issue 6 2006
Birte Matthiessen
Abstract Dispersal is a major factor regulating the number of coexisting species, but the relationship between species diversity and ecosystem processes has mainly been analysed for communities closed to dispersal. We experimentally investigated how initial local diversity and dispersal frequency affect local diversity and biomass production in open benthic microalgal metacommunities. Final local species richness and local biomass production were strongly influenced by dispersal frequency but not by initial local diversity. Both final local richness and final local biomass showed a hump-shaped pattern with increasing dispersal frequency, with a maximum at intermediate dispersal frequencies. Consequently, final local biomass increased linearly with increasing final richness. We conclude that the general relationship between richness and ecosystem functioning remains valid in open systems, but the maintenance of ecosystem processes significantly depends on the effects of dispersal on species richness and local interactions. [source]

Regional enrichment of local assemblages is robust to variation in local productivity, abiotic gradients, and heterogeneity

ECOLOGY LETTERS, Issue 2 2006
Amy L. Freestone
Abstract Theory predicts that the effects of regional richness on the richness of local communities may depend on the productivity, resource availability, and/or heterogeneity of local sites. Using the wetland plant communities of 50 independent streams as ,regions', we tested whether: (1) local richness in 1-m2 quadrats and 50-m stream segments was positively related to regional richness, even after environmental influences were considered; and (2) the effect of regional richness would interact with the effects of biomass, soil moisture, and/or heterogeneity on local richness. In models that explained up to 88% of variation in local richness, we found that richness at both local scales was positively related to regional richness, and that regional richness did not interact with any of the environmental gradients that also shaped local richness. We conclude that species availability from the regional pool may consistently enrich local communities, even while other constraints on local richness operate. [source]

Predicting the relationship between local and regional species richness from a patch occupancy dynamics model

JOURNAL OF ANIMAL ECOLOGY, Issue 2 2000
B. Hugueny
Summary 1.,A linear relationship between the number of species in ecological communities (local richness) and the species pools from which the communities are drawn (regional richness) suggests that species interactions are not sufficient to limit local richness and that communities are not saturated with species. Instead, this relationship implies that communities are open to regional influences and are interlinked by dispersal. 2.,Here we show how the linear relationship between local and regional richness in real, noninteractive, assemblages of cynipid gall wasps on California oaks, can be predicted from a simple patch-occupancy model. 3.,One cynipid assemblage has been surveyed for 3 years, allowing for crude estimates of colonization and extinction rates per patch. Using the mainland/island model of patch occupancy dynamics, these rates are combined with the observed number of cynipid species associated with each oak species (regional richness) to predict the expected local species richness in each patch. Assuming that species are independently distributed among localities, the expected variance in species richness among localities is also computed. 4.,The model is then tested on an independent data set. When differences in sampling effort (number of surveyed trees per locality) were accounted for, the regression equation relating observed (n = 41) to predicted local species richness does not differ statistically from the line of perfect agreement. The residuals are also distributed according to the predicted variance. 5.,Although not statistically significant, the variance in local richness appears to be slightly underestimated by the model. One explanation may be that cynipid species display some positive covariance in their distribution among localities, that is, groups of species occur together in given localities more frequently than would be expected by chance. Variance ratio tests identified statistically positive covariance within cynipid assemblages for three oaks species. 6.,The close fit of the model to the data supports the theoretical scenario for noninteractive communities, that the slope of the local,regional richness relationship and patch-occupancy processes are different expressions of the same phenomenon. [source]

The evolutionary species pool hypothesis and patterns of freshwater diatom diversity along a pH gradient

Are local patterns of anthropoid primate diversity related to patterns of diversity at a larger scale?

Dispersal limitation may result in the unimodal productivity-diversity relationship: a new explanation for a general pattern

JOURNAL OF ECOLOGY, Issue 1 2007
MEELIS PÄRTEL
Summary 1Variation in diversity with habitat productivity has long been a central ecological topic. Plant diversity is mostly highest at intermediate productivity, exhibiting the unimodal (so-called ,hump-back') relationship. This relationship has been explained by both evolutionary and ecological processes, but the potential role of dispersal limitation has not been considered. 2We used European flora data to show that dispersal limitation may contribute to the unimodal productivity-diversity relationship. Species were characterized by their habitat productivity preference and dispersal probability (determined by the number of seeds and the presence of a dispersal syndrome). We calculated average relative dispersal probabilities for species assemblages occurring preferentially in different habitat productivity levels. 3At low productivity levels, species without dispersal syndromes predominate (R2 = 0.89), but at high productivity levels, species with a low number of seeds are common (R2 = 0.89). The total relative dispersal probability, combining both the dispersal probabilities attributable to the number of seeds and to the presence of dispersal syndrome, had a unimodal relationship with habitat productivity (R2 = 0.86). Thus, the unimodal productivity-diversity relationship may arise due to the minimal dispersal limitation of local richness in conditions of moderately low productivity. At very low productivity, the lack of dispersal syndromes may limit dispersal. At high productivity, the low number of seeds may limit dispersal. 4Consequently, in conditions where species pool size and biotic interactions do not vary along productivity gradients, the variation in dispersal probabilities with productivity alone can produce unimodal relationships between diversity and productivity. Thus, dispersal limitation may contribute to the observed diversity pattern and ecosystem functioning to a greater extent than usually assumed. [source]

Assessment of sampling approaches for a multi-taxa invertebrate survey in a South African savanna-mosaic ecosystem

AUSTRAL ECOLOGY, Issue 4 2010
S. J. LOVELL
Abstract Invertebrate diversity is seldom included in conservation assessments, primarily because information is lacking. Broad surveys may be too costly, difficult or ineffective. Here we assess a ,shopping basket' approach, targeting 17 taxa using a range of methods. We sampled 43 one-hectare sites stratified within 560 km2 of heterogenous African savanna. We achieved up to 80% sampling completeness for epigaeic fauna, but generally much lower completeness (around 50%) for plant-dwelling and flying taxa. For the former we identified duplication of methods, and for the latter, addition of methods and increased temporal variation rather than effort would improve completeness. Within a taxon, sampling 75% of species present required, on average, about 784 individuals. When considering the local richness, 75% completeness required about 27 individuals per species, but these figures require validation in other areas. About 58 sites were required to achieve 75% sampling completeness, translating to about one site per 10 km2. The percentage of species sampled only in a particular month ranged between 4% and 46%, with greater temporal effects recorded for flying taxa than for epigaeic ones. The trend was similar for species unique to a particular year, with the most extreme case being 67% of the butterfly species sampled one year not previously recorded. We demonstrated and evaluated the feasibility of a simultaneous multi-taxon survey approach to produce data useful for conservation planning and monitoring. We strongly recommend a quantified approach for surveys and inventories, with details such as specific methods decided based on the biome sampled, and taxonomic expertise available for identification. [source]

The ecological value of Eryngium horridum in maintaining biodiversity in subtropical grasslands

AUSTRAL ECOLOGY, Issue 5 2009
ALESSANDRA FIDELIS
Abstract The role of facilitation in the structuring of plant communities has been often demonstrated in environments under high abiotic stress, especially in semi-arid and arid ecosystems and high elevations. Few studies, however, analysed facilitation in systems that are highly productive and rich in species, which are thought to be theoretically unlikely to demonstrate strong effects of facilitation. Here, we investigate the importance of Eryngium horridum, a rosette species, on the maintenance of plant diversity in subtropical grasslands in southern Brazil. We evaluated facilitation in areas under two different types of management: abandonment and grazing. Plots were established in areas with and without individuals of E. horridum and all species were identified and had their cover estimated. The Relative Neighbour Effect index was calculated in order to verify the presence of competition or facilitation. Our results indicated facilitation in both abandoned and in grazed grasslands, but apparently through different mechanisms. In the first case, the plant's architecture opens the canopy and allows more light to reach small forbs in the grass matrix. In the second case, E. horridum appears to protect more palatable species from herbivores. Otherwise considered an obnoxious species, E. horridum plays an important ecological role in subtropical grasslands in southern Brazil by facilitating other species and consequently, increasing local richness. Areas with this rosette species are important sources of diaspores, which are able to colonize new open sites and thus, maintain biodiversity. [source]

Evolution on a shaky piece of Gondwana: is local endemism recent in New Caledonia?

CLADISTICS, Issue 1 2005
Jérôme Murienne
New Caledonia is well known as a hot spot of biodiversity whose origin as a land mass can be traced back to the Gondwanan supercontinent. The local flora and fauna, in addition to being remarkably rich and endemic, comprise many supposedly relictual groups. Does the New Caledonian biota date back to Gondwanan times, building up its richness and endemism over 100 Myr or does it result from recent diversifications after Tertiary geological catastrophic events? Here we use a molecular phylogenetic approach to answer this question with the study of the Neocaledonian cockroach genus Angustonicus belonging to the subfamily Tryonicinae from Australia and New Caledonia. Both geological and molecular dating show that the diversification of this group is less than two million years old, whatever the date of its origin itself. This dating is not consistent with hypotheses of Gondwanan richness and endemism in New Caledonian biota. In other terms, local richness and endemism at the specific level are not necessarily related to an old Gondwanan origin of the Neocaledonian groups. © The Willi Hennig Society 2005. [source]