Question: Does resource partitioning among body sizes at local spatial scales account for the distribution of body sizes at all spatial scales? Hypothesis: Processes controlling regional or global patterns of species richness within size classes are scale-dependent, with regional or global patterns being influenced by macroevolutionary processes such as size-biased extinction/speciation and constraints on maximum/ minimum size as opposed to local-scale interactions. Organisms: 297 species of terrestrial and deep-sea gastropods. Sampling sites: 838 terrestrial sites from 10 biogeographic provinces within a 2300 × 2800 km area in eastern North America, and 37 deep-sea sites from three biogeographic provinces at a depth of 196–5042 m in the western North Atlantic Methods: Multiple parametric and non-parametric statistical tests were used to identify the presence of significant deviations between the distribution of individuals and taxa from site to regional scales in both systems. Conclusions: The number of taxa does not always simply reflect the number of individuals across the body size spectrum with deviations becoming more prevalent with increasing spatial scale. Thus, local-scale interactions and resource partitioning alone are insufficient to explain patterns in body size at larger scales.
The human population and economy have grown exponentially and now have impacts on climate, ecosystem processes, and biodiversity far exceeding those of any other species. Like all organisms, humans are subject to natural laws and are limited by energy and other resources. In this article, we use a macro ecological approach to integrate perspectives of physics, ecology, and economics with an analysis of extensive global data to show how energy imposes fundamental constraints on economic growth and development. We demonstrate a positive scaling relationship between per capita energy use and per capita gross domestic product (GDP) both across nations and within nations over time. Other indicators of socioeconomic status and ecological impactare correlated with energy use and GDP. We estimate global energy consumption for alternative future scenarios of population growth and standards of living. Large amounts of energy will be required to fuel economic growth, increase standards of living, and lift developing...
Abstract A noted impact of urbanization is the tendency for biotic homogenization, or the increase of similarity of geographically disparate communities. On the other hand, some urban habitats harbor biodiversity native to their region, a role potentially important in xeric landscapes, with irrigation increasing the coverage and availability of mesic habitats in an otherwise water-limited landscape. We assessed the relative importance of urban yards as agents of biotic homogenization or riparian refugia by characterizing community composition of Tamaulipan thornforest land snail assemblages across a pronounced precipitation gradient in far south Texas, USA. We quantified α- and β-diversity and assessed whether the land snail fauna of urban yards are more similar to each other across a precipitation gradient than they are to their wild counterparts, as well as determined the significance of moisture in driving Tamaulipan thornforest β-diversity, both in terms of turnover (changing species composition) and nestedness (species loss). Sites with both the wild and wet conditions had the highest values of species richness and abundance. Urban land snail communities were significantly homogenized, outweighing the influence of the precipitation gradient. We did not find urban yards served as a refuge for native, moisture-dependent, riparian snails. Our analyses find that turnover, not nestedness, is the largest contributor to β-diversity in these assemblages. Studies of urbanization should address regional spatial scales to quantify how urbanization modifies regional biodiversity arising from background environmental gradients. Such an approach could lead to improved understanding of how large metroplex areas could be used to maintain and even promote biodiversity.
Assessing the spatial distribution of organisms across landscapes is a key step toward determining processes that produce observed patterns. The spatial distribution of an invasive aquatic mollusk, the zebra mussel (Dreissena polymorpha), was examined in two lake-rich areas (Belarus and midwestern United States) with contrasting invasion histories. Spatial distribution patterns of invaded lakes were determined using Ripley's K. Aggregation of invaded lakes was found at similar spatial extents (<50 km) in both regions; segregation was found at spatial extents >120 km in Belarus. The observed spatial extent of aggregation likely reflected the scale of secondary geographic spread, whereas the scale of long-distance dispersal events was reflected by the spatial extent of segregation. Isolated Belarus lakes were less likely to be invaded than those connected by waterways. Although one-dimensional aggregation of invaded lakes along connected Belarus waterways was not observed, nearest neighbor analysis indicated that zebra mussel dispersal occurred at distances <15 km within these waterways. Based on observed spatial pattern, we concluded that zebra mussels have not yet saturated European and North American lake landscapes, including many suitable lakes. Similar distribution patterns of invaded lakes in Belarus and North America suggest that similar processes have influenced zebra mussel spread in both landscapes.
We examine a novel mathematical approach which posits that the decay of similarity in community composition with increasing distance (aka distance decay) can be modeled as the sum of individual species joint‐probability vs distance relationships. Our model, supported by analyses of these curves from three datasets (North American breeding birds, North American taiga plants, and tropical forest trees), suggest that when sampling grain is large enough to avoid absences due to stochastic sampling effects, and/or sampling extent is large enough to generate species turnover through the deterministic crossing of environmental and/or geographical range limits, species joint‐probability over increasing distance will generally exhibit exponential decay. However, at small scales where occurrence is driven more by stochastic sampling effects, species joint‐probability curves exhibit a power‐law decay form. Lacking a theoretical prediction of how individual species joint‐probability relationships combine to generate community distance decay, we also performed a meta‐analysis of 26 ecological and 4 human‐system datasets, using non‐linear regression to mean and quantile non‐linear regression at tau = 0.95 for linear, exponential, and power‐law decay forms. These analyses demonstrate that the functional form of community distance decay – as shown by comparison of AIC ranks – is largely determined by observational scale, with power law decay prevailing within domains where the species pool remains constant, while exponential decay prevails at larger scales over which the species pool varies, paralleling the patterns predicted in our mathematical approach.
Abstract Issue Lot accession information from natural history collections represents a potentially vital source of large datasets to test biodiversity, biogeography and macroecology hypotheses. But does such information provide an accurate portrayal of the natural world? We review the many types of bias and error intrinsic to museum collection data and consider how these factors may affect their ability to accurately test ecological hypotheses. Evidence We considered all Texas land snail collections from the two major repositories in the state and compared them with an ecological sample drawn across the same landscape. We found that museum collection localities were biased in favour of regions with higher human population densities and iconic destinations. They also tended to be made during attractive temporal windows. Small, uncharismatic taxa tended to be under‐collected while larger, charismatic species were over‐collected. As a result, for most species it was impossible to use museum lot frequency to accurately predict frequency and abundance in an ecological sample. Species misidentification rate was approximately 20%, while 4% of lots represented more than one species. Errors were spread across the entire shell size spectrum and were present in 75% of taxonomic families. Contingency table analysis documented significant dependence of both misidentification and mixed lot rates upon shell size and family richness. Conclusion Researchers should limit their use of museum record data to situations where their inherent biases and errors are irrelevant, rectifiable or explicitly considered. At the same time museums should begin incorporating expert specimen verification into their digitization programs.
