Despite much scrutiny the relationship between productivity and species richness remains controversial, and there is little agreement about causal processes. We present the results of a survey of 159 productivity-plant species richness (P-PSR) relationships from 131 published studies. We critically assessed each study with respect to experimental design and for the appropriateness of the surrogates used for productivity. We were able to accept only 60 of the reported relationships as robust tests of the P-PSR relationship and a further 18 as robust tests of the biomass species richness relationship. Previous analyses have found that unimodal P-PSR relationships predominate. In contrast, we found that, in studies that used data of continental to global extent, all P-PSR relationships were positive regardless of grain, that almost all were also positive in data sets of regional extent, and that unimodal relationships were not dominant even in studies of fine grain or small spatial extent. Our results differ substantially from previous meta-analyses because previous studies have included a large number of studies that do not meet basic experimental design criteria for objectively testing P-PSR relationships. These results have important implications for theory that attempts to explain species richness patterns. We critically review four dominant theories in light of our results and develop new falsifiable predictions of relationship from these theories at both small and large spatial scales.

Using an appropriately designed and replicated study of a latitudinal influence on rates of evolution, we test the prediction by K. Rohde [(1992) Oikos 65, 514 -527] that the tempo of molecular evolution in the tropics is greater than at higher latitudes. Consistent with this prediction we found tropical plant species had more than twice the rate of molecular evolution as closely related temperate congeners. Rohde's climate-speciation hypothesis constitutes one explanation for the cause of that relationship. This hypothesis suggests that mutagenesis occurs more frequently as productivity and metabolic rates increase toward the equator. More rapid mutagenesis was then proposed as the mechanism that increases evolutionary tempo and rates of speciation. A second possible explanation is that faster rates of molecular evolution result from higher tropical speciation rates However, we targeted common species to limit the influence of genetic drift, and many of the tropical species we used, despite occurring in abundant populations, had much higher rates of molecular evolution. Nonetheless, this issue is not completely resolved by that precaution and requires further examination.latitude ͉ metabolic rate ͉ molecular evolution ͉ mutagenesis ͉ speciation T he decrease in species richness along the continuum from tropical to polar latitudes is perhaps one of the most widely recognized patterns in nature, yet there is no consensus as to a causal mechanism (1, 2). Indeed, since Hutchinson (3) explored a range of possibilities in his 1959 address, ''homage to Santa Rosalia or why are there so many kinds of animals?'', a plethora of competing ideas that attempt to explain the pattern have emerged (4, 5). In 1808, von Humboldt (6) first suggested that energy was key in generating this relationship, and there are now several theories invoking energy as a determinant of diversity (5). These include the climate-speciation hypothesis of Rohde (7). The central element of that hypothesis is the idea that in warmer, more productive environments metabolic rates are higher and that because the rate of mutagenesis is thought to be positively correlated with metabolic rate (8) the tempo of both evolution and speciation is also greater (7). If rate heterogeneity in molecular evolution is controlled by climate it would also suggest that evolution is a spatially ordered phenomenon as was first proposed by Darwin (9). Here, we test the prediction made by Rhode (7) that rates of molecular evolution are faster in the tropics than at higher latitudes. Alternative hypotheses that might also explain faster molecular evolution in the tropics include: first, the concept under nearly neutral theory that faster rates of genetic drift occur in generally smaller tropical populations (10, 11), and second, the concept of more rapid tropical speciation rates themselves produce faster rates of molecular evolution at low latitudes (12).Nucleotide substitution rates have been found to correlate positively with body temperature where phylogenetically disparat...

Aim Global patterns in primary productivity in natural ecosystems are important for interpreting ecological processes and patterns of biodiversity. Net primary productivity (NPP) on land has long been thought to be greatest in tropical forests and to decrease towards the poles. However, it has recently been claimed that the NPP of mid-latitude forests is as great as, or even greater than, that of tropical forests and that ecologically relevant productivity peaks at mid-latitudes. Here we evaluate these hypotheses by testing for relationships between latitude and productivity using a range of forest productivity datasets. Location Global.Methods We apply ordinary least squares regression and t-test analyses to published latitude-productivity data for forests, specifically updated to include an expanded dataset for the previously data-poor tropics, and we evaluate the relationship between the primary productivity of forests and modelled vascular plant species richness.Results Contrary to the recent claims, we found strong support for a negative relationship between latitude and annual NPP of forests with all datasets, and NPP was significantly greater in tropical forests than in temperate forests. Vascular plant richness was positively correlated with NPP.Main conclusions NPP of forests increases towards the equator. Given that species richness also increases towards the equator, and that vascular plant richness correlates with NPP, these results are consistent with recent meta-analyses showing that the relationships between productivity and species richness of both plants and animals in natural ecosystems are predominantly positive. These results are congruent with ecological theories that predict a positive relationship between species richness and productivity, and they indicate that there is no need to explain peaked richness-productivity relationships over broad spatial extents, since they do not appear to exist.

. Bossart conducts teaching and service-related work in the Wildlife and Avian Laboratory and research on avian and marine mammal diseases. One specific focus of his research involves disease diagnosis utilizing traditional pathologic methodology combined with new immunologic and molecular pathologic techniques. He has collaborative research projects with the National Marine Fisheries Service, National Institute of Environmental Health Sciences, and the Miami Museum of Science. Dr. Bossart is specifically concerned about the future of the critically endangered West Indian manatee. This species is endangered largely due to loss of habitat and human-related mortality, primarily the BREVETOXICOSIS IN MANATEES 277and pulmonary edema and hemorrhage were also seen. Consistent microscopic lesions consisted of catarrhal rhjnitis. pu~monary hemorrhage and edema, multiorgan hemosiderosis, and nonsuppurative leptomeningitis. Immunohistochemical staining using a polyclonal primary antibody to brevetoxin (GAB) showed intense positive staining of lymphocytes and macrophages in the lung, liver, and secondary lymphoid tissues. Additionally, lymphocytes and macrophages associated with the inflammatory lesions of the nasal mucosa and meninges were also positive for brevetoxin. These findings implicate brevetoxicosis as a Component of and the likely primary etiology for the epizootic. The data suggest that mortality resulting from brevetoxicosis may not necessarily be acute but may occur after chronic inhalation andor ingestion. Immunohistochemical staining with interleukin-1 -P-converting enzyme showed positive staining with a cellular tropism similar to GAB. This suggests that brevetoxicosis may initiate apoptosis and/or the release of inflammatory mediators that culminate in fatal toxic shock.

Faster rates of microevolution have been recorded for plants and marine foraminifera occupying warmer low latitude environments relative to those occurring at higher latitudes. By contrast, because this rate heterogeneity has been attributed to a relationship between thermal habit and mutagenesis via a body temperature linkage, it has been assumed that microevolution in mammals should not also vary systematically with environmental temperature. However, this assumption has not previously been empirically examined. In this study, we tested for a thermally mediated influence on the tempo of microevolution among mammals using a comprehensive global dataset that included 260 mammal species, from 10 orders and 29 families. In contrast to theoretical predictions, we found that substitution rates in the cytochrome b gene have been substantially faster for species living in warmer latitudes and elevations relative to sister species living in cooler habitats. These results could not be attributed to factors otherwise thought to influence rates of microevolution, such as body mass differentials or genetic drift. Instead, the results indicate that the tempo of microevolution among mammals is either responding directly to the thermal environment or indirectly via an ecological mechanism such as the 'Red Queen' effect.