Academic literature on the topic 'Diversity-stability hypothesis'

There are many relationships between ecosystem properties and species (Jones and Lawton, 1995) with the potential links described by five hypotheses: 1. The null hypothesis claims that there is no effect of species diversity on ecosystem processes. The following hypotheses imply biological mechanisms. 2. The diversity–stability hypothesis predicts that ecosystem productivity and recovery increase as the number of species increases (Johnson et al. 1996). 3. The rivet hypothesis predicts a threshold in species richness, below which ecosystem function declines steadily and above which changes in species richness are not reflected by changes in ecosystem function (Ehrlich and Ehrlich 1981; Vitousek and Hooper 1993). 4. The redundant species hypothesis states that species loss has little effect on ecosystem processes if the losses are within the same functional group (Walker 1992) 5. The idiosyncratic response hypothesis suggests that as diversity changes so do ecocosystem processes (Lawton 1994, Lawton and Brown 1994). There have been both field and laboratory attempts to test these hypotheses, (Naeem and Li 1998), however, the interpretation and the generality of the results remain contentious (Tilman 1999). A fundamental reason for such uncertainty is that the hypotheses are not driven by a comprehensive theory of the relationship between species properties and ecosystem processes (Tilman et al., 1997). We propose that the foundations for the necessary theory are in models of the distribution of resources and their utilization by organisms. This is because ecosystem processes such as primary production, decomposition, mineralization, and evapotranspiration are dependent on the processing of resources by the species that are producers, consumers, and decomposers. A theory that links the direct participation of species in ecosystem processes may resolve differences among the various hypotheses or identify how they complement each other. From a community perspective, a theory of resource utilization is based on two alternative assumptions: 1. The rate of ecosystem processes is determined by the few species that are most efficient in using and converting resources. For example, in a desert system, dominant species are those that are proficient in using water for biomass production or in converting inorganic matter into organic materials.

<em>Abstract</em>.—Five conceptual models of longitudinal fish community organization in streams were examined: (1) niche diversity model (NDM), (2) stream continuum model (SCM), (3) immigrant accessibility model (IAM), (4) environmental stability model (ESM), and (5) adventitious stream model (ASM). We used differences among models in their predictions about temporal species turnover, along with five spatiotemporal fish community data sets, to evaluate model applicability. Models were similar in predicting a positive species richness–stream size relationship and longitudinal species nestedness, but differed in predicting either similar temporal species turnover throughout the stream continuum (NDM, SCM), higher turnover upstream (IAM, ESM), or higher turnover downstream (ASM). We calculated measures of spatial and temporal variation from spatiotemporal fish data in five wadeable streams in central and eastern North America spanning 34–68 years (French Creek [New York], Piasa Creek [Illinois], Spruce Run [Virginia], Little Stony Creek [Virginia], and Sinking Creek [Virginia]). All streams exhibited substantial species turnover (i.e., at least 27% turnover in stream-scale species pools), in contrast to the predictions of the SCM. Furthermore, community change was greater in downstream than upstream reaches in four of five streams. This result is most consistent with the ASM and suggests that downstream communities are strongly influenced by migrants to and from species pools outside the focal stream. In Sinking Creek, which is isolated from external species pools, temporal species turnover (via increased richness) was higher upstream than downstream, which is a pattern most consistent with the IAM or ESM. These results corroborate the hypothesis that temperate stream habitats and fish communities are temporally dynamic and that fish migration and environmental disturbances play fundamental roles in stream fish community organization.

<em>Abstract.</em>—We reviewed native fish zoogeography in 22 major tributary basins of the Missouri River basin in the Great Plains geomorphic province and used island biogeographical approaches to study the influence of basin area and isolation on faunal composition. Basin area was correlated with elevation range and basin isolation was negatively correlated with annual freeze-free days. Ninety-six species were native to the tributary basins. Ninety-one were of southern (Gulf of Mexico drainage) origin. Fifty were found in four or fewer tributary basins and, except for three mountain species, were only found from the Cheyenne basin downstream. Twenty-five widespread species were either present among tributary basins during glaciation or colonized the region during recession of the continental glaciers. Sixty-six more restricted species presumably colonized more recently. Five species colonized from Pacific Ocean drainages via interdrainage connections in the Rocky Mountains. The hypothesis that variation between some closely related Great Plains fishes reflects the former presence of a prehistoric “Ancient Plains Drainage” is no longer tenable given recent geological findings, but a series of stream captures between the ancient Arkansas and Kansas basins could account for such variation. All analyses indicated that native fish faunal composition among tributary basins was heavily influenced by factors related to basin area and isolation. A presence–absence matrix of fishes by tributary basin had very high nestedness, whether ordered by basin area or basin isolation. Cluster analysis of Wilcoxon two-sample tests of individual species distributions revealed seven species groups with distinct distribution patterns. The three largest groups were most prevalent in less isolated (southern) tributary basins. A nonmetric multidimensional scaling analysis (NMDS) based on Sørensen’s index of similarity indicated that two axes (both correlated with tributary basin isolation, one correlated with tributary basin area) accounted for 95% of variance between distance in the ordination space and distance in the original <em>n</em>-dimensional space. A cluster analysis of NMDS scores identified five tributary basin groups. The five southernmost basins (Kansas to White) composed one group, and the eight basins to the north (Bad to Little Missouri) composed another. The nine northernmost basins were split into three groups, one including small basins isolated from the Rocky Mountains, another including large basins with Rocky Mountain headwaters, and the last including two basins that were mostly within the Rocky Mountains. The influence of tributary basin area on faunal composition was presumably due to increased chance of colonization, higher habitat stability, and higher habitat diversity in larger tributary basins. The influence of tributary basin isolation was presumably due to higher colonization rates and more equitable climate in southern tributary basins. Fish faunas of the Missouri River basin in the Great Plains have experienced cyclical geomorphic and climatic instability for roughly 2.8 million years and were assembled like island faunas by variable colonization and extinction rates mediated by tributary basin area and isolation. This contrasts with the highly diverse freshwater fish faunas of the Central Highlands that have differentiated through speciation within regions that have been relatively stable geomorphically and climatically for more than 38 million years.