%0 Journal Article %J Oikos %D 2002 %T Effect of local and regional processes on plant species richness in tallgrass prairie %A Scott. L. Collins %A Glenn, S.M. %A J. M. Briggs %K tallgrass prairie %X Historically, diversity in a community was often believed to result primarily from local processes, but recent evidence suggests that regional diversity may strongly influence local diversity as well. We used experimental and observational vegetation data from Konza Prairie, Kansas, USA, to determine if: (1) there is a relationship between local and regional richness in tallgrass prairie vegetation; (2) local dominance reduces local species richness; and (3) reducing local dominance increases local and regional species richness. We found a positive relationship between regional and local richness; however, this relationship varied with grazing, topography and fire frequency. The decline in variance explained in the grazed vegetation, in particular, suggested that local processes associated with grazing pressure on the dominant grasses strongly influenced local species richness. Experimental removal of one of the dominant grasses, Andropogon scoparius, from replicate plots resulted in a significant increase in local species richness compared to adjacent reference plots. Overall all sites, species richness was higher in grazed (192 spp.) compared to ungrazed (158 spp.) areas. Across the Konza Prairie landscape, however, there were no significant differences in the frequency distribution of species occurrences, or in the relationship between the number of sites occupied and average abundance in grazed compared to ungrazed areas. Thus, local processes strongly influenced local richness in this tallgrass prairie, but local processes did not produce different landscape-scale patterns in species distribution and abundance. Because richness was enhanced at all spatial scales by reducing the abundance of dominant species, we suggest that species richness in tallgrass prairie results from feedbacks between, and interactions among, processes operating at multiple scales in space and time. %B Oikos %V 99 %P 571 -579 %G eng %M KNZ00821 %R 10.1034/j.1600-0706.2002.12112.x %0 Journal Article %J Ecological Applications %D 1997 %T Effects of organismal and distance scaling on analysis of species distribution and abundance %A Scott. L. Collins %A Glenn, S.M. %X As communities and populations become increasingly fragmented, much theoretical and some empirical research has focused on the dynamics of metapopulations. Many metapopulation models describe dynamics among populations in a region, yet the scale of the region to which different models apply often is undefined. Because the spatial scale is undefined, testing predictions and assumptions of these models is problematic. Our goal is to present two scaling concepts relevant to these models, distance scaling and organismal scaling, and to apply these scaling notions to patterns of species distribution. To determine distance effects, we analyzed patterns of distribution of four taxonomic groups in tallgrass prairie (grasshoppers, small mammals, vascular plants, and breeding birds) at two spatial scales. To asses organismal effects, we held spatial scale constant and we compared patterns of distribution and abundance among these taxonomic groups. Using long—term data from Konza Prairie, Kansas, there were significant differences in the pattern of distribution of grasshoppers, small mammals, vascular plants, and breeding birds within a single spatial scale. The number of core species (species occupying >90% of the sites in a region) of plants and birds was less than the number of satellite species (those occupying <10% of the sites in a region). The opposite was true for grasshoppers and small mammals. All four distribution patterns were significantly nonrandom, but only grasshoppers and small mammals were significantly bimodal at this scale. Plants and birds were unimodal. The patterns of distribution within these taxonomic groups at two spatial scales were significantly different as well. In all cases, the percentage of species in the core group declined, and the percentage of species in the satellite group increased as spatial scale increased. These results demonstrate the difficulty of testing theoretical models with only one taxonomic group at a single spatial scale. One should not accept or reject a model until the spatial domains of organismal and distance scaling have been properly evaluated. As communities and populations become increasingly fragmented, much theoretical and some empirical research has focused on the dynamics of metapopulations. Many metapopulation models describe dynamics among populations in a region, yet the scale of the “region” to which different models apply often is undefined. Because the spatial scale is undefined, testing predictions and assumptions of these models is problematic. Our goal is to present two scaling concepts relevant to these models, distance scaling and organismal scaling, and to apply these scaling notions to patterns of species distribution. To determine distance effects, we analyzed patterns of distribution of four taxonomic groups in tallgrass prairie (grasshoppers, small mammals, vascular plants, and breeding birds) at two spatial scales. To assess organismal effects, we held spatial scale constant and we compared patterns of distribution and abundance among these taxonomic groups. Using long-term data from Konza Prairie, Kansas, there were significant differences in the pattern of distribution of grasshoppers, small mammals, vascular plants, and breeding birds within a single spatial scale. The number of core species (species occupying >90% of the sites in a region) of plants and birds was less than the number of satellite species (those occupying <10% of the sites in a region). The opposite was true for grasshoppers and small mammals. All four distribution patterns were significantly non-random, but only grasshoppers and small mammals were significantly bimodal at this scale. Plants and birds were unimodal. The patterns of distribution within these taxonomic groups at two spatial scales were significantly different as well. In all cases, the percentage of species in the core group declined, and the percentage of species in the satellite group increased as spatial scale increased. These results demonstrate the difficulty of testing theoretical models with only one taxonomic group at a single spatial scale. One should not accept or reject a model until the spatial domains of organismal and distance scaling have been properly evaluated. %B Ecological Applications %V 7 %P 543 -551 %G eng %M KNZ00582 %R 10.1890/1051-0761(1997)007[0543:EOOADS]2.0.CO;2 %0 Journal Article %J New Zealand Journal of Ecology %D 1997 %T Intermediate disturbance and its relationship to within-and between-patch structure %A Scott. L. Collins %A Glenn, S.M. %X The intermediate disturbance hypothesis has been the focus of considerable analysis in terrestrial and aquatic systems. This model predicts that species diversity will be highest at intermediate frequencies of disturbance. Despite numerous theoretical and empirical analyses, the utility of the model is still the subject of intense debate. Rather than developing restrictive time and space constraints on application, we suggest that the model may best be used as a generalizable framework for testing hypotheses in both aquatic and terrestrial systems. In addition, we believe that the model may be applied to both within- and between-patch scales. Finally, we propose an empirical model in which disturbance is an extinction causing event, and post-disturbance succession is modeled based on the dynamics of immigration and extinction. Such a model can incorporate a variety of patterns in species diversity in response to disturbance. %B New Zealand Journal of Ecology %V 21 %P 103 -110 %G eng %U http://www.jstor.org/stable/24054530 %M KNZ00583 %0 Journal Article %J Ecology %D 1995 %T Experimental analysis of intermediate disturbance and initial floristic composition: decoupling cause and effect %A Scott. L. Collins %A Glenn, S.M. %A D.J. Gibson %X The intermediate disturbance hypothesis predicts that richness will be highest in communities with moderate levels of disturbance and at intermediate time spans following disturbance. This model was proposed as a nonequilibrium explanation of species richness in tropical forests and coral reefs. A second model of succession, initial floristic composition, states that nearly all species, including late seral species, are present at the start of succession. This leads to the prediction that richness should be highest immediately following disturbance. We tested these predictions using plant species composition data from two long—term field experiments in North American tallgrass prairie vegetation. In contrast to one prediction of the intermediate disturbance hypothesis, there was a significant monotonic decline in species richness with increasing disturbance frequency, with no evidence of an optimum, in both field experiments. Species composition on an annually burned site was a subset of that of infrequently burned sites. The average number of species per quadrat and the number of grass, forb, and annual species were lowest on annually burned sites compared to unburned sites and sites burned once every 4 yr. The second prediction of the intermediate disturbance hypothesis, however, was supported. Richness reached a maximum at an intermediate time interval since the last disturbance. This contradicts the prediction from the initial floristic composition model of succession. These results also suggest that the two predictions of the intermediate disturbance hypothesis are independent and unrelated. We propose that this may be explained by uncoupling the effects of disturbance as a single, relatively discrete event from system response to disturbance. From this perspective, disturbance becomes an extinction—causing event in these grasslands, where recovery following disturbance is a balance between immigration and extinction. %B Ecology %V 76 %P 486 -492 %G eng %M KNZ00482 %R 10.2307/1941207 %0 Journal Article %J Folia Geobot.Phytotax, Praha %D 1995 %T Fine-scale spatial organization of tallgrass prairie vegetation along a topographic gradient %A Bartha, S. %A Scott. L. Collins %A Glenn, S.M. %A Kertesz, M. %K diversity %K Functional groups %K Grassland community %K information theory %K Konza Prairie %K Scaling %K Spatial associations %X Fine-scale spatial patterns of native tallgrass prairie vegetation were studied on Konza Prairie, Kansas, USA. Three sites, upland, slope, and lowland, were sampled in an ungrazed watershed. Presence of vascular plant species was recorded in two 25.6 m long transects of contiguous 5×5 cm micro-quadrats on each topographic position. Spatial patterns of species and functional groups were analyzed by information theory models ofJuhász-Nagy. Within-community variability of coexistence was expressed by the diversity and spatial dependence of local species combinations. Considerable diversity in the local coexistence of species was found on each site. Upland and hillside communities were richer and more diverse in species combinations than lowland. Spatial scale effected coexistence relationships. The maxima of information theory estimates varied between 15 and 30 cm. There was no trend in the variation of characteristic scales along the topographical gradient. Above 10 m, all sites tended to be homogeneous. The analysis of spatial associations revealed that variability in the local coexistence of species was strongly constrained in all topographic positions. Overall spatial association of species was the lowest on lowland. The characteristic scales of maximum association were between 1.2 m and 3 m at all sites. The maxima of information theory estimates for the functional group-based data appeared at smaller plot sizes than for the species based analyses. Only weak spatial associations were detected among the functional groups indicating that individuals of functional groups coexist well at small scales, and form combinations close to random expectations. The length of transects did not effect the relative associations. Strong positive correlations were found between the number of components (species or functional groups) and the maxima, of information theory models suggesting that richness is a good predictor of within-community coexistence relations. However, there was no relationship between richness and the characteristic scales of community patterns. %B Folia Geobot.Phytotax, Praha %V 30 %P 169 -184 %G eng %M KNZ00473 %R 10.1007/BF02812096 %0 Book Section %B The Changing Prairie %D 1995 %T Grassland ecosystem and landscape dynamics %A Scott. L. Collins %A Glenn, S.M. %E Anthony Joern %E Keeler, K.K. %B The Changing Prairie %I Oxford University Press %P 128 -156 %G eng %M KNZ00483 %0 Journal Article %J Journal of Vegetation Science %D 1993 %T Experimental analysis of patch dynamics in tallgrass prairie plant communities %A Glenn, S.M. %A Scott. L. Collins %K Grassland community %K Patch structure %K Removal experiment %K Schizachyrium scoparium %X Previous research has indicated that patch structure at small spatial scales (<100m2) in tallgrass prairies was defined by a diverse array of infrequent species because dominant species occurred in all samples at this scale. Also, patch structure was not significantly different from that derived from random species associations. Based on these results, we hypothesized that remo val of a dominant species would have no effect on patch structure in these prairies. We tested this hypothesis by removing a dominant grass, Schizachyrium scoparium (Poaceae), from half of each of four 10 m × 10 m study blocks, and comparing differences in patch structure between control and removal halves before and after removal. The minimum resolution in our study was 1 m2. Patches of similar species composition were defined by cluster analysis of presence/absence data and cover data. Patch sizes ranged from 1 to 34 m2. Following the removal of S. scoparium there was an overall increase in the number of species in the removal half of each block compared to pre-treatment levels. However, the number of patch types and number of spatially mapped groups, based on presence/absence or cover data, did not change between control and removal plots after the removal of S. scoparium. This supports the hypothesis that removal of a large, dominant species would have no effect on patch structure at this scale of resolution in these prairies. Thus, patch structure, as defined here, is an emergent property in these grasslands that is not predictable from changes in species composition. This property of stochastic patch structure results from interactions of processes operating at scales both larger and smaller than our scale of resolution. Stochastic models may provide a reasonable approach to modelling small-scale patch dynamics in tallgrass prairie communities. %B Journal of Vegetation Science %V 4 %P 157 -162 %G eng %M KNZ00401 %R 10.2307/3236100 %0 Journal Article %J Journal of Vegetation Science %D 1993 %T The hierarchical continuum concept %A Scott. L. Collins %A Glenn, S.M. %A Roberts, D.W. %K community structure %K Continuum model %K Gradient analysis %K Hierarchical structure %X Two general models have been proposed to explain the structure of the plant community: the community-unit model of Clements and the continuum model of Whittaker and Curtis, the latter based on Gleason's individualistic distribution of species. It is generally assumed that most ecologists now accept the continuum model. Empirical evidence suggests, however, that the continuum in its current form does not fully describe the observed patterns of vegetation along environmental gradients. In this paper, we introduce the hierarchical continuum as a general concept to represent dynamic community structure along regional spatial gradients. The hierarchical continuum is derived from a combination of the individualistic distribution of species, hierarchical assemblage structure, and the core-satellite species hypothesis. The hierarchical continuum concept predicts that the distribution of species across sites in a region will be polymodal, which reflects hierarchical structure, and that the distribution and abundance of species within and between sites will be spatially and temporally dynamic. Regional distribution of plant species in North American tallgrass prairie, southeastern flood-plain hardwood forests, northern upland hardwood forests, and boreal forests were either bimodal or polymodal as predicted by the hierarchical continuum concept. Species in tallgrass prairie were spatially and temporally dynamic with an average turnover of 8–9 species per 50 m2 yr1. In addition, the hierarchical continuum concept predicts the potential for fractal (self-similar) patterns of community structure, and provides a framework for testable hypotheses concerning species distributions along environmental gradients. %B Journal of Vegetation Science %V 4 %P 149 -156 %G eng %M KNZ00393 %R 10.2307/3236099 %0 Journal Article %J Landscape Ecology %D 1992 %T Disturbances in tallgrass prairie: local versus regional effects on community heterogeneity %A Glenn, S.M. %A Scott. L. Collins %A D.J. Gibson %K tallgrass prairie %B Landscape Ecology %V 7 %P 243 -252 %G eng %M KNZ00359 %R 10.1007/BF00131255 %0 Journal Article %J Oikos %D 1992 %T Effects of scale and disturbance on rates of immigration and extinction of species in prairies %A Glenn, S.M. %A Scott. L. Collins %K fire %X

Relationships between local annual immigration and extinction rate of plant species and total species richness were determined from long-term data in permanent plots in tallgrass and shortgrass prairies in Kansas. Combining plots resulted in higher equilibrium numbers of species as predicted from immigration and extinction rates. Immigration and extinction rates also increased with scale. Extinction rates are higher because the regional scale supports more rare species which, in turn, have high probabilities of extinction. We also tested the hypothesis that extinction rates would be higher on burned versus unburned grasslands, and that immigration rates would be higher on grazed versus ungrazed grasslands. Extinction rates were positively correlated with the number of species at a site, and this relationship was not altered by burning or grazing. Immigration rates were variable, but were sometimes positively correlated with growing season precipitation. Immigration rates decreased in years sites were burned. Therefore, after fire, the number of species going locally extinct was still dependent on earlier species richness, but the number of species added to the site was reduced. Variances in immigration and extinction rates were high, therefore, confident predictions regarding the effects of burning or grazing regimes on species richness could not be made. Variance in rates of immigration and extinction results in a range of values within which the equilibrium number of species fluctuates randomly

%B Oikos %V 63 %P 273 -280 %G eng %M KNZ00358 %R http://www.jstor.org/stable/3545388 %0 Journal Article %J Ecology %D 1991 %T Importance of spatial and temporal dynamics in species regional abundance and distribution %A Scott. L. Collins %A Glenn, S.M. %B Ecology %V 72 %P 654 -664 %G eng %M KNZ00312 %R 10.2307/2937205 %0 Journal Article %J The American Midland Naturalist %D 1990 %T A hierarchical analysis of species abundance patterns in grassland vegetation %A Scott. L. Collins %A Glenn, S.M. %B The American Midland Naturalist %V 135 %P 633 -648 %G eng %M KNZ00268 %R http://www.jstor.org/stable/2462027 %0 Journal Article %J Oikos %D 1990 %T Patch structure in tallgrass prairies: dynamics of satellite species %A Glenn, S.M. %A Scott. L. Collins %K tallgrass prairie %X

Space in tallgrass prairie communities is dominated by a few core species. A large number of less abundant, satellite species occupy the remaining space. These satellite species define vegetation patches that vary withinn and between growing seasons. In order to determine if patch structure was random we established five permanent 100-m2 blocks in undisturbed tallgrass prairie in Oklahoma and Kansas. Presence of core and satellite species in each m2 was sampled over one or two growing seasons. Patch types were defined by cluster analysis. Characteristics of patch structure included number of patch types, patch type diversity, patch composition, number of spatial groups, group size, and fractal dimension of the spatial groups. We generated simulated data sets with random species associations, in which we quantified patch structure. Actual patch structure, defined mainly by satellite species, was not significanly different from simulated patch structure, except that simulated patches were more fragmented. Therefore, processes that affect species associations may not be important controls of patch structure of satellite species within the spatial and temporal scale of this analysis. Because there was some degree of spatial autocorrelation in patch structure, dispersal processes may have significant effects on patch structure at this scale. In order to understand grassland community dynamics, we propose that satellite species should be modelled using stochastic models constrained by core species dynamics. This approach may be applicable to any community with major components operating at different hierarchical levels

%B Oikos %V 57 %P 229 -236 %G eng %M KNZ00279 %R 10.2307/3565944