Effects of Organismal and Distance Scaling on Analysis of Species Distribution and Abundance

Collins, Scott L.; Glenn, Susan M.

doi:10.1890/1051-0761(1997)007[0543:eooads]2.0.co;2

Cited by 110 publications

(66 citation statements)

References 46 publications

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“…(3) The larger the number of sample sites, the greater the proportion of satellite species and the smaller the proportion of core species (Williams 1950(Williams , 1964. This phenomenon has also been termed ''distance scaling'' by Collins and Glenn (1997) and was first demonstrated by Williams (1950Williams ( , 1964. (4) The presence or absence of bimodality is sensitive to the spatial scale of observation (Williams 1964, Brown 1984.…”

Section: Introductionmentioning

confidence: 82%

Testing Generalities in the Shape of Patch Occupancy Frequency Distributions

Rensburg

McGeoch

Matthews³

et al. 2000

Ecology

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Bimodal patch occupancy frequency distributions regularly appear in studies of a variety of taxa at a variety of spatial scales. Metapopulation models associated with the core-satellite hypothesis and a strong rescue effect predict the occurrence of this bimodality. However, there have been numerous other explanations, both artifactual and biological, of bimodality in patch occupancy frequency distributions. One approach to a better understanding of the phenomenon is to conduct studies on a variety of taxa and spatial scales. Here we examine patterns of patch occupancy frequency distributions for plants, dung beetles, and birds at four spatial scales in sand forest and mixed woodland in Tembe Elephant Park and Sileza Nature Reserve in South Africa. We then examine the predictions of each alternative mechanism proposed to explain bimodality with respect to the patterns found in this study. The incidence of bimodality was high. Little evidence was found for any of the artifactual or nonmetapopulation-based explanations of bimodality. Although there were no between-taxon differences in the shape of occupancy distributions, there was a clear trend of decreasing frequency of bimodality with an increase in the size of the area examined. The general shape of range-size frequency distributions in combination with an area effect is suggested as a mechanism underlying this pattern. Metapopulation dynamics associated with a strong rescue effect could also not be excluded as a possible mechanism playing a role in generating the bimodality found at the patch scale.

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Section: Introductionmentioning

confidence: 82%

Testing Generalities in the Shape of Patch Occupancy Frequency Distributions

Rensburg

McGeoch

Matthews³

et al. 2000

Ecology

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“…Most exclosures are subjectively located near roads and in flat terrain. Local species richness, for example, may be poorly correlated with landscapescale species richness, because species overlap and species richness are highly dependent on scale (e.g., Collins and Glenn 1997, Stohlgren et al 1997a, 1999. None of the studies that we reviewed detailed the sample population (i.e., all potential sites from which the exclosure sites were selected).…”

Section: Introductionmentioning

confidence: 99%

How Grazing and Soil Quality Affect Native and Exotic Plant Diversity in Rocky Mountain Grasslands

Stohlgren

Schell

Heuvel

1999

Ecological Applications

298

142

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We used multiscale plots to sample vascular plant diversity and soil characteristics in and adjacent to 26 long-term grazing exclosure sites in Colorado, Wyoming, Montana, and South Dakota, USA. The exclosures were 7-60 yr old (31.2 Ϯ 2.5 yr, mean Ϯ 1 SE). Plots were also randomly placed in the broader landscape in open rangeland in the same vegetation type at each site to assess spatial variation in grazed landscapes. Consistent sampling in the nine National Parks, Wildlife Refuges, and other management units yielded data from 78 1000-m 2 plots and 780 1-m 2 subplots. We hypothesized that native species richness would be lower in the exclosures than in grazed sites, due to competitive exclusion in the absence of grazing. We also hypothesized that grazed sites would have higher native and exotic species richness compared to ungrazed areas, due to disturbance (i.e., the intermediate-disturbance hypothesis) and the conventional wisdom that grazing may accelerate weed invasion. Both hypotheses were soundly rejected. Although native species richness in 1-m 2 subplots was significantly higher (P Ͻ 0.05) in grazed sites, we found nearly identical native or exotic species richness in 1000-m 2 plots in exclosures (31.5 Ϯ 2.5 native and 3.1 Ϯ 0.5 exotic species), adjacent grazed plots (32.6 Ϯ 2.8 native and 3.2 Ϯ 0.6 exotic species), and randomly selected grazed plots (31.6 Ϯ 2.9 native and 3.2 Ϯ 0.6 exotic species). We found no significant differences in species diversity (Hill's diversity indices, N1 and N2), evenness (Hill's ratio of evenness, E5), cover of various life-forms (grasses, forbs, and shrubs), soil texture, or soil percentage of N and C between grazed and ungrazed sites at the 1000-m 2 plot scale. The species lists of the long-ungrazed and adjacent grazed plots overlapped just 57.9 Ϯ 2.8%. This difference in species composition is commonly attributed solely to the difference in grazing regimes. However, the species lists between pairs of grazed plots (adjacent and distant 1000-m 2 plots) in the same vegetation type overlapped just 48.6 Ϯ 3.6%, and the ungrazed plots and distant grazed plots overlapped 49.4 Ϯ 3.6%. Differences in vegetation and soils between grazed and ungrazed sites were minimal in most cases, but soil characteristics and elevation were strongly correlated with native and exotic plant diversity in the study region. For the 78 1000-m 2 plots, 59.4% of the variance in total species richness was explained by percentage of silt (coefficient ϭ 0.647, t ϭ 5.107, P Ͻ 0.001), elevation (coefficient ϭ 0.012, t ϭ 5.084, P Ͻ 0.001), and total foliar cover (coefficient ϭ 0.110, t ϭ 2.104, P Ͻ 0.039). Only 12.8% of the variance in exotic species cover (log 10 cover) was explained by percentage of clay (coefficient ϭ Ϫ0.011, t ϭ Ϫ2.878, P Ͻ 0.005), native species richness (coefficient ϭ Ϫ0.011, t ϭ Ϫ2.156, P Ͻ 0.034), and log 10 N (coefficient ϭ 2.827, t ϭ 1.860, P Ͻ 0.067). Native species cover and exotic species richness and frequency were also significantly positively correlated with percentage of soi...

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“…One reason that we are resistant to employing a metapopulation or refuge model is that although the assumptions and conditions of the model may hold for some species, they may not hold for all species (see Collins and Glenn 1997). We suspect that because of the extremely heterogeneous nature of the scrub habitat (see Myers 1990), many scrub vertebrates have dealt successfully with habitat fragmentation throughout much of their evolutionary histories (see Jackson 1973, Campbell andChristman 1982), and can, on the one hand, resist extinction at what seem to the observer to be very low population sizes and, on the other hand, disperse between habitat fragments that seem to the observer to be isolated from each other (see Harrison 1989Harrison , 1991.…”

Section: Discussionmentioning

confidence: 99%

Habitat Fragmentation and the Abundances of Vertebrates in the Florida Scrub

McCoy

Mushinsky

1999

Ecology

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JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.. Ecological Society of America is collaborating with JSTOR to digitize, preserve and extend access to Ecology.Abstract. Based on presence/absence of species, we proposed previously that large fragments of the Florida sand pine scrub habitat do not possess greater conservation value for vertebrates than do archipelagos of small and medium-sized fragments. We reexamined the values of fragments of different sizes, based this time on abundances of species. We asked whether abundances tend to decrease with decreasing scrub size or are more strongly related to other scrub attribute(s).We censused vertebrates with trap arrays and by direct observation, and we measured 13 potentially important environmental attributes related to area, isolation, and habitat structure in 16 scrubs distributed along the Lake Wales Ridge of central Florida. We correlated abundance of species with the 13 attributes. We calculated the evenness of relative abundance distributions and grouped scrubs based on the shapes of relative abundance distributions. We determined whether or not members of different groups of scrubs possessed different values for any attribute. Finally, we examined both densities of individuals and dispersions of species among large, medium, and small scrubs.Abundance was related to many of the attributes. Abundances of 11 of 18 species were correlated positively with area. Percentage of variation explained by area generally was low, and several of the rare species apparently maintain relatively large populations in small scrubs. Abundances of five species were correlated negatively with measures of isolation. Abundances of three species were correlated both positively and negatively with measures of habitat structure. Environmental attributes related to isolation and habitat structure were correlated most strongly with both evenness and groupings of relative abundance distributions. Total density of individuals (i.e., numbers of captures per trap array) could not be shown to differ among scrubs of different sizes. Individually, the species that reached their highest densities in relatively small scrubs often were the ones considered to be rare. Spatial distributions of species tended to become more homogeneous as area decreased, but the strength of this effect varied among species, perhaps accounting, at least in part, for the different relationships between abundance and area among species.Our results could lead to broad generalizations that seem to be relevant to scrub conservation. For example, because most species are relatively abundant in large scrubs, large scrubs should be selected for reserves over small ones. We suggest, however, that our results actually best serve as a caution ...

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Effects of Organismal and Distance Scaling on Analysis of Species Distribution and Abundance

Cited by 110 publications

References 46 publications

Testing Generalities in the Shape of Patch Occupancy Frequency Distributions

Testing Generalities in the Shape of Patch Occupancy Frequency Distributions

How Grazing and Soil Quality Affect Native and Exotic Plant Diversity in Rocky Mountain Grasslands

Habitat Fragmentation and the Abundances of Vertebrates in the Florida Scrub

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