Habitat complexity, spatial interference, and "minimum risk distribution": a framework for population stability

Floater, Graham J. (2001) Habitat complexity, spatial interference, and "minimum risk distribution": a framework for population stability. Ecological Monographs, 71 3: 447-468. doi:10.1890/0012-9615(2001)071[0447:HCSIAM]2.0.CO;2

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Author Floater, Graham J.
Title Habitat complexity, spatial interference, and "minimum risk distribution": a framework for population stability
Journal name Ecological Monographs   Check publisher's open access policy
ISSN 0012-9615
1557-7015
Publication date 2001-08
Sub-type Critical review of research, literature review, critical commentary
DOI 10.1890/0012-9615(2001)071[0447:HCSIAM]2.0.CO;2
Open Access Status File (Publisher version)
Volume 71
Issue 3
Start page 447
End page 468
Total pages 22
Place of publication Washington, D. C.
Publisher Ecological Society of America
Collection year 2001
Language eng
Abstract In the past century, the debate over whether or not density-dependent factors regulate populations has generally focused on changes in mean population density, ignoring the spatial variance around the mean as unimportant noise. In an attempt to provide a different framework for understanding population dynamics based on individual fitness, this paper discusses the crucial role of spatial variability itself on the stability of insect populations. The advantages of this method are the following: (1) it is founded on evolutionary principles rather than post hoc assumptions; (2) it erects hypotheses that can be tested; and (3) it links disparate ecological schools, including spatial dynamics, behavioral ecology, preference-performance, and plant apparency into an overall framework. At the core of this framework, habitat complexity governs insect spatial variance. which in turn determines population stability. First, the minimum risk distribution (MRD) is defined as the spatial distribution of individuals that results in the minimum number of premature deaths in a population given the distribution of mortality risk in the habitat (and, therefore, leading to maximized population growth). The greater the divergence of actual spatial patterns of individuals from the MRD, the greater the reduction of population growth and size from high, unstable levels. Then, based on extensive data from 29 populations of the processionary caterpillar, Ochrogaster lunifer, four steps are used to test the effect of habitat interference on population growth rates. (1) The costs (increasing the risk of scramble competition) and benefits (decreasing the risk of inverse density-dependent predation) of egg and larval aggregation are quantified. (2) These costs and benefits, along with the distribution of resources, are used to construct the MRD for each habitat. (3) The MRD is used as a benchmark against which the actual spatial pattern of individuals is compared. The degree of divergence of the actual spatial pattern from the MRD is quantified for each of the 29 habitats. (4) Finally, indices of habitat complexity are used to provide highly accurate predictions of spatial divergence from the MRD, showing that habitat interference reduces population growth rates from high, unstable levels. The reason for the divergence appears to be that high levels of background vegetation (vegetation other than host plants) interfere with female host-searching behavior. This leads to a spatial distribution of egg batches with high mortality risk, and therefore lower population growth. Knowledge of the MRD in other species should be a highly effective means of predicting trends in population dynamics. Species with high divergence between their actual spatial distribution and their MRD may display relatively stable dynamics at low population levels. In contrast, species with low divergence should experience high levels of intragenerational population growth leading to frequent habitat-wide outbreaks and unstable dynamics in the long term. Six hypotheses, erected under the framework of spatial interference, are discussed, and future tests are suggested.
Keyword Ecology
Aggregation
Apparency
Habitat Heterogeneity
Herbivory
Ideal Free Distribution
Insects
Lepidoptera
Ochrogaster Lunifer
Performance
Predation
Preference
Spatial Dynamics
Herrich-schaffer Lepidoptera
Caterpillar Ochrogaster-lunifer
Processionary Caterpillar
Phytophagous Insects
Cruciferous Foodplants
Oviposition Preference
Pierid Butterflies
Hemileuca-lucina
Pyralid Moth
Dynamics
Q-Index Code C1

Document type: Journal Article
Sub-type: Critical review of research, literature review, critical commentary
Collection: School of Biological Sciences Publications
 
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Created: Tue, 14 Aug 2007, 16:50:23 EST