Testing Models of Source-Sink Dynamics and Balanced Dispersal

Diffendorfer, James E.

doi:10.2307/3546763

Cited by 225 publications

(227 citation statements)

References 46 publications

(79 reference statements)

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“…By contrast, species that emigrate at lower densities in response to social phenomena such as mate-finding difficulties or reduced predator vigilance (e.g. plants, insects and mammals; Lamont et al 1993;Herzig 1995;Wolff 1997;Diffendorfer 1998;Kuussaari et al 1998) should experience a decrease in diversity in communities that are linked by dispersal compared with isolated ones. Similarly, species engaged in pure pre-emptive competition should be more susceptible to reductions in diversity as a result of perturbations that reduce spatial variation or increase emigration compared with species engaged in dominance competition or asymmetric pre-emption.…”

Section: Discussionmentioning

confidence: 99%

“…Examples include insects (Herzig 1995;Kuussaari et al 1998), birds (Birkhead 1977) and mammals (Wolff 1997;Diffendorfer 1998). When s Ͼ 0, emigration increases with density at an accelerating rate, akin to a Type III functional response at low resource abundances (Murdoch & Oaten 1975 (Denno & Peterson 1995;Fonseca & Hart 1996;Rhainds et al 1998) and territorial birds and mammals (Veit & Lewis 1996;Wolff 1997;Aars & Ims 2000).…”

Section: The Modelmentioning

confidence: 99%

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Spatial variation and density-dependent dispersal in competitive coexistence

Amarasekare

2004

Proc. R. Soc. Lond. B

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It is well known that dispersal from localities favourable to a species' growth and reproduction (sources) can prevent competitive exclusion in unfavourable localities (sinks). What is perhaps less well known is that too much emigration can undermine the viability of sources and cause regional competitive exclusion. Here, I investigate two biological mechanisms that reduce the cost of dispersal to source communities. The first involves increasing the spatial variation in the strength of competition such that sources can withstand high rates of emigration; the second involves reducing emigration from sources via density-dependent dispersal. I compare how different forms of spatial variation and modes of dispersal influence source viability, and hence source-sink coexistence, under dominance and pre-emptive competition. A key finding is that, while spatial variation substantially reduces dispersal costs under both types of competition, density-dependent dispersal does so only under dominance competition. For instance, when spatial variation in the strength of competition is high, coexistence is possible (regardless of the type of competition) even when sources experience high emigration rates; when spatial variation is low, coexistence is restricted even under low emigration rates. Under dominance competition, density-dependent dispersal has a strong effect on coexistence. For instance, when the emigration rate increases with density at an accelerating rate (Type III densitydependent dispersal), coexistence is possible even when spatial variation is quite low; when the emigration rate increases with density at a decelerating rate (Type II density-dependent dispersal), coexistence is restricted even when spatial variation is quite high. Under pre-emptive competition, density-dependent dispersal has only a marginal effect on coexistence. Thus, the diversity-reducing effects of high dispersal rates persist under pre-emptive competition even when dispersal is density dependent, but can be significantly mitigated under dominance competition if density-dependent dispersal is Type III rather than Type II. These results lead to testable predictions about source-sink coexistence under different regimes of competition, spatial variation and dispersal. They identify situations in which density-independent dispersal provides a reasonable approximation to species' dispersal patterns, and those under which consideration of density-dependent dispersal is crucial to predicting long-term coexistence.

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Section: Discussionmentioning

confidence: 99%

Section: The Modelmentioning

confidence: 99%

Spatial variation and density-dependent dispersal in competitive coexistence

Amarasekare

2004

Proc. R. Soc. Lond. B

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“…Yet this assumption is rarely likely to be true in nature. Evidence from some systems indicates that the proportion of dispersers from a given habitat may be in versely related to conspecific density or affected by dif ferences in habitat condition so that individuals disperse to and away from sites proportionally to achieve an ideal free distribution (Doncaster et al 1997;Diffendorfer 1998;Haugen et al 2006). Our review suggests that patch en vironment can affect the development of connectivity be tween local sites by generating repeatable differences be tween types of patches and the probability that individuals leave their natal patch.…”

Section: Ecological Implicationsmentioning

confidence: 99%

Integrating across Life-History Stages: Consequences of Natal Habitat Effects on Dispersal

Benard¹,

McCauley²

2008

The American Naturalist

125

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Ecological and evolutionary processes are affected by forces acting at both local and regional scales, yet our understanding of how these scales interact has remained limited. These processes are fundamentally linked through individuals that develop as juve niles in one environment and then either remain in the natal habitat or disperse to new environments. Empirical studies in a diverse range of organisms have demonstrated that the conditions experienced in the natal habitat can have profound effects on the adult phenotype. This environmentally induced phenotypic variation can in turn affect the probability that an individual will disperse to a new environment and the ecological and evolutionary impact of that individual in the new environment. We synthesize the literature on this process and propose a framework for exploring the linkage between local devel opmental environment and dispersal. We then discuss the ecological and evolutionary implications of dispersal asymmetries generated by the effects of natal habitat conditions on individual phenotypes. Our review indicates that the influence of natal habitat conditions on adult phenotypes may be a highly general mechanism affecting the flow of individuals between populations. The wealth of information already gathered on how local conditions affect adult phenotype can and should be integrated into the study of dispersal as a critical force in ecology and evolution.

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“…Data, however, show that dispersal rate can both increase and decrease with increasing density (e.g. Denno & Peterson 1995;Herzig 1995;Fonseca & Hart 1996;Veit & Lewis 1996;Doncaster et al 1997;Wolff 1997;Diffendorfer 1998;Aars & Ims 2000). Data also show that species engage in both dominance and pre-emptive competition, as well as combinations thereof.…”

Section: Introductionmentioning

confidence: 99%

Spatial Heterogeneity, Source‐Sink Dynamics, and the Local Coexistence of Competing Species

Amarasekare¹,

Nisbet²

2001

The American Naturalist

316

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Patch occupancy theory predicts that a trade-off between competition and dispersal should lead to regional coexistence of competing species. Empirical investigations, however, find local coexistence of superior and inferior competitors, an outcome that cannot be explained within the patch occupancy framework because of the decoupling of local and spatial dynamics. We develop two-patch metapopulation models that explicitly consider the interaction between competition and dispersal. We show that a dispersal-competition trade-off can lead to local coexistence provided the inferior competitor is superior at colonizing empty patches as well as immigrating among occupied patches. Immigration from patches that the superior competitor cannot colonize rescues the inferior competitor from extinction in patches that both species colonize. Too much immigration, however, can be detrimental to coexistence. When competitive asymmetry between species is high, local coexistence is possible only if the dispersal rate of the inferior competitor occurs below a critical threshold. If competing species have comparable colonization abilities and the environment is otherwise spatially homogeneous, a superior ability to immigrate among occupied patches cannot prevent exclusion of the inferior competitor. If, however, biotic or abiotic factors create spatial heterogeneity in competitive rankings across the landscape, local coexistence can occur even in the absence of a dispersal-competition trade-off. In fact, coexistence requires that the dispersal rate of the overall inferior competitor not exceed a critical threshold. Explicit consideration of how dispersal modifies local competitive interactions shifts the focus from the patch occupancy approach with its emphasis on extinctioncolonization dynamics to the realm of source-sink dynamics. The key to coexistence in this framework is spatial variance in fitness. Unlike in the patch occupancy framework, high rates of dispersal * Present address: Department of Ecology and Evolution, University of Chicago, Chicago, Illinois 60637-1573; e-mail: amarasek@uchicago.edu. † E-mail: nisbet@lifesci.ucsb.edu.Am. Nat. 2001. Vol. 158, pp. 572- can undermine coexistence, and hence diversity, by reducing spatial variance in fitness.Keywords: competition, coexistence, spatial heterogeneity, source-sink dynamics, immigration, dispersal-competition trade-off.The issue of how species coexist in patchy environments is central to both basic and applied ecology. When competition for resources is asymmetric, a life-history tradeoff between competitive and dispersal abilities can lead to coexistence in a patchy environment (Skellem 1951). This idea has been formalized in the patch occupancy metapopulation framework (Levins 1969(Levins , 1970. The patch occupancy approach assumes that local competitive interactions occur on a much faster time scale relative to extinction-colonization dynamics (Cohen 1970;Levins and Culver 1971;Slatkin 1974;Hastings 1980;Nee and May 1992;Tilman et al. 1994). For instance,...

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Testing Models of Source-Sink Dynamics and Balanced Dispersal

Cited by 225 publications

References 46 publications

Spatial variation and density-dependent dispersal in competitive coexistence

Spatial variation and density-dependent dispersal in competitive coexistence

Integrating across Life-History Stages: Consequences of Natal Habitat Effects on Dispersal

Spatial Heterogeneity, Source‐Sink Dynamics, and the Local Coexistence of Competing Species

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