When can nuisance and invasive species control efforts backfire

Department of Natural Resources, Cornell University, Ithaca, New York 14853, USA.
Ecological Applications (Impact Factor: 4.09). 09/2009; 19(6):1585-95. DOI: 10.1890/08-1467.1
Source: PubMed


Population control through harvest has the potential to reduce the abundance of nuisance and invasive species. However, demographic structure and density-dependent processes can confound removal efforts and lead to undesirable consequences, such as overcompensation (an increase in abundance in response to harvest) and instability (population cycling or chaos). Recent empirical studies have demonstrated the potential for increased mortality (such as that caused by harvest) to lead to overcompensation and instability in plant, insect, and fish populations. We developed a general population model with juvenile and adult stages to help determine the conditions under which control harvest efforts can produce unintended outcomes. Analytical and simulation analyses of the model demonstrated that the potential for overcompensation as a result of harvest was significant for species with high fecundity, even when annual stage-specific survivorship values were fairly low. Population instability as a result of harvest occurred less frequently and was only possible with harvest strategies that targeted adults when both fecundity and adult survivorship were high. We considered these results in conjunction with current literature on nuisance and invasive species to propose general guidelines for assessing the risks associated with control harvest based on life history characteristics of target populations. Our results suggest that species with high per capita fecundity (over discrete breeding periods), short juvenile stages, and fairly constant survivorship rates are most likely to respond undesirably to harvest. It is difficult to determine the extent to which overcompensation and instability could occur during real-world removal efforts, and more empirical removal studies should be undertaken to evaluate population-level responses to control harvests. Nevertheless, our results identify key issues that have been seldom acknowledged and are potentially generic across taxa.

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Available from: Elise F Zipkin, Feb 26, 2015
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    • "v with high per capita recruitment rates in which harvest elicits a strong increase in abundance when maturation rates are fixed (Zipkin et al. 2009). However, the dampening of overcompensation by density-dependent maturation does not occur universally—for example, even strong plasticity may have little effect when removal efforts target adults, a common strategy in population control (Brooks and Lebreton 2001), or when competition among juveniles limits maturation (Fig. 2D). "
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    ABSTRACT: Induced changes in the demographic traits of harvested populations produce ecological responses to mortality that are not generally predicted by traditional models. Strong plasticity in maturation rates - commonly observed among intensely harvested populations - varies the time between birth and reproduction of an individual, thereby affecting a population's growth rate. We developed a general model to explore how density-dependent maturation rates affect both population persistence and overcompensation, the situation in which population abundance increases in response to harvest. We find that plasticity in maturation rates generally dampens or eliminates overcompensation in populations. However stage-specific harvest strategies, rather than those that target a population evenly, could elicit or strengthen an overcompensatory response. Therefore, occurrence of overcompensation in a species may be context-dependent. Our results also demonstrate that faster maturation in response to harvest allows populations with low juvenile survival to persist under much greater harvest pressures and maintain higher levels of adult abundance than when maturation rates are not plastic. Strong compensatory responses in age at maturity can greatly amplify the harvest effort required to reduce or collapse populations with low survival rates. Accounting for this effect can be critical to invasive species control or eradication, as well as to the conservation of ecologically and/or economically important populations.
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    • "For example, if we think of α i as the natural survival rates then the population model (3) is a special case of (46). If we allow α i to include additional factors such as harvesting rates then (46) is an extension of the model in [38] (with a Beverton-Holt recruitment function) in the sense that the competition coefficients β i,n , γ i,n , c i,n may be nonzero as well as time-dependent. "
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    ABSTRACT: We study a general discrete planar system for modeling stage-structured populations. Our results include conditions for the global convergence of orbits to zero (extinction) when the parameters (vital rates) are time and density dependent. When the parameters are periodic we obtain weaker conditions for extinction. We also study a rational special case of the system for Beverton-Holt type interactions and show that the persistence equilibrium (in the positive quadrant) may be globally attracting even in the presence of interstage competition. However, we determine that with a sufficiently high level of competition, the persistence equilibrium becomes unstable (a saddle point) and the system exhibits period two oscillations.
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    • "The system (31)-(32) with c 2,n = 0 has been studied in the literature; for instance, an autonomous version is discussed in [6] and [11]. The assumption c 2,n > 0, which adds greater interspecies competition into the stage-structured model, leads to theoretical issues that are not wellunderstood . "
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    ABSTRACT: We study the dynamics of a second-order difference equation that is derived from a planar Ricker model of two-stage (e.g. adult, juvenile) biological populations. We obtain sufficient conditions for global convergence to zero in the non-autonomous case. This gives general conditions for extinction in the biological context. We also study the dynamics of an autonomous special case of the equation that generates multistable periodic and non-periodic orbits in the positive quadrant of the plane.
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