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Trees wanted--dead or alive! Host selection and population dynamics in tree-killing bark beetles.

Kausrud KL, Grégoire JC, Skarpaas O, Erbilgin N, Gilbert M, Økland B, Stenseth NC - PLoS ONE (2011)

Bottom Line: When their population densities are high, some species aggregate on healthy host trees so that their defences may be exhausted and the inner bark successfully colonized, killing the tree in the process.The population dynamics emerging from individual behavior are complex, capable of switching between "endemic" and "epidemic" regimes spontaneously or following changes in host availability or resistance.Model predictions are compared to empirical observations, and we identify some factors determining the occurrence and self-limitation of epidemics.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Centre for Ecological and Evolutionary Synthesis, University of Oslo, Oslo, Norway.

ABSTRACT
Bark beetles (Coleoptera: Curculionidae, Scolytinae) feed and breed in dead or severely weakened host trees. When their population densities are high, some species aggregate on healthy host trees so that their defences may be exhausted and the inner bark successfully colonized, killing the tree in the process. Here we investigate under what conditions participating with unrelated conspecifics in risky mass attacks on living trees is an adaptive strategy, and what this can tell us about bark beetle outbreak dynamics. We find that the outcome of individual host selection may deviate from the ideal free distribution in a way that facilitates the emergence of tree-killing (aggressive) behavior, and that any heritability on traits governing aggressiveness seems likely to exist in a state of flux or cycles consistent with variability observed in natural populations. This may have implications for how economically and ecologically important species respond to environmental changes in climate and landscape (forest) structure. The population dynamics emerging from individual behavior are complex, capable of switching between "endemic" and "epidemic" regimes spontaneously or following changes in host availability or resistance. Model predictions are compared to empirical observations, and we identify some factors determining the occurrence and self-limitation of epidemics.

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Comparisons with other model formulations.a) Comparing the offspring density for the model (red) with an                            established resource-based bark beetle model by Økland and                            Bjørnstad (2006), see Analysis section (blue lines, upper line scaled for better                            fit). The dotted blue line is the population model presented here, but                            with the simplification that living trees are colonised immediately when                            N>T, as is implicit in most current population models that do not                            take adaptive behaviour into account. b) Swarm density for                            which colonizing living trees has a 50% chance of success, as a                            function of colonization threshold (T) and dead trees present                                (Kd). The interaction is strongly non-linear.
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pone-0018274-g006: Comparisons with other model formulations.a) Comparing the offspring density for the model (red) with an established resource-based bark beetle model by Økland and Bjørnstad (2006), see Analysis section (blue lines, upper line scaled for better fit). The dotted blue line is the population model presented here, but with the simplification that living trees are colonised immediately when N>T, as is implicit in most current population models that do not take adaptive behaviour into account. b) Swarm density for which colonizing living trees has a 50% chance of success, as a function of colonization threshold (T) and dead trees present (Kd). The interaction is strongly non-linear.

Mentions: The assumption implicit in some population models that beetles colonize trees to produce new resources when possible (i.e., whenever N>T) creates considerable discrepancies with the SRD, both with respect to densities at which a population can enter an epidemic phase, and to how stable the epidemic can be (Fig. 6).


Trees wanted--dead or alive! Host selection and population dynamics in tree-killing bark beetles.

Kausrud KL, Grégoire JC, Skarpaas O, Erbilgin N, Gilbert M, Økland B, Stenseth NC - PLoS ONE (2011)

Comparisons with other model formulations.a) Comparing the offspring density for the model (red) with an                            established resource-based bark beetle model by Økland and                            Bjørnstad (2006), see Analysis section (blue lines, upper line scaled for better                            fit). The dotted blue line is the population model presented here, but                            with the simplification that living trees are colonised immediately when                            N>T, as is implicit in most current population models that do not                            take adaptive behaviour into account. b) Swarm density for                            which colonizing living trees has a 50% chance of success, as a                            function of colonization threshold (T) and dead trees present                                (Kd). The interaction is strongly non-linear.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3102062&req=5

pone-0018274-g006: Comparisons with other model formulations.a) Comparing the offspring density for the model (red) with an established resource-based bark beetle model by Økland and Bjørnstad (2006), see Analysis section (blue lines, upper line scaled for better fit). The dotted blue line is the population model presented here, but with the simplification that living trees are colonised immediately when N>T, as is implicit in most current population models that do not take adaptive behaviour into account. b) Swarm density for which colonizing living trees has a 50% chance of success, as a function of colonization threshold (T) and dead trees present (Kd). The interaction is strongly non-linear.
Mentions: The assumption implicit in some population models that beetles colonize trees to produce new resources when possible (i.e., whenever N>T) creates considerable discrepancies with the SRD, both with respect to densities at which a population can enter an epidemic phase, and to how stable the epidemic can be (Fig. 6).

Bottom Line: When their population densities are high, some species aggregate on healthy host trees so that their defences may be exhausted and the inner bark successfully colonized, killing the tree in the process.The population dynamics emerging from individual behavior are complex, capable of switching between "endemic" and "epidemic" regimes spontaneously or following changes in host availability or resistance.Model predictions are compared to empirical observations, and we identify some factors determining the occurrence and self-limitation of epidemics.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Centre for Ecological and Evolutionary Synthesis, University of Oslo, Oslo, Norway.

ABSTRACT
Bark beetles (Coleoptera: Curculionidae, Scolytinae) feed and breed in dead or severely weakened host trees. When their population densities are high, some species aggregate on healthy host trees so that their defences may be exhausted and the inner bark successfully colonized, killing the tree in the process. Here we investigate under what conditions participating with unrelated conspecifics in risky mass attacks on living trees is an adaptive strategy, and what this can tell us about bark beetle outbreak dynamics. We find that the outcome of individual host selection may deviate from the ideal free distribution in a way that facilitates the emergence of tree-killing (aggressive) behavior, and that any heritability on traits governing aggressiveness seems likely to exist in a state of flux or cycles consistent with variability observed in natural populations. This may have implications for how economically and ecologically important species respond to environmental changes in climate and landscape (forest) structure. The population dynamics emerging from individual behavior are complex, capable of switching between "endemic" and "epidemic" regimes spontaneously or following changes in host availability or resistance. Model predictions are compared to empirical observations, and we identify some factors determining the occurrence and self-limitation of epidemics.

Show MeSH
Related in: MedlinePlus