The response of avian predator populations to forest tent caterpillar (Malacosoma disstria; Lepidoptera: Lasiocampidae) outbreaks in Ontario, Canada

Outbreaks of insect defoliators have broad ecological effects on forested ecosystems because they can cause extensive mortality in host tree populations. They also represent peaks in the density of food for specialist and generalist predators, and some species of insectivorous birds show strong responses to outbreaks of defoliators. Using over 50 years of bird counts and defoliation data, I examined the response of four species with a range of foraging specializations to outbreaks of the forest tent caterpillar, a major defoliator of deciduous trees in eastern North America. The specialist blackbilled cuckoo (Coccyzus erythropthalmus) showed strong aggregative and numerical responses to the outbreaks of forest tent caterpillar at local and regional spatial scales, respectively. In contrast, species with a lower degree of foraging specialization, the least flycatcher (Empidonax minimus), the yellow warbler (Setophaga petechia), and the black-capped chickadee (Poecile atricapillus) showed weak or null aggregational and numerical responses to the outbreaks, suggesting that they forage opportunistically on forest tent caterpillars and that this does not result in increased reproductive output. The results of this study are consistent with the idea that only species with a high degree of foraging specialization can take advantage of a food resource that fluctuates in a predictable manner, and highlights the need to consider the predator-prey dynamics when managing population outbreaks of insect defoliators

Concurrent habitat and life history influences on effective/census population size ratios in stream-dwelling trout

Lower effective sizes (Ne) than census sizes (N) are routinely documented in natural populations, but knowledge of how multiple factors interact to lower Ne/N ratios is often limited. We show how combined habitat and life-history influences drive a 2.4- to 6.1-fold difference in Ne/N ratios between two pristine brook trout (Salvelinus fontinalis) populations occupying streams separated by only 750 m. Local habitat features, particularly drainage area and stream depth, govern trout biomass produced in each stream. They also generate higher trout densities in the shallower stream by favoring smaller body size and earlier age-at-maturity. The combination of higher densities and reduced breeding site availability in the shallower stream likely leads to more competition among breeding trout, which results in greater variance in individual reproductive success and a greater reduction in Ne relative to N. A similar disparity between juvenile or adult densities and breeding habitat availability is reported for other species and hence may also result in divergent Ne/N ratios elsewhere. These divergent Ne/N ratios between adjacent populations are also an instructive reminder for species conservation programs that genetic and demographic parameters may differ dramatically within species

Appendix E. Pairwise θST estimates between each cohort from all study populations estimated using GENETIX 4.0.

Pairwise θST estimates between each cohort from all study populations estimated using GENETIX 4.0

Appendix G. Variable hypothesis: habitat parameter means vs. N and Nb in 2010 and 2011.

Variable hypothesis: habitat parameter means vs. N and Nb in 2010 and 2011

Appendix C. Number of breeders (Nb) estimated for each sampled cohort of each population using LDNe.

Number of breeders (Nb) estimated for each sampled cohort of each population using LDNe

Appendix I. Correctly matched Nb/N ratios for 13 populations.

Correctly matched Nb/N ratios for 13 populations

Appendix F. Directional hypothesis: generalized additive model (GAM) plots of habitat parameters vs. N and Nb in 2010 and 2011.

Directional hypothesis: generalized additive model (GAM) plots of habitat parameters vs. N and Nb in 2010 and 2011

Appendix A. Habitat data collection methodology and habitat character estimates for 2010 and 2011.

Habitat data collection methodology and habitat character estimates for 2010 and 2011

Appendix D. Within-population genetic diversity characteristics based on 13 microsatellite loci for all sampled cohorts of each population.

Within-population genetic diversity characteristics based on 13 microsatellite loci for all sampled cohorts of each population

Appendix H. Variable hypothesis: habitat parameter coefficients of variation (CVs) vs. N and Nb in 2010 and 2011.

Variable hypothesis: habitat parameter coefficients of variation (CVs) vs. N and Nb in 2010 and 2011