I've just read about this concept, but I can't find any exact definitions for it. I'm not working in the field of ecology, so could you please help explain this term in brief?
Thank you so much.
Hi Danny, delayed density dependence refers to density-dependent mortality that involves a time lag after the increase in host/prey density and subsequent predator-induced mortality. For example, in souther pine beetles, the populations increases rapidly, but it takes a year for their predators to produce a new generation, so there are cyclical population trends where beetle abundance increases dramatically and then crashes a year later when the predator population catches up. This is also seen in some fish, where small, fast-growing species rapidly reproduce and then crash a year or more later, when larger, slower-growing predators finally start to limit the population of small fish.
For a better explanation, check out Hajek, A.E. 2004. Natural Enemies: An Introduction to Biological Control. Cambridge University Press.
Hi Danny, one of the best empirical examples of which I am aware is this:
Turchin P., Taylor A.D. & Reeve J.D. (1999). Dynamical role of predators in population cycles of a forest insect: an experimental test. Science, 285, 1068-1071.
They use a 5-year experiment of beetle predator exclusion and show delayed density dependence while conclusively rejecting DD without a time lag. It's a very clear example.
Hi Danny, To further confuse the delayed effects of across life stages, density can have both positive and negative outcomes. If density induces competition it can cause culling that removes weak individuals in a population which in turn can result in higher survival of the remaining population in a later life stage (Gosselin, J.and J. Anderson. 2013. "Resource competition induces heterogeneity and can increase cohort survivorship: selection-event duration matters." Oecologia 173(4):1321-1331.). Available on ResearchGate.
In contrast, if density reduces resources without competition such that the entire population is effected then in a later life stage cohort survival may be reduced. (Anderson, J.J., M.C. Gildea, D.W. Williams, and T. Li. 2008. "Linking Growth, Survival, and Heterogeneity through Vitality." The American Naturalist 171(1):E20-E43.). also ResearchGate
Personally, I think that to understand density one needs to understand its effects on the distribution of survival capacity within a population.
Best Regards
Jim
Hi Mark, Daniel and James,
Sorry for my late response. I understand this concept now. Thank you so much for your very clear explanation and helpful links.
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