Fluctuation periodicity,generation separation,and the expression of larval competition

A suite of models has been formulated to investigate the dynamic consequences of the various routes by which uniform larval competition for food can find demographic expression. It is found that while delayed expression through the vital rates of later age classes gives rise to limit cycles containing multiple overlapping generations, immediate expression via changes in the death or growth rates of the larvae themselves leads to self-sustaining single generation limit cycles. When immediate expression of competition is combined with high adult fecundity and short reproductive lifespan the amplitude of the single generation cycles is so large that they constitute a series of evenly spaced discrete generations, which is maintained indefinitely even in the absence of external cues.     

The systematic formulation of population models for insects with dynamically varying instar duration

We develop a formalism for insect population dynamics which covers the situation where maturation from one instar to its successor is triggered by weight gain and not by chronological age. We specify assumptions which result in the instantaneous “subpopulations” of various instars obeying delay-defferential equations with time delays (representing instar duration) which are themselves dynamic variables, changing in response to the availability of food. We demonstrate the stabilizing potential of variable time delays by studying an idealised two-stage model in which maturation to the adult stage occurs after absorption of a given (fixed) quantity of food.     

Conservation genetics of the Common Tern (Sterna hirundo) in the North Atlantic region; implications for the critically endangered population at Bermuda

Common Terns nesting at Bermuda are isolated by 1,000–4,000?km from other populations of the species around the North Atlantic Ocean. This population experienced a severe demographic bottleneck as a result of a hurricane in 2003 and was subsequently re-established by four males and four females. Using seven microsatellite loci, we compared the genetic diversity of the pre- and post-bottleneck populations, compared the genetic profile of the Bermuda population with those of other populations around the North Atlantic Ocean and mainland Europe, and assessed the potential contribution of immigration to genetic diversity. We found a loss of genetic diversity (number of alleles and heterozygosity) in the post-bottleneck Bermudian population (4.6–2.9 and 0.56–0.52, respectively). We also report significant differentiation among all sampled locations (global F_ST?=?0.16) with no evidence for immigration into Bermuda. Common Terns from the Azores were genetically more similar to those from mainland North America than to those from Bermuda or mainland Europe. Our results suggest that the critically endangered population in Bermuda is genetically distinct and requires continued and enhanced conservation priority.