More on the department Animal Population Biology

The life-history of animals is the central and unifying theme of research by the Department of Animal Population Biology (APB). Life-history traits comprise the most important characteristics of individuals in relation to their ecology, and are fundamental to any attempt to integrate our understanding of animal ecology on both ecological and evolutionary time scales.

On the one hand, life history variables completely specify the demography and dynamics of populations. On the other, life-history variables either constitute or are directly related to components of fitness, and are susceptible to selection by the abiotic and biotic environment, including the population dynamics of conspecifics and heterospecifics. Understanding this feedback between individual life histories and ecology is therefore crucial to a complete understanding of population ecology, and ultimately also community and ecosystem ecology. We seek to explain variance in trait values as well as the average, and to dissect the relative contributions of phenotypic plasticity (one genotype leads to different phenotypes under different conditions) and genetic differentiation to adaptive variation.

Long history

The Department of Animal Population Biology and its predecessors have a long history of research on life-histories, beginning with Kluijver's research in the 1950's attempting to explain the average clutch size of bird populations as the outcome of natural selection acting on individuals. APB has continued to build on and exploit these strong foundations, by developing new research questions around a central thread. These questions are currently grouped into three areas at the forefront of behavioral and evolutionary ecology:

1. Integration of life-history traits
Early studies of life histories focused on a limited range of variables such as clutch size or laying date. However, the appreciation that trade-offs between different life-history traits are all-pervasive has driven ecologists to consider a wider range of life-history traits and towards a final goal of studying the life-history of organisms as a comprehensive whole. We are attempting to make this link in two directions.

(a) In building from individual traits to the whole life-history, we have broadened the range of life history characters to include reproduction (when to reproduce, how many offspring per reproductive event, the sex and personality of these offspring, how much to invest in rearing these offspring), dispersal (whether to stay in the natal area or to disperse, when to disperse, how far), communication and territoriality (where to settle and how to advertise and defend the territory), migration (when to leave from and when to return to the breeding grounds) and survival.

(b) In building links in the opposite direction, we study behavioural and neuro-endocrine traits that appear to be relatively simply genetically integrated and that comprise many aspects of life history (behavioural syndromes, coping strategies or animal personalities).

2. Mechanisms
Early studies of life histories concentrated on measuring the fitness consequences of different trait values, enabling the trait value giving the highest fitness to be identified. However, the heritable neuro-endocrine and behavioural mechanisms that underlie life-history traits may also act as evolutionary constraints. When these are taken into account, the evolutionarily equilibrium trait value may differ from that giving highest fitness when a single trait is considered. The three general categories of mechanism that can affect the evolutionary equilibrium in this way and that are of interest to us are:

(a) genetic determination mechanisms (i.e. genetic co-variance)

(b) physiological mechanisms involving environmental and internal cues acting during development and at later stages affecting phenotypic traits and plasticity (i.e. mechanisms underlying gene – environment interactions)

3. Effects of life-history traits on population demography and dynamics, and feedback of these on life-history traits
Ecology spans a range of levels of biological organisation (individuals, populations, communities) which need to be integrated. Our ultimate aim is to understand the characteristics of entities at one level in terms of processes occurring at a lower level. Our goal is to understand the effects of evolutionarily equilibrium life histories on population demography and dynamics (fluctuations of population numbers around a mean). In respect to this, not only the mean, but also the variance, in life history traits may have an important effect. Moreover, population demography and dynamics can themselves act as important selection pressures on life history traits, for instance via density-dependent and frequency-dependent selection. Genetic and game theory models are needed to understand this feedback between individual and population levels of organisation. Thus, for a complete understanding of processes at both the individual and the population level, it is essential to study this two-way interaction between the life-history and population characteristics.