A general models for phenotypic evolution in fluctuating environments in populations subject to density regulation will be parameterized and validated through an access to one of the largest individual-based long-term field studies of any vertebrate species including data on more than 36000 individual house sparrows from 18 populations on islands within a large geographical area in northern Norway. This enables quantification of the influence of processes rarely analysed before under natural conditions. A central focus will be to derive new metrics that describe how the degree of persistence of a population to environmental change depends upon its size and population dynamic characteristics.
According to Fisher’s Fundamental Theorem of Natural Selection the rate of evolutionary response to selection should be exactly equal to the additive genetic variance in the character. However, one of the key challenges in evolutionary biology is that in natural populations the recorded responses to phenotypic selection in heritable characters are much less than expected or even completely lacking. In EcoEvoRescue we have shown that this paradox is due to ignoring in the analyses important deteriorating effects, which were introduced by Fisher himself, such as fluctuations in the environments, genetic drift and mutations. An important implication of this general insight is that the capacity of species to adapt to altered environments by evolving new adaptations as a response to selection is far less than expected.
Our model system has been used to quantify how three major ecological drivers (fluctuations in population size, spatio-temporal covariation in key environmental variables and dispersal) affect the persistence of natural populations. It is now empirically shown for the first time that there exists a lower threshold of population size at which demographic stochasticity causes sever decrease in the population growth rate and strongly reduces the capability to evolve adaptive changes as response to alterations of the environment. This means that there exist some critical lower population sizes at which the future persistence of populations will be dramatically reduced. The models and statistical methods developed in this project provide a general approach for how to calculate these threshold population sizes which must be exceeded to ensure population viability.
