Biology subjects

Van Dooren, T. J.

Publications and source records attributed to Van Dooren, T. J..

6 recordsLinked to original sources

bioRxiv2024

Effects of environmental and individual variation on time patterns of extinction in small experimental populations.

Predicting the fate of small populations is essential in ecology, epidemiology and conservation biology. Small populations can go extinct quickly or can develop into large established populations. These can still go extinct through demographic stochasticity, especially when declines in mean population size or large size fluctuations drive them into an extinction vortex. Individual life stage and environmental conditions experienced by founding individuals are two factors expected to determine the fate of small populations. When they dont go extinct, life stage effects are expected to wash out. Initial environmental differences equally so, unless differences in environmental conditions continue to occur. We used the parthenogenetic Collembola Folsomia candida to investigate such effects in a crossed treatment on 290 replicate populations, each initiated with a single individual. Populations were initiated with founders of three different life stages and subjected to four levels of culling. Their extinction times were recorded in a period of up to 41 weeks after initiation. We fitted the parameters of an age-structured multi-type branching process model to extinction rates observed in the first weeks after initiation. As predicted by the model, extinction probabilities early in the experiment increased with the level of culling. Extinction probabilities were larger in populations founded by non-reproducing individuals. These decreased over time, presumably because of the onset of reproduction. In established populations, extinction probabilities increased with culling level and the effects of the founder stage disappeared, except for a late increase in extinction probability in populations founded by newborns. This increase was not expected and forced us to reconsider when transient effects of the initial state would end. We hypothesize that it is due to effects of size-structured competition in this system. The results show that predictors of extinction probability can be shared between small and established populations. Transient dynamics of extinction risk can be long, with phases even mimicking a stationarity followed by the onset of an extinction vortex.

evolutionary biology↗

bioRxiv2024

Extinction probabilities of small structured populations: adequate short-term model predictions in Folsomia candida

Population management requires predictions of extinction risk based on a general understanding of these risks and on system-specific modelling. Life tables, available for numerous populations and species, permit calculating population growth and the construction of multi-type branching process models which predict population survivorship and ultimate extinction probabilities. We exemplify this approach and tailor it to an experimental model to predict extinction probabilities per unit of time. In age-structured populations, founders from different age classes lead to different predicted extinction probabilities. Age effects interact with environmental effects such as culling levels, which influence population growth rates. We assess the accuracy of predictions based on an age-structured matrix model, in an extinction experiment over an eight-week period on the springtail Folsomia candida, with crossed founder age and culling level treatments. Using parameter estimates from an accessory experiment, the fit of model predictions to observed extinction probabilities was generally good. A modified branching process model which allowed culling events between and at observations reduced prediction error. However, additionally maximizing the likelihood of observed extinction probabilities based on survival and fecundity parameters, or on a parameter which concentrated fecundity within a subinterval, did not significantly reduce prediction error according to the AICc. Our study shows that satisfactory predictions of establishment probabilities and of the initial persistence of small populations can be made using multi-type branching processes and available parameter estimates. Predictions can be improved by integrating knowledge of when events occur within intervals. This can be done without additional parameter estimation.

ecology↗

bioRxiv2023

A model-based assessment of adaptation in embryonic life histories of annual killifish

Adaptation requires an evolving strategy and an environment. Given an environment, we predict or estimate which strategies are adapted. Given a strategy, we want to know in which environments it might be adapted. Example calculations aiming to determine such environments, named evolutionarily singular environments ESE, are presented using lab data on embryonic life histories of Austrolebias annual killifish. Annual killifish embryos can arrest development and survive desiccation of temporary ponds in the soil. They might implement diversified bet-hedging, generally seen as an adaptation to uncertain environments. Using parameter estimates and parsimonious assumptions, a population dynamical model is constructed with explicit developmental stages. Using invasion fitness gradients of rates of development and hatching probabilities, it is investigated whether these could be adapted to pond filling regimes with gradual filling and drying and deterministic within-year variation only. The life history as a whole is not adapted to the regular within-year annual cycles investigated, with one or two periods where reproduction can occur. Faster development rates were always favoured, just as in constant environments. Only for hatching probabilities, pond filling regimes were found which made their invasion fitness sensitivities zero. However, the observed trait values did not have long-term evolutionary stability in these ESE. Therefore, neither the developmental rates nor the hatching strategy seem adapted to within-year patterns of environmental change.

evolutionary biology↗

bioRxiv2020

Egg size does not universally predict embryonic resources and hatchling size across annual killifish species

Egg size has a crucial impact on the reproductive success of a mother and the performance of her offspring. It is therefore reasonable to employ egg size as a proxy for egg content when studying variation in offspring performance. Here, we tested species differences in allometries of several egg content parameters with egg area. We measured individual eggs in five species of annual killifish (Cyprinodontiformes), a group of fish where egg banks permit population survival over dry season. Apart from comparing allometric scaling exponents, amounts and compositions of egg components across the different species, we assessed the explanatory power of egg area for egg wet and dry weight and for hatchling size. We found notable species-specific allometries between egg area and the other egg parameters (egg dry weight and water content, elemental composition and triglyceride content). Across species, egg area predicted egg wet weight with highest power. Within species, coefficients of determination were largest in Austrolebias elongatus, a large piscivorous species with large eggs. Our study shows that systematically using egg area as a proxy of egg content between different species can ignore relevant species-specific differences and mask within-species variability in egg content.

zoology↗

bioRxiv2019

Determinants of growth and body size in Austrolebias South-American annual killifish

Patterns of size variation in fish are supposed to be generated by growth differences, not by egg or hatchling size variation. However, annual killifish live in temporary ponds with a limited time period available for growth and reproduction. It has therefore been hypothesized that among annual killifish, hatchling size variation should be of large relative importance to generate adaptive adult size variation. Using growth curves of 203 individuals from 18 Austrolebias species raised in a common environment, we demonstrate that hatchling size variation indeed is a main determinant of adult size variation in annual killifish, in agreement with the time constraint hypothesis. Furthermore, we find an increased early growth rate in piscivorous species augmenting their difference in size from small congeneric species. This should be adaptive if size differences determine predation success. Environmental effects of spatial location of the population of origin on hatchling size and growth suggest that the time constraint might be weakened in populations occurring near the Atlantic coast. Our study reveals how extreme environments demand specific life history solutions to achieve adaptive size variation and that there might be scope for local adaptations in growth trajectories.

evolutionary biology↗

bioRxiv2019

Adaptational lags during periods of environmental change

Effects of climate change can be handled by means of mitigation and adaptation. In the biological sciences, adaptations are solutions which evolved when organisms needed to match an ecological challenge. Based on Adaptive Dynamics theory, a definition is proposed of adapted states and adaptational lags applicable during periods with environmental change of any speed. Adaptation can thus be studied when it emerges from complex eco-evolutionary processes or when targets for adaptation are not defined a priori. The approach is exemplified with a model for delayed germination in an annual plant. Plasticity and maternal effects are often presumed to be adaptive and added to the model to investigate lags in these modes of trait determination. Adaptational lags can change sign and to understand their dynamics, effects of trait space boundaries and characteristics of years with large numbers of recruits had to be considered. Adaptational lags can be crucial elements of adaptive control strategies for managed ecosystems. To demonstrate their practical relevance, examples from pest management show that evolutionary adaptation has been used to infer targets of control. Adaptational lags then serve as measures of the distance to the control target and become integral elements of strategies for adaptive pest population management.

evolutionary biology↗