Importance of migratory habitats
Submitted by editor on 7 September 2017.
Get the paper! Northern pintail males and females.
By Ruscena Wiederholt and Brady Mattsson
Conserving or managing migratory species is notoriously challenging since their seasonal movements can cross international borders and continents – even spanning thousands of kilometers. Migratory species use these habitats for breeding, overwintering, or stopover sites to refuel during migration. The importance of these areas for population viability is often poorly understood. Consequently, management efforts may not be focused on the most crucial areas for a species. To tackle this problem, we developed a modeling framework to quantify the importance of habitat areas and pathways used by migratory species.
Monarch butterflies in their overwintering habitat in central Mexico.
Our framework is based on an approach that was originally developed for metapopulations, and it estimates the per capita contributions of habitats and migratory pathways. These contributions measure the number of individuals (in the entire population) that were generated from the average individual that used a particular habitat or pathway during the previous year. For example, a contribution of 2 for a habitat means that an average individual using that habitat survives and has one surviving offspring, or doesn’t survive and has two surviving offspring. A contribution above one indicates a source habitat or pathway that is contributing individuals to the population. By contrast, a contribution less than one represents a sink habitat or pathway that results in a net loss of individuals in the population.
To test our model, we ran a series of perturbation experiments with a simple 2 by 2 migratory network and found some interesting results. First, the contribution of a habitat depends not only on local demographics but also on demographic processes in other habitats and pathways. For example, the contribution of a habitat can be improved if it receives more migrants from a higher quality habitat (one with higher vital rates). Conversely, lowering a habitat’s or pathway’s quality can reverberate throughout the system and decrease the contributions of other habitats and pathways. Finally, we found that in a habitat, if part of the population is non-migratory but still has moderate survival rates, this can help buffer against lowered survival rates in other habitats. This may be a mechanism driving the evolution of partial versus complete migration.
This framework was designed to be flexible; it can be used to examine the ranking of habitats used by migratory species with any migratory strategy (e.g. complete migration versus partial migration), and it can be applied to complex migratory networks with many habitats. We provide R code for the model. It can be used for studies of ecology and evolution, and it can help managers and decision-makers prioritize areas for conservation and management efforts.
References
Mattsson, B. J., Runge, M. C., Devries, J. H., Boomer, G. S., Eadie, J. M., Haukos, D. A., Fleskes, J. P., Koons, D. N., Thogmartin, W. E. and Clark, R. G. 2012. A modeling framework for integrated harvest and habitat management of North American waterfowl: Case-study of northern pintail metapopulation dynamics. – Ecol. Modell. 225: 146–158.
Oberhauser, K., Wiederholt, R., Diffendorfer, J. E., Semmens, D., Ries, L., Thogmartin, W. E., Lopez-Hoffman, L. and Semmens, B. 2017. A trans‐national monarch butterfly population model and implications for regional conservation priorities. – Ecol. Entomol. 42: 51–60.
Runge, J. P. et al. 2006. The role of local populations within a landscape context: defining and classifying sources and sinks. – Am. Nat. 167: 925–938.