In this post, Jonathan Rhodes discusses a paper he recently handled by Chrystel Losier and colleagues “Adjustments in habitat selection to changing availability induce fitness costs for a threatened ungulate”
Habitat selection is an important determinant of the distribution of individuals, but can also have important implications for the fitness of individuals (DeCesare et al. 2014). Although, methods for the empirical analysis of habitat selection and movement have come a long way (Moorcroft 2012) we still know little about the fitness consequences of habitat selection. Over the past decade there has been considerable interest in the idea of attractive sinks/ecological traps where habitat selection is maladaptive and results in a decline in fitness (Delibes et al. 2001). The idea here is that individuals respond to cues that are negatively correlated with fitness and actively select habitats where their fitness is lower than other habitats. Over this period there has also been an increasing interest in functional responses in habitat selection. Functional responses are where preferences for habitat types change with the proportions of each habitat type available (Matthiopoulos et al. 2011). Yet, we still know little about the fitness implications of functional responses as a habitat selection strategy.
In their new paper, Losier et al. start to address precisely this issue using caribou in the boreal forests of Québec as a case study species. Using telemetry data for 83 caribou and resource selection functions, they first characterised habitat selection and functional responses. They found that caribou preferred open conifer forests with open areas and lichen to other habitat types. But they also found two functional responses: (1) caribou preferences for mixed/deciduous stands declined as the proportion of their home ranges that were 6- to 20-year old clear cuts increased; and (2) preferences for areas close to 6- to 20-year old clear cuts increased as the proportion of their home ranges that were 6- to 20-year old clear cuts increased. Importantly, the second functional response differed between individuals that died and those that survived; individuals that died were the ones that increased their preference for areas close to 6- to 20-year old clear cuts with increasing proportions of 6- to 20-year old clear cuts the most. The relationship between survival and the functional response indicates a measurable impact on fitness attributable to a functional response. The mechanism for the higher mortality may be related to 6- to 20-year old clear cuts attracting moose and wolves, making these habitats more risky. But the driver of the seemingly maladaptive behaviour that results in an increase in mortality is, as yet, unknown.
This is one of the first studies to quantify the fitness implications of a functional response, but why does this matter for management? Losier et al. suggest that one implication is that it implies a need to reduce the “riskiness” of the 6- to 20-year old clear cuts. This could be achieved by removing deciduous vegetation and that would make these habitats less attractive to moose and therefore also wolves. The literature on attractive sinks and ecological traps identifies strategies that aim to remove cues that drive maladaptive habitat selection (Battin 2004) and these types of strategies may also be applicable here. The impact of functional responses for fitness described by Losier et al. represents a more subtle form of maladaptive selection than attractive sinks and ecological traps. However, this work opens up an exciting avenue for better linking fitness and population dynamics with habitat selection that can inform management.
Battin J. (2004) When good animals love bad habitats: ecological traps and the conservation of animal populations. Conserv Biol 18, 1482-1491.
DeCesare N.J., Hebblewhite M., Bradley M., Hervieux D., Neufeld L., Musiani M. (2014) Linking habitat selection and predation risk to spatial variation in survival. J Anim Ecol 83, 343-352.
Delibes M., Ferreras P., Gaona P. (2001) Attractive sinks, or how individual behavioural decisions determine source-sink dynamics. Ecol Lett 4, 401-403.
Matthiopoulos J., Hebblewhite M., Aarts G., Fieberg J. (2011) Generalized functional responses for species distributions. Ecology 92, 583-589.
Moorcroft P.R. (2012) Mechanistic approaches to understanding and predicting mammalian space use: recent advances, future directions. J Mammal 93, 903-916.