Accounting for Fitness: Combining Survival and Selection when Assessing Wildlife-Habitat Relationships

Abstract

Assessing the viability of a population requires understanding of the resources used by animals to determine how those resources affect long-term population persistence. To understand the true importance of resources, one must consider both selection (where a species occurs) and fitness (reproduction and survival) associated with the use of those resources. Failure to do so may result in incorrect assessments of habitat quality and inappropriate management activities. We illustrate the importance of considering both occurrence and fitness metrics when assessing habitat requirements for the endangered greater sage-grouse in Alberta, Canada. This population is experiencing low recruitment, so we assess resource use during the brood-rearing period to identify management priorities. First, we develop logistic regression occurrence models fitted with habitat covariates. Second, we use proportional hazard survival analysis to assess chick survival (fitness component) associated with habitat and climatic covariates. Sage-grouse show strong selection for sagebrush cover at both patch (smaller) and area (larger) spatial scales, and weak selection for forbs at the patch scale only. Drought conditions based on an index combining growing degree days and spring precipitation strongly reduced chick survival. While hens selected for taller grass and more sagebrush cover, only taller grass cover also enhanced chick survival. We show that sage-grouse may not recognize all ecological cues that enhance chick survival. Management activities targeted at providing habitats that sage-grouse are likely to use in addition to those that enhance survival are most likely to ensure the long-term viability of this population. Our techniques account for both occurrence and fitness in habitat quality assessments and, in general, the approach should be applicable to other species or ecosystems.

Habitat–performance relationships: finding the right metric at a given spatial scale

“…For instance, the results of Dussault et al (2005) were in agreement with the 'avoidance of limiting factors at broader scale' hypothesis when finding, using GPS telemetry, that moose (Alces alces) indirectly selected against wolves by avoiding areas with the lowest snowfall at the landscape scale and selected for areas with abundant food at the home-range scale. In contrast, Aldridge & Boyce (2008) did not find any difference between spatial scales in habitat selection by sage grouse; at both patch and area scales, birds selected for sagebrush cover. There are several processes that could account for deviations from the 'avoidance of limiting factors at broader scale' hypothesis.…”

Establishing the link between habitat selection and animal population dynamics

“…Instead, we should simply select a sufficiently expandable inferential framework, verify its robustness (Barry and Elith 2006), and begin fleshing it out with biological mechanisms (Austin 2002, Railsback et al 2003, Guisan and Thuiller 2005, Moorcroft and Lewis 2006, McLoughlin et al 2010. Here, we have contributed to this increasingly active area of research (Tyre et al 2001, Railsback et al 2003, Aldridge and Boyce 2008, Gaillard et al 2010, Hoffman et al 2010, DeCesare et al 2014.…”

“…While sharing with other recent work (Mieszkowska et al 2013) the motivation of confronting spatiotemporal dynamics with data empirically, our model's mechanistic component is greater and more expandable. Further, rather than requiring geo-referenced data on growth (in the form of spatial layers for survival and fecundity, e.g., Aldridge and Boyce [2008], DeCesare et al [2014]), we fit to nonspatial population time series, such as those available from long-term monitoring studies (e.g., Saether 1997, Gaillard et al 1998, Brook et al 2000, Parmesan and Yohe 2003, Stuart et al 2004, Strayer et al 2006.…”

Relating resource use to body condition and survival of Ozark hellbenders Cryptobranchus alleganiensis bishopi

“…Variation in the use of coarse substrate and distance to cover suggest the potential for variation in biological outcomes (Aldridge & Boyce 2008). However, our model selection results indicate that variation in biological outcomes was not explained by variation in use of substrate features over a relatively short time period (i.e.…”

“…Threatened and endangered species are often faced with greater difficulties in gaining resources necessary for survival and reproduction than common species (Thomas 1990), yet it is not always known how resource use affects animals at population and individual levels. Investigations into how individual resource use affects individual biological outcomes should be conducted to gain reliable knowledge of ways of improving population sustainability (Aldridge & Boyce 2008). These investigations are generally lacking in the literature because of difficulty in collecting resource use and biological outcome data or because it is assumed that selection for resources leads to beneficial outcomes (Thomas & Taylor 2006).…”