Habitat-performance relationships of a large mammal on a predator-free island dominated by humans

Abstract

The demographic consequences of changes in habitat use driven by human modification of landscape, and/or changes in climate, are important for any species. We investigated habitat-performance relationships in a declining island population of a large mammal, the moose (Alces alces), in an environment that is predator-free but dominated by humans. We used a combination of demographic data, knowledge of habitat selection, and multiannual movement data of female moose (n = 17) to understand how space use patterns affect fecundity and calf survival. The calving rate was 0.64 and was similar to calving rates reported in other populations. Calf survival was 0.22 (annually) and 0.32 (postsummer), which are particularly low compared to other populations where postsummer survival is typically above 0.7. Home ranges were mainly composed of arable land (>40%), and selection for arable land was higher in winter than in summer, which contrasts with previous studies. Females that spent more time in broadleaf forest in the summer prior to the rut had higher fecundity rates, while more time spent in arable land resulted in lower fecundity rates. Females that spent more time in thicket/scrubland habitats during winter had lower calf survival, while females that had higher use of mixed forests tended to have higher calf survival. The dominance, and subsequent use, of suboptimal foraging habitats may lead to poor body condition of females at parturition, which may lower calf body weights and affect the mother's ability to lactate. In addition, our results indicated that the growing season has advanced significantly in recent decades, which may be causing a mismatch between parturition and optimal resource availability. These effects may exacerbate the female's ability to meet the energetic demands of lactation. Therefore, the observed low calf survival appears to be caused by a combination of factors related to current land use and may also be due to changing vegetation phenology. These results have important implications for the management of species in human-dominated landscapes in the face of climate change, and for an increased understanding of how species may adapt to future land use and climate change.

Keywords: fitness; habitat selection; parturition; performance; population dynamics; reproduction; Öland.

Figure 1

The study species, moose (Alces alces), wearing a GPS collar in a typical thicket‐type habitat on Öland. Photo: Fredrik Stenbacka

Figure 2

The location of the study area, Öland, including the coarse habitat structure of the island. In the right panel, yellow areas are arable land, green areas are forested, and the light pink area is the sparsely vegetated Stora Alvaret. The dashed line indicates the divide between the north and south, and the black dots are the average location for the females in the south (n = 7) and the north (n = 10)

Figure 3

Kaplan–Meier estimates of moose calf survival: (a) survival estimates for the north and the south of Öland; (b) survival estimates during the 3 years of the study, 2012, 2013, and 2014; and (c) survival estimates of calves that are either singletons or twins. The lines indicate the Kaplan–Meier estimate at each time step, and the shaded areas are the 95% confidence intervals. Time step 0 is the birth of the calf, 1 is the start of summer, 2 is after summer but before the hunt, and 3 is late winter

Figure 4

Modeled relationships and uncertainty of the top three models containing the response (calf survival) and explanatory variables of (a) Mires (MIs) + Mixed Forest (MXw) and Twin; (b) Age + MXw + Thickets (THw); and (c) MIs + THw + Twin. “w” and “s” indicate the proportion of time spent in a habitat during winter (w) or summer (s)

Figure 5

Results of hierarchical partitioning to measure the importance of explanatory variables included in Table 3. The percentage indicates the total contribution of a variable toward explained variation. AL, arable land; CL, clear‐felled area; MI, mire; MX, mixed forest; SV, sparsely vegetated area; THw, thickets; YF, young forest; w, winter; and s, summer. + and − indicate the direction of the relationship