Discussion
The outcomes from this project indicate that spatial, environmental and climate factors all play a significant role in habitat occupancy by collared pikas.
a. Spatial and Environmental Factors
The outputs from this project affirm that the spatial configuration of patches and the connectivity between them, are key factors influencing the number of pikas on a talus patch in any one year and the number of years that a patch is occupied. This outcome is expected since larger patches will naturally provide greater opportunities for nesting while greater connectivity provides opportunities for dispersal, particularly for juvenile pikas seeking to establish a territory. This result is consistent with well-established metapopulation theory which links population size to patch size and the probability of patch extirpation and re-colonization with connectivity (Hanski 2002; Moilenan et al. 1998).
Another important factor influencing numbers of pika and habitat occupancy is the vegetation cover adjacent to the patch, with a positive relationship between the number of pikas and length of patch occupation and percent cover of Dryas octopetala and a negative relationship between the years of occupation and percent cover of graminoid species (alpine grasses). Dryas octopetala is a preferred forage species, particularly when flowering (Figure 20) (Morrison et al. 2004). The finding for graminoids is unusual, since graminoids have been shown to represent a high proportion of the content of haypiles (Hudson et al 2008). One reason for this result may be that graminoids tend may dominate herb species, so areas with a high percent graminoid composition will lack the diversity of plant species observed to be used by pikas (Hudson et al 2008). Access to high quality forage is essential to pika survival, as individuals must gather enough plant material over the few summer months of their active season to have enough food and nest material to last through the long and variable winter season.
One factor that, unexpectedly, did not appear to be significant is aspect. The reason for this lack of relationship may be that the data used was taken only from the east- and west-facing slopes of the study area. A future analysis will incorporate data from the south-facing slope, where pika populations are larger and appear to be less prone to local extirpations.
Another important factor influencing numbers of pika and habitat occupancy is the vegetation cover adjacent to the patch, with a positive relationship between the number of pikas and length of patch occupation and percent cover of Dryas octopetala and a negative relationship between the years of occupation and percent cover of graminoid species (alpine grasses). Dryas octopetala is a preferred forage species, particularly when flowering (Figure 20) (Morrison et al. 2004). The finding for graminoids is unusual, since graminoids have been shown to represent a high proportion of the content of haypiles (Hudson et al 2008). One reason for this result may be that graminoids tend may dominate herb species, so areas with a high percent graminoid composition will lack the diversity of plant species observed to be used by pikas (Hudson et al 2008). Access to high quality forage is essential to pika survival, as individuals must gather enough plant material over the few summer months of their active season to have enough food and nest material to last through the long and variable winter season.
One factor that, unexpectedly, did not appear to be significant is aspect. The reason for this lack of relationship may be that the data used was taken only from the east- and west-facing slopes of the study area. A future analysis will incorporate data from the south-facing slope, where pika populations are larger and appear to be less prone to local extirpations.
Figure 20. Preferred forage of collared pikas at the study site (Hudson et al 2008)
The finding of talus topography (whether or not talus is level) being important to haypile occupancy may have something to do with the quality of the talus patch as habitat. Concave patches are more likely to accumulate snow and hold it past first snow melt. In addition, concave patches may be shadier or have poorer rain run-off.
b. Regional climate factors
This analysis indicates that climate has strong influence on pika populations. The results suggest that, despite the variability of winter climates within their habitat range, collared pikas are vulnerable to changes in temperature and the amount of snowfall. It is thought that snowfall plays an important role in pika over-winter survival by providing an insulating layer over the haypiles (Morrison and Hik 2007). Years where there is a low amount of winter precipitation may decrease the insulation of pika habitat and expose the animals to potentially lethal weather, such as freezing rain events.
Longer growing seasons are shown here to be positively correlated with pika numbers and patch occupancy. Pikas are likely to benefit from a longer growing season as it provides them with more opportunity for harvesting of vegetation for their haypiles and allows juveniles more time to gain body condition and establish a territory and haypile of their own(Morrison et al. 2009; Morrison and Hik 2007).
Longer growing seasons are shown here to be positively correlated with pika numbers and patch occupancy. Pikas are likely to benefit from a longer growing season as it provides them with more opportunity for harvesting of vegetation for their haypiles and allows juveniles more time to gain body condition and establish a territory and haypile of their own(Morrison et al. 2009; Morrison and Hik 2007).
Conclusion
Dryas octopetala flowers
The outcomes of this project do not tell us anything new about collared pikas, but they are consistent with what is known about the biology of the species. These analyses demonstrate that multivariate analysis can be a useful and appropriate tool for assessing the relationship between habitat and species dynamics at the habitat scales of the collared pika. The results also support the speculation that collared pikas are vulnerable to climate change and suggest that both climate and habitat factors need to be considered in evaluating the implication of future environmental changes on this species.
