Discussion | gisproject

Connectivity

There is a strong scientific foundation for the importance of maintaining habitat area and connectivity. As such, conservationists must evaluate which patches that are most significant to this network connectivity of habitat patches. Optimal application of graph theory to species assessment and criteria development requires understanding how changes in structural connectivity affect functional connectivity. Links between structural and functional connectivity depend on complex interactions between landscape pattern and dispersal abilities of particular species (Saura et al., 2011). Such analyses can be used to justify minimizing changes at key high-risk distances or to recommend conducting research to better accommodate these connectivity losses. Future research is needed in how much or where stepping stones should be placed to improve connectivity of the small patch networks. Habitat quality could also be improved in those small connected networks to increase water availability and vegetation cover.

In summary, the approach I used here is useful for evaluating the consequences of environmental changes or management actions that alter landscape pattern (e.g., habitat loss, conservation, or restoration). Alterations to habitat area and connectivity will likely display changes in ecological processes in landscapes. Maintaining amounts of habitat or populations is a core conservation goal for calculating conservation value of individual patches based on their function in a landscape (Bodin and Saura, 2010).

MaxEnt

By year 2070, MaxEnt suggest that the climates currently inhabited by D. plexippus should disappear from within the current protected area boundaries (Figure 10). Monarch are unique in that they have a strong interspecific dependence on the oyamel fir trees they overwinter on, and so it is critical to project their distributions under the same climate change scenarios in order to understand how climate change will alter monarch distributions. The models show that there is asynchrony from these species and that the fir trees do not shift their range with the monarch population as time passes. This result suggests a threat to the overwintering colonies of the monarch’s, as suitable habitat would disappear. However, even if monarch populations could survive elsewhere, it is not known whether the monarch butterfly would ‘‘accept’’ a transfer of their overwinter areas to different mountains with different fir species. Therefore, in light of these results, management options are needed to plan for future butterfly habitat. One such management strategy has been suggested by Sáenz-Romero et al., (2012). The authors propose that assisted migration of A. religiosa is needed. The tree populations would require an upward shift of about 275–300 m for populations to inhabit the same climate in 2030 that they inhabit today. This study was only looking at the Monarch Biosphere Reserve and my more global results show an even drastic change that would need more drastic migration of trees. This assisted migration idea would only benefit monarchs under two conditions: (a) the newly colonized habitat was also suitable to monarchs, and (b) the addition of the trees at the new habitat would provide roosting substrate that was not otherwise available. Due to the fact that monarch distribution and oyamel fir tree distribution does not follow each other throughout time, this suggests that suitable microclimate will change in the future for both species.

Monarchs present an interesting case, as they migrate every year to recolonize overwintering areas, and might thus be better able to encounter areas of suitable habitat than species with restricted dispersal capabilities. The importance of dispersal was highlighted by a recent survey of climate change effects on birds, mammals, and butterflies in Mexico, in which methods identical to those used here were applied to 1,870 species (Peterson et al., 2002): dispersal was crucial in shaping what outcome is expected for each species. Under the assumption of universal dispersal ability, species on average neither increased nor decreased in prospective distributional area; under assumptions of no dispersal, however, all species declined.

It is important to bear in mind that ecological niche models attempt to model the geographic distribution of areas appropriate for the species in ecological terms. For many ecological and historical reasons, species almost never inhabit the entire spatial distribution of their ecological niches (Peterson et al., 1999). It is possible that monarchs do not occupy all habitable areas even within their known overwintering colonies. It could be that the benefits of dense aggregations of into many small local populations means that only a subset of potential habitat will be used, although the frequent discovery of new colonies (Garcıa-Serrano et al., 2004) suggests that more monarch overwintering areas remain to be discovered. Effective long-term conservation will depend on effective detection and monitoring of monarch overwintering areas.