Modeling Habitat Connectivity for the Monarch Butterfly among Protected Areas and its Significance in Conservation

This study analyzes (1) the connectivity of Monarch Butterfly (Danaus plexippus) habitat in Mexico (2) how climate change will affect the future distribution of this species, and their oyamel fir tree habitat (Abies religiosa).

 

Habitat Connectivity

 

Funding for conservation is always scarce, thus managers must decide which habitat sites are the main concern for protection. Although habitat patch size is an important factor in determining species abundance, as the theory of island biogeography (MacArthur and Wilson 1967) states, other factors such as habitat connectivity must be considered in conservation planning efforts. Conservation planning has assumed that species are static entities and do not partake in long distance dispersal (Pressey et al., 2007). However, many of the world’s vertebrate species, and even more insect species make either nomadic or migratory long-distance dispersal movements (Robinson et al., 2009).

 

Habitat connectivity is an important aspect when designing protected areas because different habitat patches possess different roles within the landscape network. Different patches may serve as better sites for shelter, foraging or breeding for species (Saura and Rubio, 2010). Depending on patches’ topological position in the network even small patches can provide benefits, acting as stepping stones to facilitate dispersal to larger patches. The connectivity of habitat patches increases the effective size of existing protected areas and ultimately aids in species persistence. It has also long been known that loss of connectivity within a patch network can lead to localized extinction events (Carroll et al., 2004). Habitat connectivity studies are beneficial in mapping dispersal routes of populations in more specific ways and help to better identify areas of importance.

 

Climate Change

 

Studies on habitat connectivity mostly tackle current issues related to habitat fragmentation and habitat loss. Future consequences that may result from climate change have not been studied extensively. The area occupied by a species is, to a large extent, determined by the climatic conditions—with temperature change playing a key part (Berestycki et al., 2009). These alterations in climate could affect habitat quality and network links between habitat patches. The combined effects of changes in land use, habitat loss, and climate change are all expected to affect the persistence of species by changing the distribution and connectivity of resources and habitat (O'Farrill et al., 2014) and therefore should all be considered. This study combines all these factors to give insight into both present and future problems that these species will come in contact with.

 

Climate change manifests itself through changes in temperature and extreme precipitation pattern intensities (Kundzewicz et al., 2007). The three lowest overwintering population sizes of monarch density on record have been recorded in the last ten years (Brower et al., 2012). This includes the all-time low of 0.67 hectares (measure of monarch density on oyamel fir trees) recorded last winter. Three times (2002, 2004, and 2010) in the last decade massive Pacific weather systems have moved into central Mexico in January and February. Each of these events resulted in heavy rain, often accompanied by hail, high winds, or freezing temperatures that devastated the monarch overwintering populations (Brower et al., 2004). Climate change will alter suitable climatic niches, resulting in shifts in species distributions (Trakhtenbrot et al., 2005). The geographical location of protected sites may not be useful in their duty to provide species a suitable habitat for continued survival.