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State and trends


adjoining land uses do not compromise desired conservation objectives.


Rittenhouse and others (2012) found that changes in species richness and abundance for birds were mainly associated with changes in non-dominant types of land cover, for example grassland or shrubland habitats within an area dominated by forests, or forest patches within an extensive area of grasslands. But in many ecoregions, different types of land cover were associated with species richness than were associated with abundance. Conversion of natural to anthropogenic land cover was more strongly associated with changes in bird species richness and abundance than persistence of natural land cover in nearly all ecoregions. In addition, different co-variates were more strongly associated with species richness than with abundance in 11 of 17 ecoregions; that is, different parameters affected richness rather than abundance. Loss of grassland and shrubland patches affected bird species richness and abundance in forested ecoregions. Loss of wetlands was associated with bird abundance in forested ecoregions. These findings highlight the value of understanding changes in non-dominant land-cover types within a landscape and their association with bird diversity. These results were also consistent with similar findings by Pidgeon et al. (2007) regarding expansions of housing development and findings by Radeloff et al. (2010), who studied the expansion of developed areas in the wildland-urban interface.


Climate change


All the above and below trends take shape within the context of an increasingly pervasive driver: climate change, caused primarily by anthropogenic emissions of greenhouse gases.


Climate change alters habitat, temperature, and


phenology, and thus has a direct impact on biodiversity. Scientific evidence for climate-related species migrations emerged in the early 2000s (Walter et al. 2001). The biggest concern is that species are in effect losing habitat; this has been predicted for more than half of American bird species (National Audubon Society 2015; Langham et al. 2015; Schuetz et al. 2015) as migration patterns are being


disrupted, and simulations have predicted similar changes in forest composition as the tree lines move north (Scheller and Mladenoff 2005), although it will be more difficult for trees to migrate (Iverson and Schwartz 2004). Chen et al. (2011) provide a general model on range shifts of species at least partially induced by climate change.Stewart et al .(2015) created a model to assess the potential risk posed to pikas (Ochotonidae) and other climate-sensitive mammals by climate change. Their model matched previous findings and predicted high levels of extirpation of pikas in study sites across California, with the size of areas of rocky debris and summer temperatures being the best predictors of range.


Wildfires exacerbated by prolonged drought on the West Coast have also driven species into new geographic territories; coastal flooding will have a similar effect. Concerns have also been raised about the tropicalization of marine ecosystems, increasing the range of invasive species such as lionfish, in addition to the threats posed by ocean acidification and warming on coral, which cannot migrate and suffer from related ocean acidification and temperature shift events.


Problem areas related to these emerging concerns include changes in the population ranges and dynamics of invasive alien species. This is perhaps the most noteworthy concern, as has been seen with the spread of the mountain pine beetle on the west coast and the alien invasive zebra mussel (Dreissena polymorpha) in the Great Lakes region. Higher temperatures and shorter winters lengthen the breeding window of such species and allow them to spread to different regions, where they have fewer or no natural predators. Medical practitioners and veterinarians will also have to be aware of the climate-assisted migration of species posing dangers to humans and livestock. Wildlife diseases caused by non-native pathogens, such as West Nile virus, have killed thousands of birds and potentially threaten many different wildlife species. The link between domesticated and wild animals is important as well: for example, respiratory diseases found in domestic sheep have been linked to population declines of the threatened bighorn sheep (Ovis Canadensis) (Wehausen et al. 2011).


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