Cougars

The cougar (Puma concolor) may not be endangered in the Western United States however a localized population decline in Zion National Park has lead to some wide ranging impacts for species far down the Trophic cascade (Ripple 2003).  Increased tourism and human visitation in Zion has lead this once safe refuge for cougars into an area with scattered populations and local migrations from the area.  Cougar populations have shown significant displacement since the 1930's. A 2006 study documented areas that have been abandoned by cougars and compared them to areas currently inhabited by cougars and areas that have never had cougar populations.

Reduced cougar densities has subsequently lead to an increase in mule deer (Odocoileus hemionus) populations within the park (Ripple 2006).  These deers in turn have increased their consumption of the riparian cottonwood trees (Populus fremontii) as they are allowed increased browsing intensities.

 The decrease in riparian vegetation has resulted in large amounts of bank erosion along Zion's rivers and creeks.  Bank erosion has been show to have negative effects on riparian zones and decreases biodiversity among aquatic and terrestrial species (Ripple 2003) .  Impacts include decreases in shade which lead to an increase in average water temperatures .  Many aquatic species have a narrow tolerance for any temperature change even a fraction above or below their small optimal range.  This species characteristic can be seen in salmon populations in our region, the Pacific Northwest.  Riparian zones also provide a habitat and a protective cover for many species.  Together, the decreased riparian vegetation in Zion has resulted in the reduced abundance of amphibians, lizards and butterflies.  Riparian zones serve as the interface between terrestrial and aquatic ecosystems and allow for some of the most biologically diverse habitats on earth as wells as providing essential ecosystem functions (Gregory 1991).

Image source:  Phillip Colla, oceanlight.com