Habitat Issues

 Habitat degradation from from the view of the Oregon Spotted Frog

Figure 1 - created by Heidi Rockney showing the effects of habitat degradation on birth rates and death rates of the Oregon Spotted frog compiled from data collected from scientific literature on the Oregon Spotted frog (references at bottom of page)



Oregon Spotted frogs are an endangered amphibian found only in the Pacific Northwest of the continental United States. They have suffered severe habitat disruptions that has led to a decrease in reproductive success and increased death rate. Specific ways that habitat damage has led to this are highlighted in figure 1 and explained in more detail below. 

The original range of the Oregon Spotted frog has been inferred from sightings, historical documentation and DNA analysis of museum specimens. They are only found in the Pacific Northwest throughout the Puget Sound valley, the south-central Cascades in Washington state, Willamette valley in Oregon state and in the lower Fraser river in Canada and possibly in northern areas in the Pit river in California, although they are now extinct in California. In 2001, a complete analysis of research and surveys to date was compiled. It was estimated that the Oregon Spotted frog was gone from 70-90% of its original territory.

Draining of a wetland. Photo credit: www.spencerspond.ca

Oregon Spotted frogs are highly associated with water and are rarely found out of or far from water. Due to their reliance on water, many of their life history traits revolve around the health and stability of the wetlands they inhabit. Oregon Spotted frogs are fond of shallow, warm wetlands including marshes, ponds, and seasonally flooded plains and prairies with slow moving, quiet water. They favor moderate vegetation that allows for some cover from predators, but also permits enough water exposure for free floating eggs to be exposed to adequate amounts of UV. They lay eggs communally in warm water shallows, usually in temporary ponds (ponds created during rainy seasons). Eggs and tadpoles have low survival rates due to desiccation and predation and alterations in water chemistry. Eggs typically hatch and tadpoles complete metamorphosis within one season and once they have reached adulthood, they keep to a very small home range and do not disperse farther than the water in their particular habitat allows. 

Oregon Spotted Frog juvenile. Photo credit: Heidi Rockney

Oregon Spotted frogs migrate short distances from breeding sites to overwintering sites.They prefer deeper waters such as spring systems for overwintering that typically do not freeze. Overwintering sites need to be connected to breeding sites via water; this requires a decent amount of wetland and water surface area with interconnecting channels.

Figure 2 - by Heidi Rockney illustrating the effects of habitat fragmentation compiled from research into problems with small populations from conservation biology textbook referenced at bottom of page,

Chief Joseph dam. Photo credit: Columbia basin research

Due to their necessary connection to water, Oregon Spotted frogs have suffered severe losses from habitat destruction and degradation from a variety of forms. Habitat alterations from direct destruction include dam construction, development and farming. In the development of the Puget Sound in Washington State, many wetlands have been completely destroyed by development. This has permanently eradicated many populations of the Oregon Spotted frog from the Puget Sound area. Humans have made several alterations to wetland areas by constructing dams that have completely fragmented existing populations (see figure 2 for specific affects of fragmentation). Water levels and water channels connecting water sources have been altered and create ineffective breeding sites and cut off passageways for migration between breeding sites and overwintering sites. Farmland introduces runoff pollutants into water systems and habitat damage from grazing livestock have changed the vegetation and water quality in breeding and overwintering sites. The combination of these factors has had large influences on the decline of the Oregon Spotted frog.

 

Next

References:

Groom, M.J., Meffe, G.K. Carroll, C.R. (2005) Principles of Conservation Biology. (3rd edition) Sunderland, MA: Sinauer Associates Inc.

Hayes, Marc P., Engler, Joseph D., Van Leuven, Susan, Friesz, Daniel C., Quinn, Timothy, Pierce, John D. 2001. Overwintering of the Oregon Spotted Frog (Rana pretiosa)at Conboy Lake National Wildlife Refuge, Klickitat County, Washington, 2000-2001. Final Report. WDFW Olympis, Washington 39 p.

McKibben, Rene, Dushenko, William T., vanAggelen, Graham, Bishop, Christine A. 2008. The influence of water quality on the embryonic survivorship of the Oregon spotted frog (Rana pretiosa) in British Columbia, Canada. 395pp 28-40.

Pearl, Christopher A., Adams, Michael J. Leuthold, Niels. 2009. Breeding habitat and local population size of the Oregon spotted frog (Rana pretiosa) in Oregon, USA. Northwestern naturalist. 90 (2) pp 136-147.

Pearl, Christopher A., Hayes, Marc P. 2004. Habitat Association of the Oregon Spotted Frog (Rana pretiosa) A Literature review. Final Report. WDFW Olympia, Washington 44p.

Watson, James W., McAllister, Kelly A, Pierce, John D., Alvarado, Amy. 2000. Ecology of a Remnant Population of Oregon Spotted Frogs (Rana pretiosa) in Thurston County, Washington. Final Report. WDFE Olympia, Washington 85p.

Watson, James W., McAllister, Kelly R., Pierce, John D. 2003. Home ranges, movements, and habitat selection of Oregon spotted frog (Rana pretiosa)Journal of Herpetology. 37 (2) pp 292-300.

.