Literaturdatenbank
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Bondi, C. A. (2009). A comparison of western pond turtle (actinemys marmorata) movements in perennial and intermittent portions of a northwestern california river system. Unpublished thesis Masters, Humboldt State University.
Added by: Admin (21 Nov 2009 11:53:06 UTC) |
| Resource type: Thesis/Dissertation BibTeX citation key: Bondi2009 View all bibliographic details  |
Categories: General Keywords: Actinemys, Actinemys marmorata, Emydidae, Habitat = habitat, Nordamerika = North America, Schildkröten = turtles + tortoises Creators: Bondi Publisher: Humboldt State University |
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| Abstract |
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Actinemys marmorata Many turtle species require aquatic and terrestrial habitats during different times in their life history for foraging, mating, nesting, estivation and overwintering. The status of many turtle populations depends directly on the condition of both environments, as well as the connectivity between the two. Identifying factors that prompt movements between these two environments, or conditions in which one is no longer suitable such as the occurrence of seasonal drying, can aid in predictions on migration timing and habitat patch occupancy. This information in turn can be used in conscious land planning decisions. I used radiotelemetry to track the seasonal movements of Western Pond turtles inhabiting perennial and intermittent river reaches of the Mad River drainage in northwestern California. I monitored several environmental characteristics such as water and air temperature, and water availability to describe migrations in the context of changing environmental conditions. In addition, I investigated the effects that seasonal drying may have on adult body size by comparing the carapace length and body mass of individuals captured at both reaches. I found that while differences in water availability did not significantly affect the extent of turtle movements within aquatic and terrestrial environments, it did affect migration timing. Turtles in the intermittent reach departed the river earlier than those in the perennial reach, apparently in response to declines in surface water area. In the perennial reach, the turtles appeared to depart the river in response to declining air and water temperatures, as well as rises in streamflow. In response to declining water availability, 100% of turtles at the intermittent site estivated in adjacent upland habitat in 2007, and 92% of them did so in 2008; this indicates that this is the dominant strategy for dealing with drying conditions in this population. Turtles from the intermittent reach also migrated to the river earlier in the spring than those in the perennial reach, perhaps in an attempt to maximize foraging opportunities before the severe water loss that occurs mid-summer. Turtles were significantly smaller with regards to both carapace length and body mass at the intermittent reach, suggesting a morphological population response to the extreme conditions associated with seasonal drying. This research shows that loss of surface water influences the movement patterns of Western Pond turtles by eliciting an emigration response, and also appears to affect the body size of adult turtles. This result has important conservation implications since it demonstrates that available water may influence the body size of adults, which may have negative affects on survival and fecundity. Anthropogenic induced declines in available surface water due to pond draining for agricultural purposes, water diversions and intermittent flows created by dams, can all result in a depletion of aquatic resources and create aquatic environments unsuitable for resident turtles. Land managers need to evaluate individual populations’ response to decreasing water to develop management plans that alleviate any negative impacts.
Added by: Admin |