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Transcript
Jennifer Eagle Scientific Research Methods for Teachers Spring 2012 Human Alteration of Earth’s Ecosystems Habitat Fragmentation Source or Sink Habitats Alteration of the Natural Flow Regime Human Alteration of Earth’s Ecosystems Between one-third and one-half of the land surface has been transformed by human action (Vitousek et al. 1997). Humans have cleared land plots for: cropping, logging, grazing, urbanization, etc. Land transformation has become a primary force in the loss of biological diversity and is the single most important cause of extinction (Vitousek et al. 1997). Human Alteration of Earth’s Ecosystems: Habitat Fragmentation Native vegetation is removed or replaced with a crop leaving behind small patches of the original vegetation. The fragments of habitat that are left are likely to be in a less productive area (i.e., poorer soil, higher elevation, partially inundated) due to nonrandom clearing choices made by farmers (Laurance 2008). Fragmentation results in a reduction of the original habitat and chops up the remaining habitat into various sizes and degrees of isolation (Laurance 2008). Human Alteration of Earth’s Ecosystems: Habitat Fragmentation Fragmented habitats are reduced in size and are susceptible to edge effects: Changes in temperature Increased light Increased wind shear Increased predation This changes the species composition of the habitat area (Laurance 2008). Habitat Fragments: Sources or Sinks? Patches of land that are left behind are either habitat sources (high productivity), or habitat sinks (low productivity). Population size and growth rate may vary relative to habitat types that are available (Pulliam & Danielson 1991). Alteration of the Natural Flow Regime Land alterations have also resulted in an alteration of the natural hydrologic flow of river ecosystems. The clearing and/or drainage of land for agriculture generally results in increased overland flow, channel incision, floodplain isolation, and headward erosion of stream channels (Prestegaard 1988). Altering the natural flow can cause the degradation of aquatic and riparian habitats (Poff 1997). Alteration of the Natural Flow Regime Both high stream flows and low stream flows provide their own benefits to riverine species, however these benefits may only occur if the stream flow is allowed to fluctuate naturally. Altering stream flow disturbs the balance of species adaptations that are already in place, and forces organisms to relocate or adapt to a new flow regime. Swamp Rabbits (Sylvilagus aquaticus) Swamp rabbits are habitat specialists that live in the bottomland forests of the southeastern United States. They are at their northernmost reach in the Cache River Wetland. Swamp Rabbits (Sylvilagus aquaticus) Swamp rabbits tend to rest and feed in areas with canopy gaps (Zollner et al. 2000). Latrine sites, however, are more strongly correlated to the presence of downed logs (Zollner et al. 2000). Swamp rabbits have been known to use upland habitat during flooding of the bottomlands (Scharine et al. 2011). There is a concern for this species due to the fragmentation and loss of the forested bottomlands. Cache River Wetland CRW extends throughout four counties in Southern Illinois. It is comprised of forested wetlands, floodplains, upland forests, and limestone barrens (IDNR 2007). Much of the bottomlands were cleared for logging or farm land in the late 1800s. By the 1900s, the building of roads and other developments fragmented much of the remaining habitat. Since 1905, there have been nine major alterations of the natural drainage system to control flooding and drain wetland for farming including dredging, levees, dams, and channelization (IDNR 1997). Cache River Wetland: The Upper Cache and Lower Cache River The Post Creek Cutoff was built in 1915 to divert water from the Upper Cache River (UCR) to the Ohio River. This resulted in a split of the river, with the Lower Cache River (LCR) having a reduced flow by being cut off from its headwaters. Our Study Although there have been previous studies on swamp rabbit occupancy in southern Illinois, there has not been a comparison of habitat in the LCR vs. the UCR. Our objective is to determine if there is a difference in swamp rabbit occupancy in the LCR vs. the UCR. We hypothesize that there will be more swamp rabbits occupying the UCR due to a higher quantity and quality of suitable habitat there. Why would more swamp rabbits occupy the UCR than the LCR? A previous study (Rubert 2007) found more suitable swamp rabbit habitat in Union and Johnson Counties (263.73 km2) compared to Pulaski and Alexander Counties (176.75 km2). High flows maintain ecosystem productivity and diversity (Poff et al. 1997), and the flow to the LCR was dramatically reduced when it was cut off from the UCR in 1915. The LCR continues to accumulate excessive amounts of sediment and is consistently flooded. Our Methods We will find 10 suitable habitat areas in the UCR and LCR where known swamp rabbit populations exist, and place one artificial latrine log (ALL) at each site. We will examine the ALLs each day for 3 days and record the number of swamp rabbit fecal pellets on our data sheet. Data Analysis We will find the means of our artificial latrine log data in the UCR and LCR, and run a t-test. From our analysis and resulting p-value we will be able to determine if swamp rabbit occupancy rates are significantly higher in the UCR. Questions ???