Academic literature on the topic 'False map turtles'

We investigated how environmental gradients measured along the St. Croix River in Minnesota and Wisconsin, U.S.A., influenced the turtle assemblage. Among seven species, the five most common species were generalists and had wide distributions throughout the study area. However, patterns in assemblage structure were related to environmental gradients along the river. Sex ratios were male-dominated for the five most common species, and few or no juveniles were captured during the study. The first two canonical axes of a canonical correspondence analysis accounted for 92.7% of the variation in species-environment gradients. Most of the variation in distribution and abundance was attributed to gradients in channel morphology and physical characteristics along the river channel. Abundances of common snapping (Chelydra serpentina), false map (Graptemys pseudogeographica), and painted (Chrysemys picta bellii) turtles were associated with muck substrates and the number of basking sites (i.e., snags, rocks), which increased farther downstream. Abundance of spiny softshell turtles was closely related to increased water velocity and depth, which were related to hydraulic control points in the river. Abundance of common map turtles was associated with the presence of open sandy areas, uniform channel bottom, and gravel substrates. Geomorphic changes along the St. Croix River clearly influence the turtle assemblage and these specific relations should be considered in efforts to preserve and restore components of the assemblage.

Abstract Turtles are linked to energetic food webs as both consumers of plants and animals and prey for many species. Turtle biomass in freshwater systems can be an order of magnitude greater than that of endotherms. Therefore, declines in freshwater turtle populations can change energy transfer in freshwater systems. Here we report on a mark–recapture study at a lake and adjacent borrow pit in a relict tract of bottomland hardwood forest in the Mississippi River floodplain in southeast Missouri, which was designed to gather baseline data, including sex ratio, size structure, and population size, density, and biomass, for the freshwater turtle population. Using a variety of capture methods, we captured seven species of freshwater turtles (snapping turtle Chelydra serpentina; red-eared slider Trachemys scripta; southern painted turtle Chrysemys dorsalis; river cooter Pseudemys concinna; false map turtle Graptemys pseudogeographica; eastern musk turtle Sternotherus odoratus; spiny softshell Apalone spinifera) comprising four families (Chelydridae, Emydidae, Kinosternidae, Trinoychidae). With the exception of red-eared sliders, nearly all individuals captured were adults. Most turtles were captured by baited hoop-nets, and this was the only capture method that caught all seven species. The unbaited fyke net was very successful in the borrow pit, but only captured four of the seven species. Basking traps and deep-water crawfish nets had minimal success. Red-eared sliders had the greatest population estimate (2,675), density (205/ha), and biomass (178 kg/ha). Two species exhibited a sex-ratio bias: snapping turtles C. serpentina in favor of males, and spiny softshells A. spinifera in favor of females.

Damming and sand mining are examples of factors that indirectly damage or destroy populations of river turtles. Direct factors such as human exploitation are typically more obvious causes of population decline and often serve as stimuli to incite conservation action by a concerned public or government. While direct factors typically kill animals outright or at least remove them from the gene pool, indirect factors can surreptitiously reduce their chances for survival by altering habitat or reducing food supplies. As such, they may decimate a population before it becomes obvious that something is wrong. Though less conspicuous than the direct causes, indirect factors are at least of equal importance in determining the ultimate survival of a species. Table 6.1 summarizes the types of indirect factors affecting selected species. Two important types of indirect factors, habitat alteration and species introduction, are discussed below. Habitat alteration implies any change in an animal’s environment, but herein we will consider human or anthropogenic alterations. Anthropogenic habitat changes are not necessarily harmful to every type of turtle. Riverine specialists are more vulnerable to such changes than are eurytopic generalists that occupy a variety of lotic and lentic habitats. Generalists are by their nature adaptable and thus are less likely to be harmed by changing conditions. A study by D. Moll (1980) on the Illinois River illustrates this principle well. The original environment of the Illinois River has been greatly altered as a result of clearing and draining land for agriculture, dumping of municipal sewage (particularly by the Chicago Sanitary District), and the construction of a series of locks and dams by the Corps of engineers to facilitate barge traffic. Moll found that while these alterations had reduced or eliminated populations of Blanding’s turtles, yellow mud turtles and smooth softshells, generalist species such as the common slider, false map turtles, spiny softshells and common snapping turtles were thriving in the altered environment (see also Mills et al, 1966; Bellrose et al., 1977). Similarly, Anderson (1965) reported that commercial fishermen of the Mississippi and Missouri Rivers noted increases in softshells (spiny?) and snappers in areas having moderate sewage pollution.