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Lindeman, P. V. (1997). Effects of competition, phylogeny, ontogeny, and morphology on structuring the resource use of freshwater turtles. Unpublished thesis , Univerity of Louisville, Louisville, Kentucky. 
Added by: Admin (06 Jan 2014 18:24:49 UTC)
Resource type: Thesis/Dissertation
BibTeX citation key: anon1997b
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Categories: General
Keywords: Apalone mutica, Emydidae, Graptemys geographica, Graptemys ouachitensis, Graptemys pseudogeographica, Habitat - habitat, Nordamerika - North America, Pseudemys concinna, Schildkröten - turtles + tortoises, Trachemys scripta, Trionychidae, Verhalten - ethology
Creators: Lindeman
Publisher: Univerity of Louisville (Louisville, Kentucky)
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Abstract     
Three studies were conducted to assess the importance of cornpetition, phylogeny, ontogeny, and morphology in str~cturing resource use in assemblages of freshwater turtles: 1) Resource use with respect to habitat, diet, and diel and seasonal use of basking time, was quantified for five turtle species microsympatric in a cove on Kentucky Lake, an irnpoundment of the lower Tennessee River. Pseudocornmunity analyses were conducted to test for significant structure in resource use, and morphological characteristics were measured and related to resource use. Intraspecific patterns of resource use also were studied. 2) The evolution of the relative width of the head and alveolar surfaces in the diverse genus Graptemys was studied. 3) Aggressive interactions among turtles in the assemblage in Kentucky Lake were quantified. Cornpetition was shown to be of little irnportance in structuring resource use in Kentucky Lake. Instead, phylogeny and historical use of resources (i.e., in unirnpounded habitats) appeared to be the most important influences on resource use. Three strictly riverine species with relatively long limbs and digits (Graptemys pseudogeographica, G. ouachitensis, and Apalone mutica) used outer portions of the cove near deeper waters to a greater extent than did two shorter-limbed species which inhabit both lotie and lentie wa~e=s (Trachemys scripta and Pseudemys concinna). Only the difference in habitaL between A. mutica and the other tour speeies was shown to be signifieant in pseudoeommunity analysis, a result whieh ean be better explained by differenees ln basking substrates than by eompetition. Dietary studies indieated two guilds, omnivore and algivore, in spiLe of low pairwise overlap values that resulLed fro~ overall prey diversity. Fnalysis of use of diel and seasonal basking time revealed signifieant strueture (partitioning) at only the rank of seeond-nearest neighbor for seasonal time. Intraspecific analyses of habitat use and diet suggested that relative body size was the most important influence on intraspeeifie resouree use. Biologists have long noted a diehotomy in relative head width and alveolar width among speeies of map tULtles (Graptemys) , partieularly with regard to adult females. I measured plastron length (PL), head width (HW) , and alveolar width (AW) of pearly 2300 speeimens representing the 12 reeognized species and used allometrie regressions to investigate this genus as examples of a) sexual dimorphism in trophie morphology and b) replieate adaptive radiation. Sexual dimorphism was noted in HW as a function of PL, with females of male sizes having wider heads, but AW as a funetion of HW was not dimorphie. Sexual differenees in HW probably are related to the dimorphie niehes of Graptemys. Based on predicted HW at maximum PL in adult females, species were determined to be mega-, meso-, or microcephalic. Distributions of Graptemys species in sympatry and allopatry revealed patterns consistent with structuring of distributions via competitive interactions. Superimposing data on relative HW onto a phylogeny of the genus suggests there was, at most, a single episode of character displacement, with subsequent character assortment, in Graptemys evolution. In 100.7 hours of observation, 123 aggressive interactions during basking were recorded. The rate of 1.2 aggressive interactions/hour is low compared with published studies, supporting the contention that little competition for basking space occurred. No consistent advantage during interactions was noted for any of the four species. Larger turtles won 74% of all interactions, and initiators won 84%; in all, 65% were won by larger, initiating turtles. Larger turtles were more likely to displace smaller turtles into the water, and elicited avoidance behaviors from smaller turtles that were never elicited from larger turtles by smaller turtles. The hypothesis that smaller turtles assess and avoid larger turtles is suggested by the lower rate of initiation by smaller turtles, the frequent turning away response that was observed only in smaller turtles, and the fact that smaller turtles voluntarily displaced themselves when larger turtles emerged from the water or advanced toward them on a substrate. Larger turtles were not observed to react similarly in converse situations. Competition did not appear to influence resource use in the assemblage of five species studied, but competitive exclusion may have been important in determining the success of invasion of new river drainages by Grapternys species. Competitive exclusion mayaIso be responsible for the absence of some turtle species from the study area on Kentucky Lake, in particular Grapternys geographica, which has atrophie morphology and diet similar to that of the resident G. pseudogeographica.
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