BioOne Complete (complete.BioOne.org) is a full-text database of 200 subscribed and open-access titles in the biological, ecological, and environmental sciences published by nonprofit societies, associations, museums, institutions, and presses.
The arrival of zebra mussels (Dreissena polymorpha (Pallas, 1771)) and subsequently quagga mussels (Dreissena bugensis Andrusov, 1897) (Dreissenidae) in the Great Lakes in the 1980s induced many changes, most notably the devastation of native freshwater mussel species. Recently, empty shells of the fragile papershell (Leptodea fragilis (Rafinesque, 1820)) have become common, particularly in the western basin of Lake Erie, suggesting that this fast-growing species may be increasing in numbers in the lake. To examine continued competition with dreissenids, shell age and length of L. fragilis were used to contrast lifespan and growth rate, estimated as the slope of age on shell length, for shells from two beach localities where byssal threads were present on most shells and two sites where dreissenids were rare or absent. Few recent shells from Lake Erie beaches exceeded 5 years of age, and byssal thread counts were more numerous on older shells. Growth and lifespan were estimated to be significantly lower where dreissenid mussels remained numerous than when measured either from historic collections along Lake Erie or from protected populations. Therefore, even for this early-reproducing species, competition from dreissenids may continue to interfere with growth and shorten lifespan, which are effects few other unionid species can likely tolerate sufficiently to sustain population growth.Résumé : L'arrivée des moules zébrées (Dreissena polymorpha (Pallas, 1771)) et, subséquemment, des moules quagga (Dreissena bugensis Andrusov, 1897) (dreissenidés) dans les Grands Lacs dans les années 1980 a induit de nombreux changements, dont le plus notable est la dévastation d'espèces de mulettes indigènes. Récemment, des coquilles vides de la leptodée fragile (Leptodea fragilis (Rafinesque, 1820)) sont devenues répandues, particulièrement dans le bassin occidental du lac Érié, donnant à penser que l'abondance de cette espèce à croissance rapide serait en expansion dans ce lac. Afin d'examiner la concurrence continue avec les dreissenidés, l'âge et la longueur de coquilles de L. fragilis ont été utilisés pour comparer la durée de vie et le taux de croissance, estimé comme étant la pente de l'âge par rapport à la longueur de la coquille, pour des coquilles provenant de deux sites de plage où des filaments de byssus étaient présents sur la plupart des coquilles et deux sites où les dreissenidés étaient rares ou absentes. Peu de coquilles récentes du lac Érié dépassaient l'âge de 5 ans, et le nombre de filaments de byssus était plus élevé sur les coquilles plus vieilles. Les estimations des taux de croissance et de la durée de vie étaient significativement plus faibles là où les dreissenidés demeuraient abondantes que dans des collections prélevées par le passé le long du lac Érié ou dans des populations protégées. Même pour cette espèce à reproduction précoce, la concurrence des dreissenidés pourrait donc continuer de nuire à la croissance et réduire la durée de vie, des effets que peu d'autres espèces d'unionidés peuvent vraisemb...
Optimal foraging theory explains that organisms whose foraging is as energetically efficient as possible should be favored by natural selection. However, many individuals must exhibit trade-offs between foraging and other factors in their environment (i.e., predation risk, competitive interactions). We present a hands-on activity for undergraduates using just a deck of cards, bingo chips, and dice to introduce ecological concepts of foraging theory, predator–prey interactions, and energy trade-offs. Specifically, this activity will focus on optimal foraging theory and giving-up density. Students should gain an understanding of how organisms balance predation risk and competitive interactions with energetic demands. Further, this activity can be scaled for nonmajors and introductory courses to introduce general ecological concepts, or for upper-division courses to explore advanced topics in foraging theory.
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