title: Shift in a large river fish assemblage: body-size and trophic structure dynamics.
abstract: As the intensity and speed of environmental change increase at both local and global scales it is imperative that we gain a better understanding of the ecological implications of community shifts. While there has been substantial progress toward understanding the drivers and subsequent responses of community change (e.g. lake trophic state), the ecological impacts of food web changes are far less understood. We analyzed Wabash River fish assemblage data collected from 1974-2008, to evaluate temporal variation in body-size structure and functional group composition. Two parameters derived from annual community size-spectra were our major response variables: (1) the regression slope is an index of ecological efficiency and predator-prey biomass ratios, and (2) spectral elevation (regression midpoint height) is a proxy for food web capacity. We detected a large assemblage shift, over at least a seven year period, defined by dramatic changes in abundance (measured as catch-per-unit-effort) of the dominant functional feeding groups among two time periods; from an assemblage dominated by planktivore-omnivores to benthic invertivores. There was a concurrent increase in ecological efficiency (slopes increased over time) following the shift associated with an increase in large-bodied low trophic level fish. Food web capacity remained relatively stable with no clear temporal trends. Thus, increased ecological efficiency occurred simultaneous to a compensatory response that shifted biomass among functional feeding groups.
authors.affiliation: Institute for Great Lakes Research, Biology Dept., Central Michigan University, Mount Pleasant, MI 48858, United States of America.
authors.forename: Kyle J
authors.initials: KJ
authors.lastname: Broadway
authors.affiliation: Department of Biology, Ball State University, Muncie, IN 47306, United States of America.
authors.forename: Mark
authors.initials: M
authors.lastname: Pyron
authors.affiliation: Department of Biology, DePauw University, Greencastle, IN 46135, United States of America.
authors.forename: James R
authors.initials: JR
authors.lastname: Gammon
authors.affiliation: Institute for Great Lakes Research, Biology Dept., Central Michigan University, Mount Pleasant, MI 48858, United States of America.
authors.forename: Brent A
authors.initials: BA
authors.lastname: Murry
mesh_terms: D000818:Animals; D049628:Body Size; D005247:Feeding Behavior; D005399:Fishes / Q000033:anatomy & histology* / Q000502:physiology*; D020387:Food Chain; D025341:Principal Component Analysis; D045483:Rivers; D013045:Species Specificity; D013997:Time Factors