Seasonal comparison of community-level size-spectra in southern coalfield streams of West Virginia (USA)
2018
McGarvey, DanielJ. | Kirk, AndrewJ.
Inverse scaling relationships between average body mass (M) and density (D) have been reported in many lake and marine ecosystems but are less well documented in lotic systems. We used quantitative samples of benthic macroinvertebrate and fish D to model the D versus M (i.e., D ∞ 1/M) relationship in central Appalachian streams of the eastern USA. Specifically, we used the ataxic ‘size-spectra’ method (individuals identified only by size, not taxonomic identity, then aggregated within log₂ M bins) to model D as a function of M. Repeat samples were collected from three study streams in March, May, August, and October, allowing us to test for seasonal differences in the slopes and intercepts of size-spectra models, using linear mixed-effects modeling. Size-spectra slopes were significantly different among months, decreasing from March (slope = − 1.73) to May (− 1.81), then increasing to August (− 1.62) and October (− 1.65). Intercepts also differed among months but showed the opposite trend: intercepts increased from March (intercept = 0.51) to May (0.91), then decreased through August (0.44) and October (0.37). Size-spectra slopes and intercepts did not differ from the overall model parameters when estimated separately for macroinvertebrate and fish data. Finally, times series data on water temperature and discharge were used to show that size-spectra parameters may respond in predictable ways to the accumulation of degree days (i.e., the growing season) and to episodic flood events.
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