TY - JOUR
T1 - Population dynamics of brown trout (Salmo trutta) in Spruce Creek Pennsylvania
T2 - A quarter-century perspective
AU - Grossman, Gary D.
AU - Carline, Robert F.
AU - Wagner, Tyler
N1 - Funding Information:
We are grateful to our families for their constant support. This study was partially supported by the Pennsylvania State University, the Pennsylvania Game and Fish Commission and the Warnell School of Forestry and Natural Resources. We are grateful for the support of our families and technical staff and GG obtained creative support from Jittery Joe's and Two Story. Troy Simon aided with quantitative analyses. An earlier version of the ms. was improved by the comments of B. Bozeman, K. Chernoff, J. Cullen, J. Lobon-Cervia, J. Martin, and T. Simon. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.
Publisher Copyright:
© 2017 John Wiley & Sons Ltd
PY - 2017/7
Y1 - 2017/7
N2 - We examined the relationship between density-independent and density-dependent factors on the demography of a dense, relatively unexploited population of brown trout in Spruce Creek Pennsylvania between 1985 and 2011. Individual PCAs of flow and temperature data elucidated groups of years with multiple high flow versus multiple low flow characteristics and high versus low temperature years, although subtler patterns of variation also were observed. Density and biomass displayed similar temporal patterns, ranging from 710 to 1,803 trout/ha and 76–263 kg/ha. We detected a significantly negative linear stock-recruitment relationship (R2 =.39) and there was no evidence that flow or water temperature affected recruitment. Both annual survival and the per-capita rate of increase (r) for the population varied over the study, and density-dependent mechanisms possessed the greatest explanatory power for annual survival data. Temporal trends in population r suggested it displayed a bounded equilibrium with increases observed in 12 years and decreases detected in 13 years. Model selection analysis of per-capita rate of increase data for age 1, and adults (N = eight interpretable models) indicated that both density-dependent (five of eight) and negative density-independent processes (five of eight, i.e. high flows or temperatures), affected r. Recruitment limitation also was identified in three of eight models. Variation in the per-capita rate of increase for the population was most strongly affected by positive density independence in the form of increasing spring–summer temperatures and recruitment limitation. Model selection analyses describing annual variation in both mean length and mass data yielded similar results, although maximum wi values were low ranging from 0.09 to 0.23 (length) and 0.13 to 0.22 (mass). Density-dependence was included in 15 of 15 interpretable models for length and all ten interpretable models for mass. Similarly, positive density-independent effects in the form of increasing autumn–winter flow were present in seven of 15 interpretable models for length and five of ten interpretable models for mass. Negative density independent effects also were observed in the form of high spring–summer flows or temperatures (N = 4), or high autumn–winter temperatures (N = 1). Our analyses of the factors affecting population regulation in an introduced population of brown trout demonstrate that density-dependent forces affected every important demographic characteristic (recruitment, survivorship, the rate of increase, and size) within this population. However, density-independent forces in the form of seasonal variations in flow and temperature also helped explain annual variation in the per-capita rate of increase, and mean length and mass data. Consequently, population regulation within this population is driven by a complex of biotic and environmental factors, although it seems clear that density-dependent factors play a dominant role.
AB - We examined the relationship between density-independent and density-dependent factors on the demography of a dense, relatively unexploited population of brown trout in Spruce Creek Pennsylvania between 1985 and 2011. Individual PCAs of flow and temperature data elucidated groups of years with multiple high flow versus multiple low flow characteristics and high versus low temperature years, although subtler patterns of variation also were observed. Density and biomass displayed similar temporal patterns, ranging from 710 to 1,803 trout/ha and 76–263 kg/ha. We detected a significantly negative linear stock-recruitment relationship (R2 =.39) and there was no evidence that flow or water temperature affected recruitment. Both annual survival and the per-capita rate of increase (r) for the population varied over the study, and density-dependent mechanisms possessed the greatest explanatory power for annual survival data. Temporal trends in population r suggested it displayed a bounded equilibrium with increases observed in 12 years and decreases detected in 13 years. Model selection analysis of per-capita rate of increase data for age 1, and adults (N = eight interpretable models) indicated that both density-dependent (five of eight) and negative density-independent processes (five of eight, i.e. high flows or temperatures), affected r. Recruitment limitation also was identified in three of eight models. Variation in the per-capita rate of increase for the population was most strongly affected by positive density independence in the form of increasing spring–summer temperatures and recruitment limitation. Model selection analyses describing annual variation in both mean length and mass data yielded similar results, although maximum wi values were low ranging from 0.09 to 0.23 (length) and 0.13 to 0.22 (mass). Density-dependence was included in 15 of 15 interpretable models for length and all ten interpretable models for mass. Similarly, positive density-independent effects in the form of increasing autumn–winter flow were present in seven of 15 interpretable models for length and five of ten interpretable models for mass. Negative density independent effects also were observed in the form of high spring–summer flows or temperatures (N = 4), or high autumn–winter temperatures (N = 1). Our analyses of the factors affecting population regulation in an introduced population of brown trout demonstrate that density-dependent forces affected every important demographic characteristic (recruitment, survivorship, the rate of increase, and size) within this population. However, density-independent forces in the form of seasonal variations in flow and temperature also helped explain annual variation in the per-capita rate of increase, and mean length and mass data. Consequently, population regulation within this population is driven by a complex of biotic and environmental factors, although it seems clear that density-dependent factors play a dominant role.
UR - http://www.scopus.com/inward/record.url?scp=85020292611&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=85020292611&partnerID=8YFLogxK
U2 - 10.1111/fwb.12932
DO - 10.1111/fwb.12932
M3 - Article
AN - SCOPUS:85020292611
SN - 0046-5070
VL - 62
SP - 1143
EP - 1154
JO - Freshwater Biology
JF - Freshwater Biology
IS - 7
ER -