The role of density-dependent individual growth in the persistence of freshwater salmonid populations |
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Authors: | Simone Vincenzi Alain J Crivelli Dusan Jesensek Giulio A De Leo |
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Institution: | (1) Dipartimento di Scienze Ambientali, Università degli Studi di Parma, Viale G. P. Usberti 33/A, 43100 Parma, Italy;(2) Station Biologique de la Tour du Valat, Le Sambuc, 13200 Arles, France;(3) Tolmin Angling Association, Modrej 26a, 65216 Most na Soci, Slovenia;(4) Dipartimento di Scienze Ambientali, Università degli Studi di Parma, Viale G. P. Usberti 11/A, 43100 Parma, Italy |
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Abstract: | Theoretical and empirical models of populations dynamics have paid little attention to the implications of density-dependent
individual growth on the persistence and regulation of small freshwater salmonid populations. We have therefore designed a
study aimed at testing our hypothesis that density-dependent individual growth is a process that enhances population recovery
and reduces extinction risk in salmonid populations in a variable environment subject to disturbance events. This hypothesis
was tested in two newly introduced marble trout (Salmo marmoratus) populations living in Slovenian streams (Zakojska and Gorska) subject to severe autumn floods. We developed a discrete-time
stochastic individual-based model of population dynamics for each population with demographic parameters and compensatory
responses tightly calibrated on data from individually tagged marble trout. The occurrence of severe flood events causing
population collapses was explicitly accounted for in the model. We used the model in a population viability analysis setting
to estimate the quasi-extinction risk and demographic indexes of the two marble trout populations when individual growth was
density-dependent. We ran a set of simulations in which the effect of floods on population abundance was explicitly accounted
for and another set of simulations in which flood events were not included in the model. These simulation results were compared
with those of scenarios in which individual growth was modelled with density-independent Von Bertalanffy growth curves. Our
results show how density-dependent individual growth may confer remarkable resilience to marble trout populations in case
of major flood events. The resilience to flood events shown by the simulation results can be explained by the increase in
size-dependent fecundity as a consequence of the drop in population size after a severe flood, which allows the population
to quickly recover to the pre-event conditions. Our results suggest that density-dependent individual growth plays a potentially
powerful role in the persistence of freshwater salmonids living in streams subject to recurrent yet unpredictable flood events.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Compensatory responses Flood disturbance Marble trout Population dynamics Resilience |
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