ESR 6:25-39 (2008)  -  DOI: https://doi.org/10.3354/esr00119

Relative importance of natural disturbances and habitat degradation on snail kite population dynamics

Julien Martin1, 2, 3,*, Wiley M. Kitchens1, 2, Christopher E. Cattau1, 2, Madan K. Oli2

1Florida Cooperative Fish and Wildlife Research Unit, Building 810, University of Florida, Gainesville, Florida 32611-0485, USA
2Department of Wildlife Ecology and Conservation, University of Florida, Gainesville, Florida 32611-0485, USA
3Patuxent Wildlife Research Center, United States Geological Survey, 12100 Beech Forest Road, Laurel, Maryland 20708, USA

ABSTRACT: Natural disturbances and habitat degradation are major factors influencing the dynamics and persistence of many wildlife populations, yet few large-scale studies have explored the relative influence of these factors on the dynamics and persistence of animal populations. We used long-term demographic data and matrix population models to examine the potential effects of habitat degradation and natural disturbances on the dynamics of the endangered snail kite Rostrhamus sociabilis in Florida, USA. We found that estimates of stochastic population growth rate were low (0.90). Population growth rate (λ) during the first half or our study period (1992 to 1998) was substantially greater than during the second half (1999 to 2005). These 2 periods were characterized by contrasting hydrological conditions. Although λ was most sensitive to changes in adult survival, the analysis of life table response experiments revealed that a reduction in fertility of kites accounted for >80% of the observed decline in population growth rate. We examined the possibility that the reduction in λ was caused by (1) habitat degradation due to management, (2) an increase in frequency of moderate drying events in recent years; and (3) both habitat degradation and an increase in frequency of moderate drying events. Our results suggest that both factors could potentially contribute to a large decrease in population growth rate. Our study highlights the importance of simultaneously considering short- and long-term effects of disturbances when modeling population dynamics. Indeed, focusing exclusively on one type of effect may be misleading to both our understanding of the ecological dynamics of the system and to management. The relevance of our results to management is heightened because the snail kite has been selected as a key performance measure of one of the most ambitious ecosystem restoration projects ever undertaken.


KEY WORDS: Matrix population models · Life table response experiment · Everglades restoration · Fecundity · Catastrophes


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Cite this article as: Martin J, Kitchens WM, Cattau CE, Oli MK (2008) Relative importance of natural disturbances and habitat degradation on snail kite population dynamics. Endang Species Res 6:25-39. https://doi.org/10.3354/esr00119

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