Re‐evaluating the effect of harvesting regimes on Nile crocodiles using an integral projection model

• Published in: The Journal of animal ecology Vol. 82; no. 1; pp. 155 - 165
• Main Authors: Wallace, Kevin, Leslie, Alison, Coulson, Tim, Boots, Mike
• Format: Journal Article
• Language: English
• Published: Oxford Blackwell Publishing 2013; Blackwell; Blackwell Publishing Ltd
• Subjects: Alligators and Crocodiles; Alligators and Crocodiles - physiology; Amphibia. Reptilia; Animal and plant ecology; Animal ecology; Animal, plant and microbial ecology; Animals; Aquatic reptiles; Biological and medical sciences; Body Size; Breeding; Conservation biology; Crocodiles; Crocodylus niloticus; Ecological modeling; eggs; Female; Female animals; fertility selection; Fundamental and applied biological sciences. Psychology; General aspects; harvesting; integrated pest management; Mathematical independent variables; Models, Biological; Nile crocodile; physiology; Population Dynamics; Population ecology; population growth; Population parameters; Population size; sensitivity analysis; Vertebrates: general zoology, morphology, phylogeny, systematics, cytogenetics, geographical distribution; Vertebrata; Population growth; Sensitivity analysis; Fertility; Nile crocodile; Crocodilia; Reptilia; Models; Crocodylus niloticus; fertility selection
• ISSN: 0021-8790; 1365-2656; 1365-2656
• DOI: 10.1111/j.1365-2656.2012.02027.x

Crocodile populations are size‐structured, and for populations that are subject to harvesting, removal is typically size selective. For this reason, size‐structured matrix models are typically used to analyse the dynamics of crocodile populations. The boundaries between the size classes used to classify individuals in these models are typically chosen arbitrarily. This is problematic because results can depend upon the number and width of size classes. The recent development of continuous character population models termed integral projection models (IPM) has removed the need to arbitrarily classify individuals. These models are yet to be applied to harvested animal populations. Using information obtained from the literature, we develop an IPM for crocodiles. We use perturbation analyses to investigate how altering size‐specific demographic rates influences the population growth rate and the strength of selection on snout to vent length. We find that perturbations can lead to complex responses. Sensitivity analysis to population growth and fertility selection reveals that the smallest animals and the sizes of early breeding individuals and their eggs may have more influence on these population biology parameters than previously thought. Although our model is relatively simple, our results show that IPM can be used to gain theoretical insight into the possible consequences of altering size‐specific demographic rates on the population and evolutionary ecology of harvested populations.