Proceedings of the 18th Working Meeting of the Crocodile Specialist ...

Software limits allowed for simulating only an initial population of 30,000
individuals of all ages (i.e. as if only 1/3 of the total estimated individuals of C.
moreletii were thought to exist). Extinction was arbitrarily defined as only 500
individuals left (deliberately ignoring the fact that even such a small population might
well constitute a founding basis for an eventually needed recovery program).
The chosen scenario simulated high stress, including a steady progressive reduction
of carrying capacity (this is very improbable in reality, but of great help for getting
insight on population reactions to extreme pressure). Reduction of carrying capacity
was simulated as up to 75% in the 500-year lapse defined for the simulation of
population trajectory. With these parameters, five hundred iterations were run.
Potential catastrophes simulated included: a) transcendent habitat deterioration (p =
0.10 for the lapse), and b) transcendent reduction of prey base (p = 0.15 for the lapse).
Parameters considered: no inbreeding depression assumed to occur, on the basis of
current evidence. First age of reproduction for males and females, 8 years; maximum
breeding age (senescence), 30 years; sex ratio at birth (slightly biased towards males,
based on COPAN findings), 60%; polygynous mating; 41.3% of adult males assumed
successful in having descendence (more field data are needed); 80% percent adult
females assumed as breeding (more field data needed). Of those females producing
progeny: mean number of progeny per breeding female per year = 30 ± 5.
After the 500 year-lapse we simulated, the estimated probability of extinction was
0.1380 ± 0.015. Seen as the inverse, 0.86% probability of survival was obtained.
Throughout the 500 runs (500 years each) and with an initial population of 30,000
individuals, none of the end populations went below 4,500 individuals. These results
are consistent with a high elasticity of the species, as actually demonstrated by its
spontaneous comeback after 30 years of hunting ban in Mexico (no significant
reintroductions or population supplementation has been attempted). Nevertheless, we
emphasize that more data on the actual breeding pool will be needed to gain more
insight through modelling. The main product of modelling is progressively improving
diagnostics, not arriving to rigid, final numbers (see the following graphics; Figure 5).
Modelling also considered that high heterozygosity has been documented for C.
moreletii in northern Belize (H = 0.49; Dever et al., 2002); this is higher than that
documented for Alligator mississipiensis (H = 0.46; Glenn et al., 1998). A relatively
high index of inter-population migration has been documented in Belize (Nm = 5.15;
Dever et al, 2002). Minimal individual movement can contribute to genetic diversity
by panmyxis (Wright, 1931). With current evidence, no genetic bottlenecks would be
anticipated for the near future.
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