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. 2017 Dec 12;8(2):928-934.
doi: 10.1002/ece3.3658. eCollection 2018 Jan.

Minimum area thresholds for rattlesnakes and colubrid snakes on islands in the Gulf of California, Mexico

Jesse M Meik  1 , Robert Makowsky  2   3
Affiliations

Minimum area thresholds for rattlesnakes and colubrid snakes on islands in the Gulf of California, Mexico

Jesse M Meik et al. Ecol Evol. .

Abstract

We expand a framework for estimating minimum area thresholds to elaborate biogeographic patterns between two groups of snakes (rattlesnakes and colubrid snakes) on islands in the western Gulf of California, Mexico. The minimum area thresholds for supporting single species versus coexistence of two or more species relate to hypotheses of the relative importance of energetic efficiency and competitive interactions within groups, respectively. We used ordinal logistic regression probability functions to estimate minimum area thresholds after evaluating the influence of island area, isolation, and age on rattlesnake and colubrid occupancy patterns across 83 islands. Minimum area thresholds for islands supporting one species were nearly identical for rattlesnakes and colubrids (~1.7 km2), suggesting that selective tradeoffs for distinctive life history traits between rattlesnakes and colubrids did not result in any clear advantage of one life history strategy over the other on islands. However, the minimum area threshold for supporting two or more species of rattlesnakes (37.1 km2) was over five times greater than it was for supporting two or more species of colubrids (6.7 km2). The great differences between rattlesnakes and colubrids in minimum area required to support more than one species imply that for islands in the Gulf of California relative extinction risks are higher for coexistence of multiple species of rattlesnakes and that competition within and between species of rattlesnakes is likely much more intense than it is within and between species of colubrids.

Keywords: Baja California; Crotalus; extinction risks; insular dwarfism; interspecific competition; island biogeography.

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Figures

Figure 1
Figure 1
Diagram of hypothetical patterns that result from comparisons of minimum area thresholds for supporting single species (squares) and two species (circles) between two taxonomic groups (blue and orange). Differences in minimum area thresholds for supporting single species imply differences in ecological (energetic) efficiency and/or carrying capacity per unit area, whereas differences in minimum area thresholds for supporting coexisting species imply stronger competitive interactions within and between species of a group
Figure 2
Figure 2
Map of western Mexico, including the Baja California Peninsula and Gulf of California. The shape outlined with dashed lines indicates the study region (islands of the western Gulf of California)
Figure 3
Figure 3
Empirical estimates of minimum area thresholds for supporting single species were nearly identical for rattlesnakes and colubrid snakes (1.8 vs. 1.7 km2, respectively), but area estimates for supporting two or more species of rattlesnakes were over five times greater than for colubrids (37.1 vs. 6.7 km2, respectively). Photographs depict an Angel de la Guarda speckled rattlesnake (Crotalus angelensis; top) and a California night snake (Hypsiglena ochrorhyncha; bottom), both from Angel de la Guarda Island
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