Ecological Archives E095-022-A6

John F. Benson, Brent R. Patterson, Peter J. Mahoney. 2014. A protected area influences genotype-specific survival and the structure of a Canis hybrid zone. Ecology 95:254–264. http://dx.doi.org/10.1890/13-0698.1

Appendix F. Secondary roads × eastern wolf: supporting analysis.

To ensure that the importance of the eastern wolf × secondary road density interaction was not unduly influenced by data from any individual mortality event, we sequentially removed data from each resident eastern wolf that died during the study (n = 10). For these supporting analyses, we included all variables retained in the top model (i.e., deer availability, secondary road density, 2010, and the eastern wolf × secondary road density interaction) and ran 10 separate models. We excluded data from a different eastern wolf mortality from each model and re-assessed the significance of the eastern wolf × secondary road density interaction. Next, for each of these 10 models, we changed the reference group from all other (non-eastern wolf) genotypes to eastern wolf to examine significance tests between eastern wolves and each of the other genotypes individually (i.e., coyotes, eastern wolf × coyote hybrids, and admixed gray wolves).

The results did not change appreciably except when we removed the eastern wolf whose home range had the highest secondary road density (EW10, Table F). Data from this individual clearly influenced on the results. That the most extreme data-point would influence the results of an analysis with a relatively small number of mortalities was not surprising. However, even with data from this individual excluded, eastern wolves still survived marginally significantly worse than all other Canis types combined (P> = 0.060) in relation to increased secondary road density. Specifically, eastern wolves survived marginally significantly worse than coyotes (P> = 0.053), eastern wolf × coyote hybrids (P> = 0.091), and admixed gray wolves (P> = 0.091) in relation to increasing secondary road density (Table F1). Thus, even though the importance and significance of this interaction as influenced by data from EW10, the importance of the interaction remained and the results were still marginally significant.

Studying survival of rare species often results in smaller sample sizes and lower statistical power than desirable under optimal circumstances. Despite the relatively low sample size of eastern wolves, we have clearly sampled a high proportion of resident wolves and coyotes in my study units (Appendix B). Thus, the sample size may be low from the perspective of optimal statistical power, but should be representative of the survival capabilities of the different Canis types in and adjacent to APP. Therefore, our results represent valuable information for understanding hybridization dynamics in the APP hybrid zone and for developing conservation strategies for eastern wolves.

Table F1. Significance of genotype × secondary road density interactions when survival data from individual eastern wolves that died (n = 10) were excluded from analyses. For each eastern wolf mortality excluded I show: road densities within the home range of the excluded wolf and P values from comparison of eastern wolf survival with: all other genotypes combined (All), coyotes (vs. Coyotes), coyotes × eastern wolves (vs.Coyote × EW), and admixed gray wolves (vs. Admixed GW). In all cases eastern wolf survival was lower than other Canis types, either significantly (P < 0.05) or marginally significantly (0.05 < P < 0.10).

Wolf

2° Rd Density

All

vs. Coyotes

vs. Coyote × EW

vs. Admixed GW

EW1

0.00

<0.001

<0.001

<0.001

0.011

EW2

<0.01

<0.001

<0.001

<0.001

0.012

EW3

0.04

<0.001

<0.001

<0.001

0.015

EW4

0.07

<0.001

<0.001

<0.001

0.024

EW5

0.10

<0.001

<0.001

<0.001

0.011

EW6

0.13

<0.001

<0.001

   0.002

0.017

EW7

0.14

<0.001

<0.001

0.001

0.018

EW8

0.23

<0.001

<0.001

0.003

0.029

EW9

0.29

<0.001

<0.001

0.004

0.029

EW10

0.53

0.060

0.053

0.091

0.091


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