Social and Spatial Structure of Male-Female Interactions in Gopher Tortoises, Gopherus Polyphemus
Social network analyses are sparse, despite having great potential to illuminate intricate details of wildlife behavioral ecology and to inform basic conservation practices. Using social interactions recorded during 1 year of 5-second interval photography, we conducted social network analyses of Gopher Tortoises (Gopherus polyphemus). G. polyphemus are charismatic and declining mid-sized tortoises that are habitat specialists endemic to the southeastern United States. We also conducted a simultaneous radio-telemetric study of tortoises contained within our study population to ascertain whether home range location is consistent with membership in distinct tortoise social network communities. We found strong statistical support for the presence of nonrandom social networks that were derived from male-female mating relationships. The most parsimonious social network included two distinct “cliques” that were spatially segregated. Each clique contained a similar number of males and females. Understanding this basic aspect of tortoise behavior should be key in basic population biology, not only of turtles but also other reptiles. Our results should influence protocols for successful conservation of this keystone species.Abstract
Number and type of noncoincidental social interactions recorded for each tortoise observed. The interaction types are: noncontact (e.g., the tortoise oriented physically toward another tortoise, the tortoise was visually signaling another tortoise via head bobbing, etc.), physical contact with another tortoise (but not mounting), mounting another tortoise, and sharing a burrow overnight with another tortoise.
The spatial structure of the male-on-female mounting social network. The shaded regions represent the pooled 95% kernel home range of male tortoises in each clique. Square markers indicate locations of burrows monitored by camera traps. Locations of additional burrows used by females in each clique are indicated by markers. The habitat in which each clique lives is one continuous sand ridge that is managed the same throughout, with no perceptible physical barriers or habitat differentiation. Home ranges and burrow locations were derived from radio telemetry readings taken during the period of this study. The scale bar represents 100 m.
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