Zoos and aquariums continue to play a growing role in conservation, serving as hubs for species knowledge, conserving biodiversity, and supplementing in situ populations via reintroduction. Crucial to these missions is the maintenance of viable ex situ animal populations, which is largely contingent upon cooperative management among institutions. To do this, recommendations are issued to all institutions regarding whether individual animals should be transferred and/or bred. Given small population sizes, active exchange of animals among institutions for breeding is necessary to maintain genetic and demographic health; however, previous research has indicated that not all recommended transfers are carried out (i.e., fulfilled). In this study, we examined institutional fulfillment of transfer recommendations using a network approach. We generated two sets of networks, one depicting the structure of transfer recommendations among institutions and the other characterizing transfer recommendations that were fulfilled. We then used exponential random graph models (ERGMs) to capture exchange of individual animals between institutions using elements of network structure and institutional attributes. We simulated 1000 networks and calculated predictive distances for network metrics to identify instances where transfer fulfillment significantly differed from the recommendation network.
Results/Conclusions
Using PMCTrack, a large online database storing breeding and transfer information about populations managed in accredited North American zoos and aquariums, we constructed networks using 1,706 transfer recommendations and 1,155 (67.7%) fulfilled transfers across 169 institutions from 2011-2019. Additionally, recommendations stemmed from 373 species survival plan (SSP) programs (i.e., species involved in captive breeding and cooperative population management). We found patterns in fulfillment were largely similar to the recommendation network. Overall, structure of both the recommendation and fulfilled transfer network were highly transitive, indicating that a subset of highly connected institutions were receiving the most recommendations and fulfilling the most transfers, for all taxonomic groups. In terms of institutional attributes, we found that budget and cooperative management tenure did not play a strong role in shaping transfer recommendation and fulfillment networks. Rather, institutions involved in older SSP programs and with more experienced SSP coordinators were more influential, where these attributes corresponded with a reduced likelihood of transfer fulfillment in sending institutions. Though transfer fulfillment remains at ~68%, our results suggest that overall network structure of fulfilled transfers maintains similar properties to the recommendation network. Seemingly, institution size and resources do not appear to drive transfer fulfillment but rather aspects of the programs they are involved and potential stochastic sources uncaptured in our analysis.