Faculty of Environmental Sciences Institute of Forest Botany and Forest Zoology Chair of Forest Zoology How to manage an uncommon alien rodent on a protected island? A study of the population structure, dynamics, and management of the rock cavy in Fernando de Noronha, Brazil Dissertation for obtaining the academic degree Doctor rerum naturalium (Dr. rer. nat.) presented by Tatiane Micheletti Ribeiro Silva, M.Sc. born on September 5th, 1983 in São Paulo, Brazil Supervisors: Prof. Dr. rer. nat. Mechthild Roth Prof. Dr. rer. nat. Uta Berger Prof. Dr. James Russell Day of Defense: 09th October 2017 Declaration of conformity I hereby confirm that this copy is identical with the original dissertation entitled: How to manage an uncommon alien rodent on a protected island? A study of the population structure, dynamics, and management of the rock cavy in Fernando de Noronha, Brazil Tharandt, 8th June 2017 __________________________________________ MSc. Tatiane Micheletti Ribeiro Silva To the loves of my life. “Look deep into nature, and then you will understand everything better.” Albert Einstein II Acknowledgement I would like to thank CPNq for funding my PhD in Germany (Process No. 246171/2012- 0), as well as Rufford Foundation, PVE/CAPES, the Graduate Academy of TU Dresden and the Friends of TU Dresden for the funding of field trips for data collection and presentations related to the project. I would like to sincerely thank my supervisors Prof. Dr. Mechthild Roth and Prof. Dr. Uta Berger for all the excellent inputs, long-lasting patience in the process of improving this monograph, and their invaluable support during the last years. In the same way, I deeply thank Prof. Dr. James Russell, Prof. Dr. Ricardo Dias and Dr. Paulo Mangini for all guidance and company in the field and during the elaboration of this thesis. We not only shared good laughs, but I am positive I have improved my scientific abilities in the last years because of you. My deepest gratitude to my dear Renata C. F. Santos and my reptile friends Vinicius Gasparotto and Carlos Abrahão not only for the help in the field, but mainly for the true friendship in the last years. The present work would also not have been possible without the vital support of the team of the National Marine Park of Fernando de Noronha, particularly M.Sc. Thayná J. Mello and M.Sc. Eduardo C. de Macedo. They are not only great scientists, but are an example that excellency in the management of Conservation Units can be achieved in Brazil. The same I can say about my colleagues from TRÍADE, especially Prof. Dr. Jean Carlos Ramos Silva, the coordinator of the project that encompasses the current research. The present project would also not have been possible without the support with accommodation in the island provided by the Brazilian Navy (CPPE and 3º Distrito Naval), as well by PARNAMAR/ICMBio. I would also like to acknowledge all the support the local community and administration of Fernando de Noronha gave to the whole project. Fundamental changes for protecting nature are not made without the support of the local inhabitants. My deepest appreciation to all my beloved friends from Germany and Brazil for your moral support, thesis reviews, abstract translation, beers, pizzas, and laughs. I would not have made it without you. Even far away, I would also like to thank my family, from the bottom of my heart, for all the support and incentives in the last years. You made me understand that it is necessary much more than physical distance to keep a family apart. At last, I wanted to thank the loves of my life François Jost and Sophie Nicole for their unmeasurable patience, love, and support, especially in the last months. You kept me sane and made me feel loved. I will never be able to express how much you two mean to me. III Abstract It appears to be unanimous that alien species in island environments tend to cause considerably more negative than positive impacts. To assess the potential level of threat aliens may pose to the native environment, understanding a species’ population structure and dynamics is of ultimate importance. Assessing both impacts and consequences of management interventions to alien species is likewise only possible through the comprehension of its population structure and dynamics. This can be achieved by estimating the number of individuals in the study site, as well as other population parameters through time, applying population models such as capture-recapture to the collected datasets. Nonetheless, alien species that have low capture rates, such as small mammals, might present a considerable obstacle for conservation, as available capture- recapture models need a relatively large dataset to precisely and accurately estimate population parameters. To improve accuracy and precision of estimates that use sparse datasets, the present study developed an integrated concurrent marking-observation capture-recapture model (C-MOM). The model proposed here, contrary to the commonly available mark-recapture and mark-resight models, allows for two different datasets (i.e. a capture-recapture and a population count) to be integrated, as well as for marking and observation (recapture) data to be collected simultaneously. While few models can integrate different datasets, no model is known to allow for concomitant capture-mark- observation activities. To assess the performance of the C-MOM when estimating population parameters for sparse datasets, a virtual ecology study was carried out. The population dynamics of a small rodent, the rock cavy (Kerodon rupestris), as well as capture-recapture and population count datasets, were simulated under different scenarios. The sampled datasets were then analyzed by the C-MOM, and by two other established statistical models: a classical mark recapture (CMR) (based on the Jolly-Seber model), and a zero-truncated Poisson log-normal mixed effects (ZPNE), the only integrated mark-resight model that allows for recapture sampling with replacement. Estimates of population parameters provided by the three models were then compared in terms of bias, precision and accuracy. C-MOM and ZPNE models were afterwards applied to real data collected on a rock cavy colony in the island of Fernando de Noronha. The estimated parameters were used to extrapolate the number of individuals in the rock IV cavy colony to the whole population in the island. Subsequently, these results were used to develop a risk assessment for the species by modelling historical and management scenarios, simulating both the establishment of the species in the island, and the consequences of different management interventions applied to it. The virtual ecology study showed that, in comparison to the CMR and the ZPNE, the C-MOM presented improved accuracy without overestimating the precision of population parameter’s estimates. The last also presented reduced amplitude of the calculated credible interval at 95% when applied to real data in comparison to the ZPNE. While the extrapolation of C-MOM estimates suggests that the rock cavy population in Fernando de Noronha is 6,652 ± 1,587, ZPNE estimates are of 5,854 ± 3,269 individuals. In the risk assessment, historical simulation models demonstrated that even though different combinations of uncertainty in reproductive parameters of the rock cavy might be possible for the species, these did not interfere significantly in either establishment or spread of the rock cavy population in the island. Moreover, historical yearly mortality has most likely been under 30%. Regarding the species’ management simulations, the most effective management interventions to achieve population extinction were spaying and neutering of both sexes, although harvest effort presented the highest influence on this populations’ extirpation. Nonetheless, the relative influence of female and both sexes’ based interventions did not differ significantly regarding the frequency of extinction of stochastic replicates’. Moreover, none of the management interventions guaranteed the population extinction within the time span and harvest effort proposed for the management program. Neutering of both sexes was most inversely influential on time to extinction of this population, followed by removal of both sexes. Briefly, the C-MOM has proven to be a resourceful and precise model to estimate population parameters when low capture rates result in sparse datasets. Moreover, the rock cavy is well established in the island and likely at carrying capacity. In general, the risk assessment showed that the management interventions in the time span and harvest effort simulated in the present study were ineffective to extinguish the rock cavy population in Fernando de Noronha. Considering this, as well as the importance of investigating other vital factors to decide in favour of or contrary to the management of this species, it is recommended that both an impact assessment of the rock cavy and a cost-effectiveness analysis of the management interventions should be performed to complement the current study. V Zusammenfassung Es besteht weitgehend Konsens, dass gebietsfremde Arten Inselökosysteme tendenziell erheblich mehr negativ als positiv beeinflussen. Um das potenzielle Bedrohungsrisiko zu beurteilen, welches fremde Arten für einheimische Lebensräume darstellen, ist es von entscheidender Bedeutung, die Populationsstrukturen und –dynamiken dieser Arten zu verstehen. Die Bewertung von Auswirkungen und Managementmaßnahmen sowie deren Konsequenzen auf fremde Arten ist ebenfalls nur