Deni Purwandana

Life-history and spatial determinants of somatic growth dynamics in Komodo dragon populations

Somatic growth patterns represent a major component of organismal fitness and may vary among sexes and populations due to genetic and environmental processes leading to profound differences in life-history and demography. This study considered the ontogenic, sex-specific and spatial dynamics of somatic growth patterns in ten populations of the world’s largest lizard the Komodo dragon (Varanus komodoensis). The growth of 400 individual Komodo dragons was measured in a capture-mark-recapture study at ten sites on four islands in eastern Indonesia, from 2002 to 2010. Generalized Additive Mixed Models (GAMMs) and information-theoretic methods were used to examine how growth rates varied with size, age and sex, and across and within islands in relation to site-specific prey availability, lizard population density and inbreeding coefficients. Growth trajectories differed significantly with size and between sexes, indicating different energy allocation tactics and overall costs associated with reproduction. This leads to disparities in maximum body sizes and longevity. Spatial variation in growth was strongly supported by a curvilinear density-dependent growth model with highest growth rates occurring at intermediate population densities. Sex-specific trade-offs in growth underpin key differences in Komodo dragon life-history including evidence for high costs of reproduction in females. Further, inverse density-dependent growth may have profound effects on individual and population level processes that influence the demography of this species.

Can Camera Traps Monitor Komodo Dragons a Large Ectothermic Predator

Camera trapping has greatly enhanced population monitoring of often cryptic and low abundance apex carnivores. Effectiveness of passive infrared camera trapping, and ultimately population monitoring, relies on temperature mediated differences between the animal and its ambient environment to ensure good camera detection. In ectothermic predators such as large varanid lizards, this criterion is presumed less certain. Here we evaluated the effectiveness of camera trapping to potentially monitor the population status of the Komodo dragon (Varanus komodoensis), an apex predator, using site occupancy approaches. We compared site-specific estimates of site occupancy and detection derived using camera traps and cage traps at 181 trapping locations established across six sites on four islands within Komodo National Park, Eastern Indonesia. Detection and site occupancy at each site were estimated using eight competing models that considered site-specific variation in occupancy (ψ)and varied detection probabilities (p) according to detection method, site and survey number using a single season site occupancy modelling approach. The most parsimonious model [ψ (site), p (site*survey); ω = 0.74] suggested that site occupancy estimates differed among sites. Detection probability varied as an interaction between site and survey number. Our results indicate that overall camera traps produced similar estimates of detection and site occupancy to cage traps, irrespective of being paired, or unpaired, with cage traps. Whilst one site showed some evidence detection was affected by trapping method detection was too low to produce an accurate occupancy estimate. Overall, as camera trapping is logistically more feasible it may provide, with further validation, an alternative method for evaluating long-term site occupancy patterns in Komodo dragons, and potentially other large reptiles, aiding conservation of this species.

Monitoring the ungulate prey of the Komodo dragon Varanus komodoensis: distance sampling or faecal counts?

Monitoring the abundances of prey is important for informing the management of threatened and endangered predators. We evaluated the usefulness of faecal counts and distance sampling for monitoring the abundances of rusa deer Rusa timorensis, feral pig Sus scrofa and water buffalo Bubalus bubalis, the three key prey of the Komodo dragon Varanus komodoensis, at 11 sites on five islands in and around Komodo National Park, eastern Indonesia. We used species-specific global detection functions and cluster sizes (i.e. multiple covariates distance sampling) to estimate densities of rusa deer and feral pig, but there were too few observations to estimate densities of water buffalo. Rusa deer densities varied from from 2.5 to 165.5 deer/km2 with coefficients of variation (CVs) of 15-105%. Feral pig densities varied from 0.0 to 25.2 pigs/km2 with CVs of 25-106%. There was a positive relationship between estimated faecal densities and estimated population densities for both rusa deer and feral pig: the form of the relationship was non-linear for rusa deer, but there was similar support for linear and non-linear relationships for feral pig. We found that faecal counts were more useful when ungulate densities were too low to estimate densities with distance sampling. Faecal count methods were also easier for field staff to conduct than distance sampling. Because spatial and temporal variation in ungulate density is likely to influence the population dynamics of the Komodo dragon, we recommend that annual monitoring of ungulates in and around Komodo National Park be undertaken using distance sampling and faecal counts. The relationships reported here will also be useful for managers establishing monitoring programmes for feral pig, rusa deer and water buffalo elsewhere in their native and exotic ranges.

Temporal and spatial dynamics of insular Rusa deer and wild pig populations in Komodo National Park

The roles of density-dependent and density-independent factors in the dynamics of tropical large herbivore populations are poorly understood. Understanding these dynamics is particularly important if the herbivore is prey for an apex predator of conservation concern because a decline in the prey could cause the predator to decline. We tested hypotheses about the roles of density-dependent and density-independent factors in the dynamics of 2 tropical ungulates, Rusa deer (Rusa timorensis) and wild pigs (Sus scrofa), in Komodo National Park, eastern Indonesia. We counted the dung of Rusa deer and wild pigs (a validated index of abundance for these 2 species) along permanently marked transects at 10 sites over 4 islands annually during 2003–2014 to estimate ungulate abundance. Ungulates were much more abundant on the 2 larger islands compared with the 2 smaller islands, with wild pig dung completely absent from the latter. During our 12-year study, Rusa deer abundance declined slightly on Nusa Kode and Rinca islands, did not change on Komodo Island, and increased on Gili Motang Island. There was a decline in abundance of wild pigs on Komodo Island and an increase on Rinca Island. Annual variation in population growth rate was strongly density-dependent and island-specific for both species, with annual rainfall and vegetation composition being relatively unimportant. Population growth rates of Rusa deer exhibited spatial synchrony, with synchrony declining with increasing intersite distance. Our findings confirm the importance of density dependence in the dynamics of tropical large herbivore populations. However, the strength of density dependence varied between species and spatially. Declines of Rusa deer and wild pigs on the larger 2 islands, which are strongholds of the Komodo dragon, are cause for concern. Continued monitoring of ungulate populations is critical for the conservation of Komodo dragon populations in Komodo National Park.

Assessment of environmental and host dependent factors correlated with tick abundance on Komodo dragons

In this study we assessed interactions among Komodo dragon Varanus komodoensis populations, individual Komodo dragons and two tick parasites Amblyomma robinsoni and Aponomma komodoense to assess variation in host-parasite aggregations. Prevalence of ticks was uniformly high (> 98%) but median tick abundance varied 3.52 fold among 9 host lizard populations. There was no evidence to suggest that average tick abundances were correlated with genetic similarities (Rm = 0.133, P = 0.446) or geographic proximities (Rm = 0.175 P=0.303) among host populations. Temporal concordance in tick abundance was measured for host populations between two different years but not for the individual hosts within these populations. General linearized modelling indicated that ≈ 23% of host variation in tick abundance was positively correlated to a multivariate function incorporating lizard body size, body condition, their interactions, and habitat differences. The covariates of host population density and inbreeding coefficients,...