Evaluating environmental, demographic and genetic effects on population‐level survival in an island endemic

Abstract

The population dynamics of island species are considered particularly sensitive to variation in environmental, demographic and/or genetic processes. However, few studies have attempted to evaluate the relative importance of these processes for key vital rates in island endemics. We integrated the results of long‐term capture–mark–recapture analysis, prey surveys, habitat quality assessments and molecular analysis to determine the causes of variation in the survival rates of Komodo dragons Varanus komodoensis at 10 sites on four islands in Komodo National Park, Indonesia. Using open population capture–mark–recapture methods, we ranked competing models that considered environmental, ecological, genetic and demographic effects on site‐specific Komodo dragon survival rates. Site‐specific survival rates ranged from 0.49 (95% CI: 0.33–0.68) to 0.92 (0.79–0.97) in the 10 study sites. The three highest‐ranked models (i.e. ΔQAICc < 2) explained ∼70% of variation in Komodo dragon survival rates and identified interactions between inbreeding coefficients, prey biomass density and habitat quality as important explanatory variables. There was evidence of additive effects from ecological and genetic (e.g. inbreeding) processes affecting Komodo dragon survival rates. Our results indicate that maintaining high ungulate prey biomass and habitat quality would enhance the persistence of Komodo dragon populations. Assisted gene flow may also increase the genetic and demographic viability of the smaller Komodo dragon populations.

Isolating Chromosomes of the Komodo Dragon: New Tools for Comparative Mapping and Sequence Assembly

“…Considered "vulnerable" by the International Union for Conservation of Nature [IUCN, 2012], V. komodoensis is a keystone and umbrella species for the Monsoon forest ecosystem [Mills et al, 1993;Roberge and Angelstam, 2004] and plays an important role in the Lesser Sunda ecotourism development. A number of studies have been conducted on the population ecology, genetics, physiology, microbiology, management, and conservation of both captive and wild populations [e.g., Auffenberg, 1981;Ciofi et al, 1999;Montgomery et al, 2002;Murphy et al, 2002;Ciofi and de Boer, 2004;Watts et al, 2006;Ciofi et al, 2007;Jessop et al, 2007;Fry et al, 2009;Laver et al, 2012;Purwandana et al, 2014Purwandana et al, , 2015Ariefiandy et al, 2015;Bishop et al, 2017]. However, information on cytogenetics and genomics of this species is limited.…”

Identifying island safe havens to prevent the extinction of the World’s largest lizard from global warming

“…Komodo dragons have been the focus of intensive long‐term and large‐scale population monitoring efforts, generating temporal and spatial occupancy and demographic data (Ariefiandy, Purwandana, Natali, et al, 2015; Ciofi et al., 2007; Purwandana et al., 2014, 2015; Sastrawan & Ciofi, 2002). We used these data to parameterize our NPM and make predictions of climate change impacts on the future abundance and distribution of Komodo dragons.…”

“…Higher altitudes (>600 m elevation) and moist forest habitats constrain the distribution of the Komodo dragon, causing them to rarely be found more than 5–6 km from the shoreline (Auffenberg, 1981). Conversely, flatter and drier areas are commonly characterized by lowland savannah woodland and lowland deciduous forests (<300 m elevation), the latter being the most preferred habitat for Komodo dragons (Auffenberg, 1981) and their prey (Purwandana et al., 2015).…”

“…They occupy a highly restricted range distribution (Ciofi & De Boer, 2004) and are considered “Vulnerable” by the International Union for Conservation of Nature (IUCN, 2017). However, the last IUCN Red List assessment for the species was done over 20 years ago (World Conservation Monitoring Centre, 1996), and since this time, there has been considerable research on trends in Komodo dragon population abundance and range area (Imansyah, Jessop, Ciofi, & Akbar, 2008; Jessop et al., 2007, 2018; Purwandana et al., 2014, 2015). Therefore, a reassessment of the present‐day threat status of Komodo dragons is overdue.…”

Exploring mechanisms and origins of reduced dispersal in island Komodo dragons

“…kg prey/km 2 ) of Rusa deer (Rusa timorensis), wild pigs (Sus scrofa), and water buffalo (Bubalus bubalis) could influence the dispersal and survival of Komodo dragons. We used faecal counts, corrected based on their relationship with animal density and biomass, to estimate site-specific ungulate biomass [35,36]. (2) Komodo dragon inbreeding coefficients and relatedness.…”