Predicting Preferred Prey of Sumatran Tigers Panthera Tigris Sumatrae Via Spatio-Temporal Overlap
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Predicting preferred prey of Sumatran tigers Panthera tigris sumatrae via spatio-temporal overlap M AXIMILIAN L. ALLEN,MARSYA C. SIBARANI and M IHA K ROFEL Abstract Encounter rates of carnivores with prey are Introduction dependent on spatial and temporal overlap, and are often highest with their preferred prey. The Critically Endangered nterspecific interactions are important aspects of com- Sumatran tiger Panthera tigris sumatrae is dependent on Imunity ecology, affecting the functional ecology of eco- prey populations, but little is known about its prey prefer- systems and dictating the ecological niches inhabited by ences. We collected camera-trap data for years (–) species (Begon et al., ). Such interactions can be diffi- in Bukit Barisan Selatan National Park, Sumatra, to investi- cult to assess, however, particularly for cryptic species such gate spatial and temporal overlap of tigers with potential as wild carnivores (Allen et al., ; Saggiomo et al., ). – prey species. We also developed a novel method to predict Carnivore prey encounter rates are dependent on spatial predator–prey encounter rates and potential prey preferences and temporal overlap, and high encounter rates are often in- from camera-trap data. We documented at least individual dicative of prey preference (Holling, ; Fortin et al., ). tigers, with an overall detection rate of . detections/ Data on spatio-temporal overlap of carnivores with poten- trap nights. Tigers exhibited a diurnal activity pattern and tial prey species may thus facilitate inference of prey prefer- had highest temporal overlap with wild boar Sus scrofa and ences and patterns of interspecific interactions, providing pig-tailed macaques Macaca nemestrina, but highest spatial insights into ecosystem functions that can inform effective overlap with wild boar and sambar deer Rusa unicolor.We conservation. Camera trapping is a non-invasive method created a spatial and temporal composite score and three that is increasingly being used to monitor wildlife and additional composite scores with adjustments for the spatial provides data on species richness, behaviour, and spatio- overlap and preferred prey mass. Wild boars ranked highest temporal activity (Swanson et al., ; Rich et al., ; for all composite scores, followed by sambar deer, and both Allen et al., ). are known as preferred tiger prey in other areas. Spatial and The tiger Panthera tigris is categorized as Endangered temporal overlaps are often considered as separate indices, throughout its range, with four subspecies probably extinct but a composite score may facilitate better predictions of en- in the wild (Seidensticker, ; Goodrich et al., ). counter rates and potential prey preferences. Our findings sug- The Sumatran tiger Panthera tigris sumatrae is Critically gest that prey management efforts in this area should focus Endangered (Linkie et al., ), as are many other species ’ on wild boar and sambar deer, to ensure a robust prey base for on the Indonesian island of Sumatra (O Brien & Kinnaird, this Critically Endangered tiger population. ; Pusparini et al., ). Prey abundance can have strong effects on the abundance and population density of tigers Keywords Activity patterns, composite score, Panthera (Karanth et al., ; Barber-Meyer et al., ), and tiger tigris, prey preference, spatial overlap, Sumatra, temporal declines have been linked to declines of prey in Russia and overlap, tiger India (Miquelle et al., ; Ramakrishnan et al., ). The Supplementary material for this article is available at prey preferences of tigers are unknown in many areas, but doi.org/./S such knowledge is important to inform conservation planning and ensure sufficient prey is available in areas critical to tiger conservation. Information about the Sumatran tiger’s diet is limited (e.g. O’Brien et al., ; Linkie & Ridout, ), and data on spatial and temporal activity patterns and overlap between tigers and potential prey could improve our under- standing of the subspecies’ prey preferences. Bukit Barisan Selatan National Park is one of the largest MAXIMILIAN L. ALLEN (Corresponding author, orcid.org/0000-0001-8976- protected areas on the island of Sumatra, and is critical 889X) Illinois Natural History Survey, University of Illinois, 1816S. Oak for the conservation of the Sumatran tiger and other Street, Champaign, Illinois 61820, USA. E-mail [email protected] species of conservation concern, including the Critically MARSYA C. SIBARANI Wildlife Conservation Society—Indonesia Program, Bogor, West Java, Indonesia Endangered Sumatran rhinoceros Dicerorhinus sumatren- sis and Sumatran elephant Elephas maximus sumatranus MIHA KROFEL ( orcid.org/0000-0002-2010-5219) Department of Forestry, ’ Biotechnical Faculty, University of Ljubljana, Ljubljana, Slovenia (O Brien & Kinnaird, ; Pusparini et al., ). The Park Received January . Revision requested April . provides relatively abundant tiger habitat, but threat levels Accepted May . are moderate to high because of inadequate conservation Oryx, Page 1 of 7 © 2020 Fauna & Flora International doi:10.1017/S0030605319000577 Downloaded from https://www.cambridge.org/core. University of Illinois at Urbana - Champaign Library, on 11 Mar 2020 at 13:47:11, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1017/S0030605319000577 2 M. L. Allen et al. measures (Sanderson et al., ). Given the Park’simportance for tiger conservation, it is important to understand the spe- cies’ ecology in this area. Previous studies of activity patterns of Sumatran tigers in the Park produced conflicting results; O’Brien et al. () reported tigers had a diurnal activity pattern, whereas Pusparini et al. () reported a crepuscular activity pattern with highest activity levels near dawn. The tigers’ prey preferences and prey abundance in the area are also unknown. To inform conservation efforts, we investigated tiger spatio-temporal overlap with potential prey species, using years of camera-trap data from an area of the Park with little human activity. Our objectives were to () document the minimum number of individual tigers in the area, () deter- mine the temporal and spatial overlap of tigers with six po- tential prey species, and () create a composite score from the indices of temporal and spatial overlap as a novel method to predict predator–prey encounter rates and determine poten- tial prey preference. In our analyses we included all potential tiger prey species present in the study area, based on a review of tiger dietary studies (Hayward et al., ). In line with known prey preferences of tigers across their range, we ex- pected sambar deer Rusa unicolor and wild boar Sus scrofa to have the highest composite spatio-temporal score. FIG. 1 The study site with camera-trap locations of both arrays within Bukit Barisan Selatan National Park on the island of Sumatra, Indonesia. Study area Our study site is in Bukit Barisan Selatan National Park, in designed our survey to monitor multiple species effectively the South Barisan Range ecosystem on the Indonesian is- (Rich et al., ). We set two arrays of camera traps, land of Sumatra (Fig. ). The Park is the third largest pro- using the Network’s protocols (TEAM Network, ), in tected area (, km ) on Sumatra (O’Brien & Kinnaird, sites chosen for accessibility for long-term repeated surveys, ), spanning two provinces: Lampung and Bengkulu. all in lowland forests at – m altitude. We placed camera Topography ranges from coastal plains and lowland rain- traps in each array at a density of per km (Fig. ), and forest at sea level in the southern peninsula of the Park the arrays covered a total of . km . We deployed the to mountains up to , m in the central and northern camera-trap arrays in the dry season (April–July) of each parts (Pusparini et al., ). The Park contains montane, year during –, with array in operation during lowland tropical, coastal and mangrove forests. Annual April–May and array during June–July, with the aim to rainfall is ,–, mm, most of which falls in the mon- complete at least sampling days for each camera trap. soon season (November–May), and annual temperatures We positioned camera traps near animal trails and/or are – °C (O’Brien et al., ). The Park contains a high places used regularly by wildlife, to maximize detections. diversity of wildlife, with tigers and other species listed We placed camera traps – cm off the ground, with no in the CITES Appendices and categorized as Endangered refractory period between images. or Critically Endangered on the IUCN Red List. Statistical analyses Methods To avoid pseudo-replication, we considered consecutive Camera trapping photo captures of the same species as independent events only if they occurred after an interval of . min We set camera traps in the Park as part of the Tropical (Rovero & Zimmermann, ). We calculated the number Ecology and Assessment Monitoring Network, which col- of independent captures for each species, but combined lects long-term biodiversity data in tropical environments both mouse deer species (greater mouse deer Tragulus globally to guide conservation actions. Our goal was to napu and lesser mouse deer Tragulus kanchil) in one cat- monitor the terrestrial vertebrate community, and we egory because they share similar characteristics as potential Oryx, Page 2 of 7 © 2020 Fauna & Flora International doi:10.1017/S0030605319000577 Downloaded from https://www.cambridge.org/core. University of Illinois at Urbana - Champaign