Maintaining connectivity for tropical rainforest mammals in agricultural landscapes

Yaap, Elizabeth Allison (2018) Maintaining connectivity for tropical rainforest mammals in agricultural landscapes. PhD thesis, James Cook University.

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Across the tropics, agricultural activities and tree plantations are rapidly expanding to meet growing human needs for food, wood and fiber. Such developments are reducing the extent of forests and severing remaining forest blocks, thereby reducing and fragmenting wildlife habitat. Large mammals are particularly vulnerable to such habitat loss and fragmentation because of their large area needs and high susceptibility to poaching and other human pressures. My research focuses on maintaining connectivity for large mammals in fragmented landscapes within two of the world's recognized biodiversity hotspots, the rainforests of central Sumatra, Indonesia and the Osa Peninsula of Costa Rica.

I used camera traps and rapid-survey techniques to investigate the local distribution of larger (>1 kg) mammals, aiming to improve survey methods and devise wildlife-management recommendations in agricultural landscapes. My general objectives were to:

1. Survey the extent and type of scientific research that has been conducted to date on "biological corridors" (remnant or linear vegetation that could provide avenues for wildlife movements or habitat for animal occupancy) in tropical forests; and identify findings of particular relevance for the use of such corridors by larger mammals in the tropics.

2. Assess the efficacy of various rapid-assessment methods used to survey mammals in agricultural and timber-plantation landscapes, by comparing (a) automatic camera traps with without baiting and with (b) data collected from community interviews and from expert opinion.

3. Test the influence of landscape and site variables that could affect the use of biological corridors by individual mammal species, using camera trap data and occupancy models. The influence of factors such as corridor width, length, habitat type, surrounding matrix, and distance to core habitat was tested individually in two broad types of potential biological corridors: (a) linear riparian-forest remnants within an industrial wood-pulp (Acacia mangium) planation in Sumatra, and (b) a mixed-use landscape with a mosaic of natural and agricultural lands between three protected areas on the Osa Peninsula.

My literature review indicates that landscape-scale corridors are a popular conservation strategy in tropical countries, but much of scientific literature on the effectiveness of tropical forest corridors has focused on relatively small spatial scales. The limited scale of these studies precludes an effective analysis of broader ecological processes across more extensive forest landscapes (on the order of >1,000 km² or more).

Studies of large mammals in tropical nations largely support the recommendations for corridor design from the more extensive body of literature on temperate-zone corridors. In broad terms, these studies suggest corridor use by large mammals may be enhanced by maximizing corridor connectivity, and minimizing human disturbances that degrade forest quality. Species tend to respond to corridors in species-specific manners, such that individual habitat predictors may influence some species positively while having little or even negative effects on other species. Anthropogenic disturbances such as hunting, logging, transport corridors, settlements, and mining near to corridors generally have a negative impact on corridor use by many species of high conservation significance. The proximity of large forest tracts nearby also has a positive and often strong effect on corridor usage. However, the literature I examined only rarely provided explicit tests of the importance of corridor width and length on corridor efficacy for wildlife occupancy or movements.

I compared the efficacy of three rapid assessment techniques – scent-baited camera traps, community interviews and expert interviews - for conducting rapid assessments of High Conservation Value (HCV) mammals. In particular, I contrasted the value of these rapid-survey approaches for producing an accurate regional-species inventory and effectively identifying the distribution of individual species across landscapes. I found that each method has certain advantages and appears to have varying efficacy for different species and geographic regions; no single method emerged as being consistently superior over the others. Rather, the three approaches appear to provide complementary information in different contexts, and all three have the potential to contribute to rapid HCV mammal assessments.

In Sumatra, I evaluated linear remnants of riparian forest in an industrial Acacia plantation, spanning a landscape of about 180 km² in area. I evaluated five corridor-design variables for large (>1 kg) mammals: corridor width, corridor length, distance of the sampling point from core forest habitat, direct connectivity with forest core habitat, and habitat type. The results suggest that linear riparian remnants of 100-200 m width can function as habitat and potential movement corridors for many large mammal species in Sumatra, at least for localized movements extending up to a few kilometers from intact forest. This study was the first to assess the habitat and landscape factors that influence the use of linear remnants by the Malay tapir (Tapirus indicus).

On a larger scale, in a 740 km² area of the Osa Biological Corridor in Costa Rica, I evaluated corridor design-variables for 16 large mammal species, focusing on species' habitat use and distance to nearby core habitats. I identified species-specific responses to six habitat types, demonstrating that the presence of forest had a strong positive effect on occupancy for almost all species. However, the linear distance to large blocks of forest (³500 ha) was a significant predictor for only a few species, emphasizing the conservation value of retaining smaller, fragmented forests across the corridor. The percentage land-cover of mangroves, grasslands and oil palm surrounding sample sites all had significant negative associations for many species across the large-mammal community. Using least-cost modeling to compare single-species and multi-species corridor models, I found that most corridors developed for single-species showed a strong overlap with the multi-species corridor created based on the average habitat preference of all species. Likewise, there was a minimal change in corridor cost for most species when comparing the multi-species corridor with those designed for single species. The findings from circuit-flow analyses, where I compared models of species movement routes using the same single and multi-species data used in the least-cost models, also supported this conclusion. Therefore, a single corridor designed for multiple species would potentially serve the majority of mammal species on the Osa Peninsula. The integrated approach of intensive landscape-scale sampling with camera traps, multi-species occupancy modeling and corridor modelling in this study is a cost-efficient approach and especially useful for defining regional corridors between protected areas at a scale ranging from a few hundred to a thousand square kilometres.

This study was the first to sample large mammal use of swamps dominated by the tree Raphia taedigera, which is a distinctive habitat type in Central America. My findings revealed that they provide potentially important habitat for maintaining wildlife connectivity across the Osa Biological Corridor.

Collectively, my findings further our understanding of biological corridor-design variables for large tropical mammals in Sumatra and Costa Rica. Rapid survey techniques show considerable promise for evaluating HCV habitats and for documenting species distributions, although each strategy I evaluated has some apparent advantages relative to the others. As detailed above, my results and habitat-management recommendations have a number of practical implications for enhancing large-mammal use in heterogeneous tropical landscapes. Human-dominated landscapes will continue to expand in the tropics, underscoring the importance of devising and implementing landscape-design principles that maximize the use of such lands by larger mammal species and other rare wildlife.

Item ID: 56038
Item Type: Thesis (PhD)
Keywords: acacia, corridor, Indonesia, mammal, plantation, tropical forest, camera trap, Costa Rica, mammmals, Raphia taedigera
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Copyright Information: Copyright © 2018 Elizabeth Allison Yaap
Additional Information:

Publications arising from this thesis are available from the Related URLs field. The publications are:

Chapter 4: Yaap, Betsy, Magrach, Ainhoa, Clements, Gopalasamy Reuben, McClure, Christopher J.W., Paoli, Gary D., and Laurance, William F. (2016) Large mammal use of linear remnant forests in an industrial pulpwood plantation in Sumatra, Indonesia. Tropical Conservation Science, 9 (4). pp. 1-13.

Chapter 6: Yaap, Betsy, Watson, Haley, and Laurance, William F. (2015) Mammal use of Raphia taedigera palm stands in Costa Rica's Osa Peninsula. Mammalia, 79 (3). pp. 357-362.

Date Deposited: 06 Nov 2018 01:39
FoR Codes: 05 ENVIRONMENTAL SCIENCES > 0502 Environmental Science and Management > 050202 Conservation and Biodiversity @ 100%
SEO Codes: 96 ENVIRONMENT > 9608 Flora, Fauna and Biodiversity > 960899 Flora, Fauna and Biodiversity of Environments not elsewhere classified @ 100%
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