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Yvette C. Ehlers Smith

Bio: Yvette C. Ehlers Smith is an academic researcher from University of KwaZulu-Natal. The author has contributed to research in topics: Biodiversity & Habitat. The author has an hindex of 12, co-authored 35 publications receiving 536 citations. Previous affiliations of Yvette C. Ehlers Smith include Ezemvelo KZN Wildlife & University of Exeter.

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TL;DR: It is suggested that the relatively constant availability of fruit in this habitat affords P. rubicunda regular access to a nutritionally superior food, and that reliance on fallback foods is therefore not required.
Abstract: Southeast Asia's lowland dipterocarp forests experience supra-annual "mast" fruiting and flowering events, in which the majority of trees reproduce simultaneously at irregular intervals, with extensive intervening periods of very low primate food availability. This scarcity of food results in a negative energy balance and a reliance on "fallback foods" in some primate species. By contrast, ombrogenous tropical peat-swamp forests are non-masting, and show lower variability of food availability. We sought to test the influence of fruit availability on primate diet and preference in peat-swamp habitats and assess whether it differs from masting forests. We collected behavioral-dependent feeding data on three adult females in a group of red langurs (Presbytis rubicunda: Colobinae) between January and December 2011 in Sabangau tropical peat-swamp forest, Central Kalimantan, Indonesia, as colobine monkeys are adaptated for folivory, and are therefore generally considered less reliant on temporally variable fruits than monogastric primates. We documented the highest level of granivory recorded to date in colobine monkeys: mean annual diet comprised 76.4% seeds and 7.3% other fruit parts; 7.7% young and 2.5% mature leaves; 2.8% flowers; 2.6% piths, and <1% on other minor food items. Fruit availability was fairly constant throughout the year and fruit parts were consumed at consistently higher levels than expected based on availability, confirming that fruit is preferred. Leaves and flowers were consumed consistently less than expected and thus are not preferred. There were no significant correlations between preferred food availability and consumption of potential fallback foods, suggesting that reliance on fallback foods did not occur in Sabangau during the study period. Furthermore, consumption of fruit was not significantly correlated with its availability. Our findings suggest that the relatively constant availability of fruit in this habitat affords P. rubicunda regular access to a nutritionally superior food, and that reliance on fallback foods is therefore not required.

76 citations

Journal ArticleDOI
TL;DR: The results suggest that colobine monkeys maintain larger than average ranges when high-quality food resources are available, and imply that protecting large, contiguous tracts of habitat is crucial in future conservation planning for Presbytis rubicunda.
Abstract: Knowledge of a species’ ranging patterns is vital for understanding its behavioral ecology and vulnerability to extinction. Given the abundance and even distribution of leaves in forested habitats, folivorous primates generally spend less time feeding; more time resting; have shorter day ranges; and require smaller home ranges than frugivorous primates. To test the influence of frugivory on ranging behavior, we established the activity budget and home-range size and use in a highly frugivorous population of the Borneo-endemic colobine, Presbytis rubicunda, within Sabangau tropical peat-swamp forest, Central Kalimantan, and examined relationships between fruit availability and ranging patterns. We collected 6848 GPS locations and 10,702 instantaneous focal behavioral scans on a single group between January and December 2011. The group had the largest home-range size recorded in genus Presbytis (kernel density estimates: mean = 108.3 ± SD 3.8 ha, N = 4 bandwidths). The annual activity budget comprised 48 ± SD 4.0% resting; 29.3 ± SD 3.9% feeding, 14.2 ± SD 2.5% traveling, and 0.4 ± SD 0.4% social behaviors. Mean monthly day-range length was the highest recorded for any folivorous primate (1645 ± SD 220.5 m/d). No significant relationships existed between ranging variables and fruit availability, and ranging behaviors did not vary significantly across seasons, potentially owing to low fluctuations in fruit availability. Our results suggest that colobine monkeys maintain larger than average ranges when high-quality food resources are available. Their extensive range requirements imply that protecting large, contiguous tracts of habitat is crucial in future conservation planning for Presbytis rubicunda.

67 citations

Journal ArticleDOI
TL;DR: In this article, the authors established the first population density estimates of the endemic red langur (Presbytis rubicunda) in Sabangau TPSF, the largest remaining contiguous lowland forest-block on Borneo.
Abstract: Because of the large-scale destruction of Borneo's rainforests on mineral soils, tropical peat-swamp forests (TPSFs) are increasingly essential for conserving remnant biodiversity, particularly in the lowlands where the majority of habitat conversion has occurred. Consequently, effective strategies for biodiversity conservation are required, which rely on accurate population density and distribution estimates as a baseline. We sought to establish the first population density estimates of the endemic red langur (Presbytis rubicunda) in Sabangau TPSF, the largest remaining contiguous lowland forest-block on Borneo. Using Distance sampling principles, we conducted line transect surveys in two of Sabangau's three principle habitat sub-classes and calculated group density at 2.52 groups km⁻² (95% CI 1.56-4.08) in the mixed-swamp forest sub-class. Based on an average recorded group size of 6.95 individuals, population density was 17.51 ind km⁻², the second highest density recorded in this species. The accessible area of the tall-interior forest, however, was too disturbed to yield density estimates representative of the entire sub-class, and P. rubicunda was absent from the low-pole forest, likely as a result of the low availability of the species' preferred foods. This absence in 30% of Sabangau's total area indicates the importance of in situ population surveys at the habitat-specific level for accurately informing conservation strategies. We highlight the conservation value of TPSFs for P. rubicunda given the high population density and large areas remaining, and recommend 1) quantifying the response of P. rubicunda to the logging and burning of its habitats; 2) surveying degraded TPSFs for viable populations, and 3) effectively delineating TPSF sub-class boundaries from remote imagery to facilitate population estimates across the wider peat landscape, given the stark contrast in densities found across the habitat sub-classes of Sabangau.

58 citations

Journal ArticleDOI
TL;DR: In this article, the authors used birds as a model in the Kruger to Canyons Biosphere, South Africa, to ask whether agriculture can add habitat components and bird species complementary to those already present, and whether habitat variables and bird functional traits can be used to identify bird species most likely to respond to habitat changes.
Abstract: Habitat conversion for agriculture is a major driver of global biodiversity loss, partly because of homogeneity within agri-ecosystems. Anthropogenic landscapes can also increase habitat heterogeneity and primary productivity, however, augmenting regional biodiversity, as species that exploit resources associated with human activities expand their ranges into novel ecological regions. We used birds as a model in the Kruger to Canyons Biosphere, South Africa, to ask whether agriculture can add habitat components and bird species complementary to those already present, and whether habitat variables and bird functional traits can be used to identify bird species most likely to respond to such habitat changes. We surveyed birds and measured habitat structure in 150 fixed-radius point counts each in natural habitat and mango orchards, and assessed relationships between habitat variables and bird functional traits. Despite mango orchards having greater vertical height structure because of tall (average 20 m) Casuarina windbreaks, they were missing the low-scrub (1–2 m woody cover) component of natural vegetation. We found that species whose life-history traits and ecological attributes were associated with structures missing from mango orchards were correspondingly absent from the orchards, which translated into the exclusion of 35 % of the bird species; bird assemblages within mango orchards were only a subset of those found in natural habitat. These findings suggest that knowledge of habitat structure, along with species’ functional traits can provide a predictive framework for effects that anthropogenic habitats may have on regional biodiversity, and allow management to reduce negative effects.

56 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated the influence of microhabitat complexity on mammal communities within forest and dense bush habitats, using occupancy modelling, and found vertical stratification gradients as observed in studies of tropical forest chronosequence, i.e. increased foliage density in lower habitat layers and decreased foliage density at higher habitat layers for dense bush, and vice versa for forest.
Abstract: The Indian Ocean Coastal Belt (IOCB) of South Africa is a natural forest-grassland mosaic, nested within an anthropogenic, mixed land-use matrix. Given the ongoing threat of agricultural expansion and urbanisation, we assessed the value of a buffer habitat (Coastal dense bush) for conserving forest species. We investigated the influence of microhabitat complexity on mammal communities within forest and dense bush habitats, using occupancy modelling. We found vertical stratification gradients as observed in studies of tropical forest chronosequence, i.e. increased foliage density in lower habitat layers and decreased foliage density in higher habitat layers for dense bush, and vice versa for forest. Structural composition suggests that dense bush is within a successional stage of secondary forest regeneration. Bushbuck (Tragelaphus scriptus) occupancy was higher in forest than dense bush, while the opposite was true for blue duiker (Philantomba monticola). Large-spotted genet (Genetta tigrina), Cape porcupine (Hystrix africaeaustralis) and marsh mongoose (Atilax paludinosus) occupancy remained constant between habitats. Grey duiker (Sylvicapra grimmia) occupancy varied greatly between dense bush (0.48 ± 0.01) and forest (0.16 ± 0.01). Dense bush appeared to maintain natural forest assemblages, and may play a crucial role in buffering IOCB forest patches, given their highly-restricted distribution. However, dense bush habitats have no protection status, but play a role in the conservation of forest plants and animals. Therefore, we advocate the inclusion of dense bush habitats in conservation networks focused on forests.

38 citations


Cited by
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TL;DR: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols used xiii 1.
Abstract: Preface to the Princeton Landmarks in Biology Edition vii Preface xi Symbols Used xiii 1. The Importance of Islands 3 2. Area and Number of Speicies 8 3. Further Explanations of the Area-Diversity Pattern 19 4. The Strategy of Colonization 68 5. Invasibility and the Variable Niche 94 6. Stepping Stones and Biotic Exchange 123 7. Evolutionary Changes Following Colonization 145 8. Prospect 181 Glossary 185 References 193 Index 201

14,171 citations

30 Apr 1984
TL;DR: A review of the literature on optimal foraging can be found in this article, with a focus on the theoretical developments and the data that permit tests of the predictions, and the authors conclude that the simple models so far formulated are supported by available data and that they are optimistic about the value both now and in the future.
Abstract: Beginning with Emlen (1966) and MacArthur and Pianka (1966) and extending through the last ten years, several authors have sought to predict the foraging behavior of animals by means of mathematical models. These models are very similar,in that they all assume that the fitness of a foraging animal is a function of the efficiency of foraging measured in terms of some "currency" (Schoener, 1971) -usually energy- and that natural selection has resulted in animals that forage so as to maximize this fitness. As a result of these similarities, the models have become known as "optimal foraging models"; and the theory that embodies them, "optimal foraging theory." The situations to which optimal foraging theory has been applied, with the exception of a few recent studies, can be divided into the following four categories: (1) choice by an animal of which food types to eat (i.e., optimal diet); (2) choice of which patch type to feed in (i.e., optimal patch choice); (3) optimal allocation of time to different patches; and (4) optimal patterns and speed of movements. In this review we discuss each of these categories separately, dealing with both the theoretical developments and the data that permit tests of the predictions. The review is selective in the sense that we emphasize studies that either develop testable predictions or that attempt to test predictions in a precise quantitative manner. We also discuss what we see to be some of the future developments in the area of optimal foraging theory and how this theory can be related to other areas of biology. Our general conclusion is that the simple models so far formulated are supported are supported reasonably well by available data and that we are optimistic about the value both now and in the future of optimal foraging theory. We argue, however, that these simple models will requre much modification, espicially to deal with situations that either cannot easily be put into one or another of the above four categories or entail currencies more complicated that just energy.

2,709 citations

Journal ArticleDOI

279 citations