Sloth bear, Melursus ursinus
This paper is interesting from an ecological point of view, illustrating as it does the importance of maintaining a diverse habitat in order to maintain biodiversity, but it also neatly illustrates something which creationists either genuinely don't understand or about which they feign ignorance.
One of the most annoying questions creationists keep asking, as though they imagine it to be a killer question which destroys the idea of evolution, is, "If humans evolved out of monkeys, why are there still monkeys?" The slightly more educated ones will use 'apes' instead of 'monkeys', but the underlying ignorance is the same. This question can only seem even slightly intelligent to those who have no idea how speciation by population isolation occurs.
To anyone with more than a small inkling of the mechanisms of evolution, this question leaves them nonplussed, not because it's unanswerable, but because it's difficult to know where to begin with someone that ignorant, who is almost certainly that ignorant through choice or is even feigning it for effect. It's not as though the concept is hard to grasp or requires an in-depth understanding of some obscure aspect of biology, so it's hard to blame even a generally low level of cognitive ability. It most likely reflects a general unwillingness to think and an over-eagerness to conform to group norms and show group affiliation in a fundamentalist, creationist culture.
The paper's authors studied the genetic makeup of five isolated populations of sloth bears from five tiger reserves in central India by collecting hair and fecal samples:
Abstract
Sloth bears (Melursus ursinus) are endemic to the Indian subcontinent. As a result of continued habitat loss and degradation over the past century, sloth bear populations have been in steady decline and now exist only in isolated or fragmented habitat across the entire range. We investigated the genetic connectivity of the sloth bear meta-population in five tiger reserves in the Satpura-Maikal landscape of central India. We used noninvasively collected fecal and hair samples to obtain genotypic information using a panel of seven polymorphic loci. Out of 194 field collected samples, we identified 55 individuals in this meta-population. We found that this meta-population has moderate genetic variation, and is subdivided into two genetic clusters. Further, we identified five first-generation migrants and signatures of contemporary gene flow. We found evidence of sloth bears in the corridor between the Kanha and Pench Tiger Reserves, and our results suggest that habitat connectivity and corridors play an important role in maintaining gene flow in this meta-population. These corridors face several anthropogenic and infrastructure development threats that have the potential to sever ongoing gene flow, if policies to protect them are not put into action immediately.
Introduction
The importance of maintaining meta-populations of large carnivores in a landscape with habitat connectivity between source populations is an intuitive and logical concept supported by a large body of scientific evidence [1–3]. Small isolated populations that lack connectivity are at risk of suffering from low genetic variation, which combined with other factors, reduces the probability of overall persistence of populations and species [4,5]. Large carnivore conservation is a daunting task in human-dominated landscapes, particularly those not connected by functional linkages or a permeable matrix between natural areas [6]. Carnivores move over long distances, have high dispersal capabilities, and need corridors for movement, dispersal, and gene flow [2,7–9].
The sloth bear (Melursus ursinus) is a large wide-ranging carnivore species endemic to the Indian subcontinent (S1 Fig). It is a medium-sized ursid (adult males 75–140 kg; females 55–95 kg) and the only bear species with a suite of specialized adaptations for myrmecophagy (diet consisting of ants and termites) [10]. Sloth bears are omnivorous [11,12], feeding primarily on social insects (ants and termites) and a broad spectrum of plant material such as leaves, shoots, tubers, and seasonal fruits and flowers [13,14]. Their diet strongly follows the phenology of flowering and fruiting of plant species in their habitat. These resources are also collected and used by humans, which often lead to incidents of human-bear conflict [12,14,15].
Sloth bears are still widely distributed in a large part of their range in India, where patches of tropical forests still exist. The Western Ghats and Central India are major strongholds of their distribution in terms of population abundance and habitat availability [13]. In the recent country-wide census of large carnivores and their prey species [16], sloth bears were found to have the most widely recorded distribution of any large carnivore in the Central India and Eastern Ghats landscapes. Central India has the largest extent of habitat and largest population size of sloth bears in India, with ~180,000 km2 of sloth bear occupied forests [17]. However, their distribution has gradually decreased and become patchy due to habitat loss and fragmentation [13,18,19]. Within the current range of sloth bears, human activities are the predominant factors determining areas of occupancy [19]. Small isolated patches of forest and high human and road density are correlated with higher risk of sloth bear extirpation [13,20]. The continuous developmental and infrastructural growth (mines, roads, and dams) to support the growing economy of the subcontinent poses a great risk of further fragmentation and insularization of sloth bear occupied forests [19].
Bear policy documents such as the IUCN Bear Action Plan [21] and the National Bear Conservation and Welfare Action Plan (NBCWAP) of India [17] recognize that reducing the impacts of habitat fragmentation and human activities on sloth bear habitats is critical to sloth bear persistence, and also recommend research on the species at a landscape scale. The IUCN Bear Action Plan [21] emphasizes delineating discrete population units, rather than individual reserves, as the basis for their management and conservation strategies. These include establishing and managing additional protected areas and interconnecting and safeguarding corridors and buffer zones between protected areas. The NBCWAP [17] highlights the paucity of research and basic scientific information on sloth bears in India, and recommends genetic studies for recording presence/absence of bears in unsampled and non-protected areas.
Multiple studies have been conducted to understand population genetics of other bear species [22–28], but no information is available on population and landscape genetics of sloth bears. We undertook a project to fill existing gaps in information on sloth bear ecology, by describing the genetic variation in sloth bear populations in a large landscape consisting of four sloth bear populations in five tiger reserves interconnected by corridors in Central India. Given their generalist diet, patchy occupancy, and lack of information about their dispersal range and pattern, an ecological question of strong conservation relevance is how sloth bear allelic diversity is distributed within the landscape, and how existing corridors affect this allelic distribution. Our specific objectives in this study were to a) determine if sloth bears use corridors, b) describe the genetic variation and genetic structure of sloth bear populations in this landscape, and c) quantify gene flow among sloth bear populations in this landscape.
Study Landscape
We conducted our study in the Satpura-Maikal landscape in Central India (Fig 1). This landscape is characterized by the Satpura Range in the north and the Maikal Range in the east which form the catchments for the Narmada and the Tapti rivers and their tributaries. The landscape comprises five tiger reserves in two states: Kanha Tiger Reserve, Bori-Satpura Tiger Reserve (Satpura), and Pench Tiger Reserve are in the state of Madhya Pradesh (MP), while part of Pench Tiger Reserve and the Melghat Tiger Reserve are in the state of Maharashtra (Mh). Kanha and Pench are connected by a corridor and are located toward the eastern part of the landscape. Melghat and Satpura are connected by a corridor and lie to the west of the landscape. The connectivity between Kanha–Pench and Satpura–Melghat tiger reserves is largely contiguous forest cover, whereas the connectivity between Pench–Melghat and Pench–Satpura tiger reserves is fragmented. The intervening matrix in this landscape is composed of agricultural land and fragmented forest patches, interspersed with numerous small villages and towns.
Fig 1. Map of the study landscape with locations of all sloth bear fecal and hair samples collected shown in blue dots.
Tiger Reserve boundaries are indicated in orange.
https://doi.org/10.1371/journal.pone.0123384.g001Dutta T, Sharma S, Maldonado JE, Panwar HS, Seidensticker J (2015)
Genetic Variation, Structure, and Gene Flow in a Sloth Bear (Melursus ursinus) Meta-Population in the Satpura-Maikal Landscape of Central India.
PLoS ONE 10(5): e0123384. doi:10.1371/journal.pone.0123384
Copyright: © 2024 The authors.
Published by PLoS. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
What this illustrates is not only how an isolated population can begin to diversify genetically, but how, if there is limited population exchange, genes can flow between otherwise isolated populations. The important concept here is that genes flow, carried by individuals between populations. With enough gene flow, there is no possibility of genetic isolation being maintained long enough for the populations to diversify according to local conditions or genetic drift to the point where they can no longer interbreed.
Where there is only very occasional gene flow, or interbreeding is only possible in exceptional conditions, taxonomists may even consider them different species because they are functionally genetically distinct, or at least classify them as subspecies. The ultimate test of speciation is whether, if the populations ever come back into contact, they interbreed. If not, by definition, they are distinct species, yet nowhere in that process was there a single 'speciation event'.
Creationists need to invoke another fallacy and use double-think at this point, needing to pretend that somehow the evolutionary mechanism by which genetically isolated populations diverge to the point at which they are effectively different species is impossible, but the changes which lead to varieties and subspecies, and the fantastic rate of diversification required to give the range we see today in every species, from a founder population of two or three pairs a few thousand years ago, is entirely possible, whilst simultaneously claiming the entire process is rendered impossible by the Second Law of Thermodynamics [sic].
For example, from just the two or three pairs of 'bear kind', creationists must believe that not only the diversity seen in populations of sloth bears, brown pears, polar bears, grizzly bears, etc, etc, has evolved in a few thousand years, but so has the diversity seen between the different species, which are all really the same species even though they don't exchange genetic material and don't normally interbreed. Creationist need to use a lot of private definitions of terms like 'species', 'evolution', 'logic' and 'reason'.
The problem creationists have is that the real science of evolution doesn't fit well with the infantile parody they have been sold by creationist pseudo-scientist in order to give them reasons to doubt it and something idiotic to attack from a position of wilful, self-congratulatory, self-important ignorance.
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As I was reading your article, my mind was wandering off to those charts we see of evolution's progress. You know, the ones that start with an image of an early ape and then sequence through prehominids and finally a man. I wonder if some poor souls think they are witnessing the metamorphosis of an individual rather than the gradual change in the descendants of populations over long periods of time.
ReplyDeleteI think some of them do.
DeleteOthers seem to think evolution is a female of one species giving birth to a new species because of a random 'mutation'. Still others seem to imagine evolution is a species spontaneously self-assembling, fully formed, from some sort of soup. For reasons which aren't hard to work out, creationist pseudoscientists do nothing to disavow their victims of these misunderstandings and everything to encourage them.