Altered food habits? Understanding the feeding preference of free-ranging Grey langurs within an urban settlement

Urbanization affects concurrent human-animal interactions as a result of altered resource availability and land use pattern, which leads to considerable ecological consequences. While some animals have lost their habitat due to urban encroachment, few of them managed to survive within the urban ecosystem by altering their natural behavioural patterns. The feeding repertoire of folivorous colobines, such as grey langur, largely consists of plant parts. However, these free-ranging langurs tend to be attuned to the processed high-calorie food sources to attain maximum benefits within the concrete jungle having insignificant greenery. Therefore, besides understanding their population dynamics, the effective management of these urbanized, free-ranging, non-human primate populations also depends on their altered feeding habits. Here, we have used a field-based experimental setup that allows grey langurs to choose between processed and unprocessed food options, being independent of any inter-specific conflicts over resources due to food scarcity. The multinomial logit model reveals the choice-based decision-making of these free-ranging grey langurs in an urban settlement of West Bengal, India, where they have not only learned to recognize the human-provisioned processed food items as an alternative food source but also shown a keen interest in it. However, such a mismatch between the generalized feeding behaviour of folivorous colobines and their specialized gut physiology reminds us of Liem’s paradox and demands considerable scientific attention. While urbanization imposes tremendous survival challenges to these animals, it also opens up for various alternative options for surviving in close proximity to humans which is reflected in this study, and could guide us for the establishment of a sustainable urban ecosystem in the future.城市化进程通过改变资源可获得性与土地利用格局，影响了人类与野生动物的共生互动关系，并由此引发诸多显著的生态后果。部分动物因城市扩张侵占栖息地而流离失所，但仅有少数物种能够通过调整自身自然行为模式，在城市生态系统中存活下来。食叶疣猴亚科动物（folivorous colobines）的取食谱以植物组织为主，例如灰叶猴（grey langur）。然而，这些自由活动的灰叶猴却逐渐适应了加工过的高能量食物，以在绿植稀少的“混凝土丛林”中获取最大的能量收益。因此，除了掌握它们的种群动态之外，对这些城市化、自由活动的非人灵长类种群进行有效管理，也有赖于了解它们已发生改变的取食习性。本研究采用了基于野外的实验装置，让灰叶猴可以在加工食品与未加工食品之间进行选择，且该装置不受食物短缺引发的种间资源竞争干扰。多项逻辑斯蒂回归模型（multinomial logit model）的分析结果显示，在印度西孟加拉邦的一处城镇栖息地中，这些自由活动的灰叶猴会基于选择做出决策——它们不仅已学会将人类投喂的加工食品视为替代食物来源，还对这类食物表现出强烈的兴趣。然而，食叶疣猴亚科动物泛化的取食行为与其特化的肠道生理之间的这种不匹配，让我们联想到利姆悖论（Liem’s paradox），该现象亟需学界给予充分的科学关注。尽管城市化给这些动物带来了极大的生存挑战，但也为它们提供了多种与人类近距离共存的生存选择——本研究即印证了这一点，该研究成果也可为未来可持续城市生态系统的构建提供参考。