Investigating the Impact of Habitat Disturbance and the Role of Functional Traits in a Tropical Butterfly Assemblage

Abstract

Tropical habitats face a diverse range of anthropogenic threats. Two common and important threats to tropical biodiversity are invasive species and roads. Invasive plants are proposed to be a major threat to biodiversity worldwide, yet not much is known about their impacts on higher trophic levels, such as insects. Roads and other linear intrusions, such as power lines and railway tracks, are another common aspect of human disturbance in natural landscapes, including tropical forests, and are often linked to the spread of invasive plants. I studied impacts of these two important proximate drivers of habitat disturbance, namely invasive plant species and roads, on habitat use by butterflies in a tropical moist deciduous forest in Western Ghats of India. Invasive plants and roads are expected to modify micro-habitat structure, resources and other aspects of ecology of butterflies and thereby influence how they use space (i.e., micro-habitats within the larger habitat). Because systematic ecological information on tropical butterflies is comparatively limited, I adopted a multi-species approach. I examined space use responses of butterflies to a gradient of lantana cover in the forest and to a road passing through forest. The abundance of different species of butterflies in different micro-habitats was taken as a measure of habitat use. Data was collected over two seasons and at two spatial scales. The two habitat disturbances were found to influence local habitat use by butterflies. But interestingly, species appeared to respond differently, with some showing positive, others negative and some no clear association with road verge or lantana gradient. I then examined whether this variation in response could be understood in terms of species-specific functional traits. Correlating the responses of species to a habitat disturbance with functional traits may provide a way of arriving at general patterns and increase the ability of studies to predict responses. Species with similar trait values are expected to respond similarly to a habitat change driver. I measured morphological traits in 254 butterfly species from India and classified them according to their habitat preferences (based on expert opinion). I first examined relationships between morphological traits, habitat preferences and evolutionary relatedness. I then examined patterns of correlation between these traits and responses to the two habitat disturbances and found that certain traits can help predict responses. Overall, my study suggests that butterfly space use is influenced by roads and lantana, but the response varies across species. These changes in habitat use might have important population or community-level consequences, such as population declines and shifts in community structure and composition; these need to be further examined.