Influence of invasive plant species on native plant-flower visitor interactions in a scrub forest of Anaikatty, Nilgiri Biosphere Reserve

Abstract

Invasive alien species are one of the top five drivers of biodiversity loss globally. Invasive alien species are known to cause changes to the biotic interactions in the invaded regions. Pollination is an important limiting process in the life cycle of plants and the pollinators potentially mediate the process of invasion through novel interactions. Invasive plants can have an impact on the native plant-pollinator interactions. 2. I studied the influence of invasive plants on the native plant-flower visitor interactions in the scrub forests of Anaikatty, Nilgiri Biosphere Reserve. I determined the change in flower visitor diversity along an invasion gradient. I also compared the visitation between native and invasive plants, by looking at the difference in composition of insect interactions with native and invasive plants. I used 20 min zigzag walks in 26 plots across three months looking at insects interacting with flowers. I also estimated the density of flowers in each plot. 3. I used generalised linear mixed effects models to draw the relationship between insect richness and the proportion of invasive flowers, and between number of visits and proportion of invasive flowers. To compare the difference in composition of flower visitors between the plant species, I performed permutational multivariate analysis of variance (PERMANOVA) with bray-curtis dissimilarity index. 4.I observed 191 unique plant-flower visitor interactions of a total of 813 plant-flower visitor interactions, formed by 68 insect visitors and 28 flowering plants. Native plants, Sida cordifolia (25%), Tephrosia purpurea (20%) and Glycosmis mauritiana (13%) and invasive plants Parthenium hysteriphorus (8%) and Ageratum conyzoides (6%) formed majority of the interactions. Hymenoptera and Lepidoptera are the insect orders with the most number of interactions. 5. The richness and number of flower visitors increase with increasing flower density. The richness and number of flower visitors show a negative relationship with proportion of invasive flowers. The composition of visitors is significantly ifferent among all native flowers and between native flowers and invasive flowers.6.This is the first study in the Nilgiris Biosphere Reserve looking at plant-flower visitor interactions in wild flowers, with a focus on the influence of invasive species. Visitation of insects to a plot has a weak negative relationship with proportion of invasive species, in this context. This study sets the baseline for future studies that could look at explaining the patterns seen, looking at relationship between the functional diversity of flowers and insects.