Distribution Patterns of Impatiens in Sri Lanka: Exploring Niche Breadth, Range Size, and Elevational Dynamics

Abstract

In Sri Lanka, Impatiens (Family Balsaminaceae) is represented by 23 native species, of which 16 are endemic. Additionally, 3 exotic Impatiens are widely cultivated as ornamentals. According to the National Red List 2020, of the native species, 6 are vulnerable (VU), 9 are endangered (EN), 2 are critically endangered (CR) and I. walkeri is listed as critically endangered possibly extinct CR(PE). The present study aimed to analyse the current distribution of Impatiens species across floristic regions and along an elevational gradient in Sri Lanka. Species occurrence data were obtained from reputable repositories such as the National Herbarium, international herbaria, various national and international floristic databases. A georeferenced map was meticulously constructed to evaluate the spatial distribution of these species across distinct floristic zones and along an elevation gradient using ArcGIS Pro and R 4.2.2 version. Heat map analysis and Jaccard clustering based on the distribution of species in different floristic zones were used to detect niche specialty. The central mountains, encompassing the Ramboda-Nuwara Eliya and Adam's Peak floristic zones, exhibited the highest species richness of Sri Lankan Impatiens. Jaccard analysis delineated three primary clusters, none of which included the point endemic species, I. janthina and I. jacobdevlasii. Notably, regression analysis revealed a strong correlation (R2 =+0.7751) between niche breadth and range size, emphasizing the significance of colonizing adaptability in Impatiens species' occupancy patterns. Impatiens acaulis recorded the broadest niche breadth and the largest range size among the species. The optimal elevation range for the majority of Impatiens species was found to be between 1000 and 1200 meters above. Impatiens acaulis and Impatiens cornigera showed distribution patterns that were largely independent of elevation variations. In contrast, I. macrophylla and I. leptopoda exhibited a limited distribution preference especially for highland regions. The findings of the study are expected to be incorporated to conservation attempts of Impatiens species in Sri Lanka.

Keywords: Impatiens, Elevation, Niche, Range, Sri Lanka