Niche specificity and overlap of threatened angiosperms in the western ghats and its applicability in red list assessment conservation and ecorestoration

Abstract

Industrialization and accelerated climate change pose severe threats to global biodiversity,demanding highly refined, ecologically precise conservation strategies. This doctoralthesis addresses the critical gap between generalised conservation policies and the micro-scale ecological requirements of threatened endemic flora of the Western Ghats usingselected 25 species. These species represent a wide range of Tropical Rainforest types,including low and medium elevation forests, riparian zones, and the Montane Shola-Grassland mosaic. The study’s contribution to threat assessment is evidenced by itsrigorous application of multiple IUCN criteria, which resulted in 15 published and threein-press Red List entries for the focal species. The primary objective was to define theecological niche of these species, niche dynamism of the endemic and restricted taxa andfunctional roles of these species to establish a novel, scientifically grounded frameworkfor ecorestoration planning.The thesis adopts an integrative, multi-facet approach, combining computational and field-based ecology through Species Distribution Modelling (SDM), integrating both Eltonianand Grinnellian factors to produce highly precise predictions of species' realised andfundamental niche ranges. Thiswascomplemented by rigorousfield-basedphytosociological analysis conducted across 126 standardised plots throughout theWestern Ghats. The core methodological advancement was the development of the detailedNiche Profile analysis. This approach empirically quantified the Eltonian niche bymeasuring Importance Value Index (IVI) across all precise functional height classes,enabling a robust assessment of niche specificity and niche overlap. This assessment, usingSchoener's D and Hellinger's I indices, established a strong dual delineation: Grinnellianfactors separated the four major vegetation types, a finding corroborated by speciesdissimilarity indices (90-100% dissimilarity).The analysis revealed significant fine-scale structural and functional partitioning (betadiversity) and a decisive Niche Dichotomy among the endemic flora. High-elevationspecies (Montane Shola guild) exhibited consistently high bioclimatic niche overlap (e.g.,D ~ 0.72 between Strobilanthes kunthiana and Elaeocarpus recurvatus), suggesting theyare Niche Conserved Guilds adapted to a broad Grinnellian niche but differ in Eltonianniche, revealed by niche profiling and face high extrinsic, ecosystem-wide risk.Conversely, low-elevation and specialist species (e.g., Ochna gamblei in coastal sand) demonstrated pronounced niche segregation and low overlap (D ~ 0.20 with other lowelevation and riparian species), classifying them as Niche Specialists with high intrinsicvulnerability driven by specific edaphic, topographical, and hydrological Eltonianconstraints. The data also confirmed the strong functional cohesion of the understoreyrecruitment pool and the high degree of shared niche space among epiphytes, reinforcingthe need for habitat-specific intervention.The findings of the thesis advocates for a strategic, evidence-based policy shift toward anovel Nature-based Solution (NbS) framework utilising this integrated niche modellingand niche profile methodology for conservation planning and ecorestoration of endemictaxa in the tropical rainforest biome. This standardised functional ecorestoration planningframework, which utilises the Niche Profile metrics and the quantitative overlap indices,provides a robust tool for both refining IUCN threat assessments (particularly for high-riskspecialists) and maximising regional Ecosystem-based Adaptation (EbA) outcomes. Byoperationalizing this niche-specific approach, conservation efforts can maximise regionalEbA outcomes, fulfil global Sustainable Development Goals (SDGs), and establish aresilient, scalable management model for threatened tropical rainforest ecosystems.