Biology subjects

Ghuman, S.

Publications and source records attributed to Ghuman, S..

5 recordsLinked to original sources

bioRxiv2026

Frugivore species richness influences dietary specialisation and network properties in Asian wet tropical forests

AimTo examine how variation in frugivore species richness influences dietary specialisation and the organisation of plant-frugivore interaction networks in tropical forests. LocationSix undisturbed lowland wet tropical forest sites across four biodiversity hotspots in south and south-east Asia. Time period2016-2024. Major taxa studiedAvian frugivores and fleshy-fruited woody plants. MethodsWe recorded plant-avian frugivore interactions across six undisturbed evergreen forest sites spanning a seven-fold gradient in frugivore species richness, while holding forest type and phylogenetic composition broadly comparable. Using over 4,200 hours of focal observations on 551 fruiting plants, we recorded more than 34,000 feeding visits by 138 frugivore species on 133 plant species. We used a) Joint species distribution models to determine the relative influence of fruit and seed traits, and b) network analyses to evaluate how dietary breadth and network properties varied with frugivore species richness. ResultsAcross sites, frugivore visitation was primarily explained by fruit and seed morphology, with seed size accounting for an average of 39.7% of explained variation, followed by fruit width (24.4%), fruit crop size (21.9%), and pulp lipid content (14.1%). Frugivores in species-rich communities exhibited narrower dietary breadth (Pearsons r = -0.87 between normalised degree and species richness). Correspondingly, plant-frugivore networks became less connected and nested, and more modular, with increasing frugivore richness (Pearsons r = -0.9, -0.98, and 0.84, respectively). Main conclusionsIncreasing frugivore species richness intensifies dietary specialisation, which in turn drives changes in plant-frugivore network structure. These findings highlight how local species richness shapes interaction networks through changes in consumer niche breadth, with implications for the organisation of tropical forest mutualistic communities.

ecology↗

bioRxiv2025

Comparing the genetic diversity of two threatened Rhyticeros hornbill species with contrasting geographic range sizes

Island endemics exhibit low genetic diversity due to founder effects and geographical isolation, increasing their vulnerability to inbreeding depression. The Narcondam Hornbill (Rhyticeros narcondami), restricted to the 6.8 km2 Narcondam island in the Andaman archipelago, has the smallest range size among hornbills, a globally threatened group of birds. We compared the genetic diversity of the Narcondam Hornbill with the Wreathed Hornbill (Rhyticeros undulatus) distributed from the Eastern Himalaya to Bali. We generated DNA sequences for four mitochondrial markers ; Cytochrome B (Cytb), cytochrome c oxidase subunit I (COI), NADH dehydrogenase subunit 2 (ND2) and displacement loop (D-loop) regions) from 14 Narcondam Hornbill faecal samples and for three markers (Cytb, COI and ND2) from 19 Wreathed Hornbill tissue samples from north-east India. Our results suggest markedly lower genetic diversity in the island endemic Narcondam Hornbill compared to the Wreathed Hornbill. Specifically, Cytb and COI showed no genetic variation in the island endemic, compared to three to five haplotypes in the Wreathed Hornbills. In the ND2 region, Narcondam Hornbills showed seven haplotypes among 13 samples compared to the Wreathed Hornbills six haplotypes among eight samples. The observed genetic diversity in the D-loop in the Narcondam Hornbill was lower than other island-endemic hornbill species in the Philippines. The extremely low genetic diversity in the Narcondam Hornbill likely stems from a small founder population and/or past hunting pressures that reduced its numbers to approximately 30% of its current population of 1000 birds, rendering the Narcondam Hornbill susceptible to environmental and human-driven changes.

genetics↗

bioRxiv2025

Effects of frugivore species pool and seed size on the diversity and functional composition of frugivores visiting fruiting trees

The relationship between biodiversity and ecosystem functioning in seed dispersal remains understudied despite its critical role in maintaining plant diversity in the tropics. Field studies on this relationship are often confounded by environmental and phylogenetic variations across species richness gradients. We examined how overall avian frugivore species richness at a site influenced the frugivore richness, visitation rates and functional composition of two key effect traitsbeak width and hand-wing indexon fruiting trees. Across six sites in tropical Asia, spanning a sevenfold gradient in frugivore species richness but with similar forest types and phylogenetically nested frugivore communities, we recorded 34,014 interactions between 134 avian frugivores and 131 plant species. Our results provide some support for the biodiversity-ecosystem functioning relationship, as higher overall frugivore species richness increased the number of frugivore species visiting individual fruiting trees but not the functional composition of frugivores. Seed size had a stronger influence on the frugivore species richness, visitation rates, and the beak size of visiting frugivores, highlighting the dominant role of morphological trait matching in influencing plant-frugivore interactions. Our findings suggest functional redundancy in certain aspects of seed dispersal effectiveness due to density compensation and the presence of key seed disperser lineages in species-poor sites.

ecology↗

bioRxiv2023

Frugivory and seed predation of fishtail palm (Caryota mitis Lour.) on the remote oceanic island of Narcondam, India

Oceanic islands, due to their evolutionary history and isolation, hold a disproportionately high proportion of endemic species. However, their evolutionary history also makes them vulnerable to extinctions, with most known extinctions occurring on islands. Plant-animal interactions are particularly important on islands, as island systems generally have low redundancy and are more vulnerable to disruption either via extinction or by invasive species. Here, we examined the fruit removal and seed predation of a keystone palm, Caryota mitis, on the remote oceanic island of Narcondam. The island endemic Narcondam hornbill (Rhyticeros narcondami), was the sole seed disperser of the Caryota mitis (90 hours; N = 15 trees), indicating a lack of redundancy in seed dispersal of the palm on this island. While the invasive rodent, Rattus cf. tiomanicus was the sole predator of the Caryota mitis seeds in the forest (N = 15 individual fruiting palms, 416 trap nights). Overall, 17.1% of the seeds placed (N = 375 seeds) were removed. Seeds placed under and away from the canopy, and at different densities (2 plots with 10 seeds each; 1 plot with 5 seeds, respectively), showed similar removal rates. This is indicative of ambient seed predation and the lack of safe sites for the regeneration of Caryota mitis, with potential deleterious effects on the subsequent stages of the "seed dispersal cycle". Here, from a data deficient site, we provide baseline information on the plant-frugivore interaction of a keystone palm and the potential impacts by an invasive rodent.

ecology↗

bioRxiv2020

The critical ecological role of an endemic, large-bodied frugivore on a small tropical island

Endozoochory, a mutualistic interaction between plants and frugivores, is one of the key processes responsible for maintenance of tropical biodiversity. Islands, which have a smaller subset of plants and frugivores when compared with mainland communities, offer an interesting setting to understand the organization of plant-frugivore communities vis-a-vis the mainland sites. We examined the relative influence of functional traits and phylogenetic relationships on the plant-seed disperser interactions on an island and a mainland site. The island site allowed us to investigate the organization of the plant-seed disperser community in the natural absence of key frugivore groups (bulbuls and barbets) of Asian tropics. The endemic Narcondam Hornbill, was the most abundant frugivore on the island and played a central role in the community. Species strength, a measure of relevance of frugivores for plants, of frugivores was positively associated with their abundance. Among plants, figs had the highest species strength and played a central role in the community. Island-mainland comparison revealed that the island plant-seed disperser community was more asymmetric, connected and nested as compared to the mainland community. Neither phylogenetic relationships or functional traits (after controlling for phylogenetic relationships) were able to explain the patterns of interactions between plants and frugivores on the island or the mainland pointing towards the diffused nature of plant-frugivore interactions. The diffused nature is a likely consequence of plasticity in foraging behavior and trait convergence that contribute to governing the interactions between plants and frugivores.

ecology↗