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Author

Shivani Krishna

Other affiliations: Indian Institute of Science
Bio: Shivani Krishna is an academic researcher from Indian Institute of Science Education and Research, Thiruvananthapuram. The author has contributed to research in topics: Pollination & Pollinator. The author has an hindex of 3, co-authored 5 publications receiving 28 citations. Previous affiliations of Shivani Krishna include Indian Institute of Science.

Papers
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Journal ArticleDOI
TL;DR: A concise review of the state of the authors' knowledge on the evolution of floral traits and pollinator sensory perception and how these together shape the structure and organization of pollination networks is provided.
Abstract: Communication of any sort is complex and communication between plants and animals is particularly so. Plant-pollinator mutualisms are amongst the most celebrated partnerships that have received a great deal of attention for many centuries. At the outset, most pollination studies focused on phenotypic matches and invoked co-evolution to explain plant- pollinator interactions, which gave rise to the concept of pollination syndromes. A few centuries later, there has been a substantial shift in the way we view these mutualistic interactions. In a significant departure from a co-evolutionary framework, numerous studies subsequently showed that there is usually only a loose, non-exclusive matching between flowers and their pollinators. Concurrently, the global prevalence of generalized pollination systems was demonstrated repeatedly. However, our understanding of the evolutionary processes that underlie these mutualisms is still limited. Here, we provide a concise review of the state of our knowledge on the evolution of floral traits and pollinator sensory perception and how these together shape the structure and organization of pollination networks.

14 citations

Journal ArticleDOI
TL;DR: It is predicted that nocturnal bees primarily use night-blooming flowers, show little/no resource overlap with diurnal species and competitive release favors night-time pollen collection for provisioning, and found substantial resource overlap betweennocturnal and diurnal bees.
Abstract: 1. Bees exemplify flights under bright sunlight. A few species across bee families have evolved nocturnality, displaying remarkable adaptations to overcome limitations of their daylight-suited apposition eyes. Phase inversion to nocturnality in a minority of bees that co-exist with diurnal bees provide a unique opportunity to study ecological benefits that mediate total temporal niche shifts. While floral traits and sensory modalities associated with the evolution of classical nocturnal pollination syndromes, e.g. by bats and moths, are well-studied, nocturnality in bees represent a poorly understood, recently invaded, extreme niche. 2. To test the competitive release hypothesis, we examine how nocturnality shapes foraging by comparing pollen loads, nest pollen and flower visitation of sympatric nocturnal and diurnal carpenter bees. We predicted that nocturnal bees primarily use night-blooming flowers, show little/no resource overlap with diurnal species and competitive release favours night-time pollen collection for provisioning. 3. Contrarily, we found substantial resource overlap between nocturnal and diurnal bees. Flower opening times, floral longevity and plant abundance did not define nocturnal flower use. Smaller pollen loads on nocturnal foragers suggests subsistence on resource leftovers largely from diurnal flowers. Greater pollen types/diversity on nocturnal foragers indicates lower floral constancy compared to diurnal congenerics. Reduced activity during new moon compared to full moon suggests constraints to nocturnal foraging. 4. Invasion and sustenance within the nocturnal niche is characterised by: i)opportunistic foraging on residual resources as indicated by smaller pollen loads, extensive utilisation of day-blooming flowers and substantial overlap with diurnal bees, ii)generalisation at two levels – between and within foraging trips as indicated by lower floral constancy, iii)reduced foraging on darker nights, indicating visual constraints despite sensitive optics. This together with smaller populations and univoltine breeding in nocturnal compared to multivoltine diurnal counterparts, suggest that nocturnality imposes substantial fitness costs. 5. In conclusion, the evolution of nocturnality in bees is accompanied by resource generalisation instead of specialisation. Reduced floral constancy suggests differences in foraging strategies of nocturnal and diurnal bees which merits further investigation. The relative roles of competition, floral rewards and predators should be examined to fully understand the evolution and maintenance of nocturnality in bees.

12 citations

Journal ArticleDOI
TL;DR: In these fragmented swamp forests, secondary removal by crabs retains seeds largely within the swamps, where conditions for their establishment and survival are optimal, and could provide temporal and spatial refugia from seed predators such as rodents in Myristica fatua.
Abstract: Little is known about the role of crabs as seed dispersers and predators. Recently, there has been interest in understanding their influence on plant recruitment in coastal forests. Secondary seed removal by crabs in a swamp-specialist tree, Myristica fatua, was investigated in the rare and patchy freshwater Myristica swamps in the Western Ghats in India. Tethered-line experiments were used to determine the role of crabs as secondary seed-removal agents in two study sites. Crabs transported a large percentage (63.3%) of seeds (n = 60) placed on the forest floor compared with rodents (25%) and other unknown agents (13.3%). Simultaneous choice experiments suggested that the nutrient-rich arils covering seeds were consumed, but there was no evidence for seed predation by crabs. A small percentage (13.3%) of monitored seeds (n = 60) germinated from within crab burrows. The spatial scale of secondary removal by crabs was restricted to < 10 m. In these fragmented swamp forests, secondary removal by crabs retains seeds largely within the swamps, where conditions for their establishment and survival are optimal. Thus, secondary seed removal by crabs could provide temporal and spatial refugia from seed predators such as rodents in Myristica fatua.

9 citations

Journal ArticleDOI
TL;DR: Using a model of honeybee color vision, the distance between the color loci of male and female flowers is found and based on minimum visual angle subtended by these flowers, it is suggested that the two floral sexes cannot be discriminated by bees.
Abstract: Myristica fatua is a dioecious specialist species restricted to the endangered, freshwater Myristica swamp forests in the Western Ghats, India. Earlier studies have alluded to pollination by deception in members of the Myristica genus, and thus we examined the pollination ecology comprising floral biology, flower production, flower visitors, and reproductive success in M. fatua and inferred the potential strategies that could permit such deception in this habitat specialist tree. Male flowers provide pollen rewards for an extended period of time while female flowers are rewardless and both sexes are visited by generalist insects, mainly by honeybees and stingless bees. Bee visits were significantly more frequent and longer on male than on female flowers as bees collected pollen from male flowers. We found that flower production patterns create a preponderance of males compared to females in the swamp populations. Using a model of honeybee color vision, we found the distance between the color loci of male and female flowers and based on minimum visual angle subtended by these flowers, we suggest that the two floral sexes cannot be discriminated by bees. Bees are likely deceived by the perceptual similarity of rewardless female flowers to pollen-offering male flowers and pollination is the consequence of foraging errors made by pollinators that encounter largely male–rarely female flower mosaics as they forage among clump-distributed M. fatua trees in the swamp habitat.

3 citations

Journal ArticleDOI
TL;DR: It is found that M. fatua bears few large-sized seeds and fruits for extended periods of time such that few seeds are produced at any point of time, thus escaping detection of seed predators.
Abstract: Our understanding of processes underlying plant recruitment emerges from species and habitats that are widely distributed at regional and global scales. However, the applicability of dispersal-recruitment models and the role of dispersal limitation versus microsite limitation have not been examined for specialized habitats. In patchy, freshwater Myristica swamp forests (Western Ghats, India), we examine the roles of primary seed dispersal, secondary seed removal and microsite suitability for the establishment of a swamp specialist tree, Myristica fatua We estimated primary seed shadows, performed secondary removal experiments and enumerated recruits in swamp sites. Steady-state fruiting was observed with the extended production (>7 months) of small numbers of fruits. Frugivores dropped most of the large and heavy seeds under parent crowns, while a few seeds were transported over short distances by hornbills. Seed placement experiments indicated that removal, germination and establishment were similar within swamp microsites, while seeds failed to survive in matrix habitats surrounding the swamp. Crabs, which were major secondary removers of M. fatua, did not alter the initial seed dispersal patterns substantially, which led to the retention of seeds within the swamp. Distribution of saplings and adults from previous seasons also suggest that dispersal-recruitment dynamics in the swamp specialist M. fatua did not strictly follow predictions of Janzen-Connell model while abiotic effects were significant. Large seeds, steady-state fruiting and small crop sizes may be significant selective forces facilitating escape from density and distance-dependent effects in space and time in specialist plant species such as M. fatua.

2 citations


Cited by
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Journal ArticleDOI
TL;DR: The review demonstrates that synzoochory is pivotal to the functioning of many ecosystems where the natural regeneration of keystone plant species depends on the activity of granivorous animals that play a dual role, and finds that synZoochorous interactions are widely spread across the mutualism–antagonism continuum.
Abstract: J.M.G. and P.J. were supported by CYTED program (Red Tematica 418RT0555). E.W.S. is supported by the Ecology Center and the Utah Agricultural Experiment Station (UAES), Utah State University. P.J. is supported by grant CGL2017‐82847‐P from the Spanish Ministry of Science, Innovation, and Universities (AEI).

102 citations

Journal ArticleDOI
TL;DR: Flying foxes play a vital function in dispersing seeds within a Pacific archipelago, but more than 75% of plant species eaten by flying foxes, and that had large fruits, were not dispersed effectively by any other animal.
Abstract: The low species diversity that often characterizes island ecosystems could result in low functional redundancy within communities. Flying foxes (large fruit bats) are important seed dispersers of large-seeded species, but their redundancy within island communities has never been explicitly tested. In a Pacific archipelago, we found that flying foxes were the sole effective disperser of 57 % of the plant species whose fruits they consume. They were essential for the dispersal of these species either because they handled >90 % of consumed fruit, or were the only animal depositing seeds away from the parent canopy, or both. Flying foxes were especially important for larger-seeded fruit (>13 mm wide), with 76 % of consumed species dependent on them for dispersal, compared with 31 % of small-seeded species. As flying foxes decrease in abundance, they cease to function as dispersers long before they become rare. We compared the seed dispersal effectiveness (measured as the proportion of diaspores dispersed beyond parent crowns) of all frugivores for four plant species in sites where flying foxes were, and were not, functionally extinct. At both low and high abundance, flying foxes consumed most available fruit of these species, but the proportion of handled diaspores dispersed away from parent crowns (quality) was significantly reduced at low abundance. Since alternative consumers (birds, rodents and land crabs) were unable to compensate as dispersers when flying foxes were functionally extinct, we conclude that there is almost no redundancy in the seed dispersal function of flying foxes in this island system, and potentially on other islands where they occur. Given that oceanic island communities are often simpler than continental communities, evaluating the extent of redundancy across different ecological functions on islands is extremely important.

58 citations

Journal ArticleDOI
TL;DR: Pollinating insects exploit visual and olfactory cues associated with flower traits indicative of flower location and reward quality to induce changes in these flower‐associated cues, thereby influencing the behaviour of flower visitors.
Abstract: 1. Pollinating insects exploit visual and olfactory cues associated with flower traits indicative of flower location and reward quality. Pollination can induce changes in these flower-associated cues, thereby influencing the behaviour of flower visitors. 2. This study investigated the main cues exploited by the syrphid fly Episyrphus balteatus and the butterfly Pieris brassicae when visiting flowers of Brassica nigra and Raphanus sativus plants. Whether pollen is used as a cue and whether pollination-induced changes affect flower volatile emission and the behavioural responses of the two pollinator species were also studied. 3. Pollinator preference was investigated by offering visual and olfactory cues individually as well as simultaneously in two-choice bioassays. Plant treatments included emasculation, hand-pollination and untreated control plants. The composition of flower volatiles from pollinated and unpollinated control plants was analysed by gas chromatography-mass spectrometry. 4. Both pollinators exhibited a strong bias for visual cues over olfactory cues. Neither pollinator used pollen as a cue. However, E. balteatus discriminated between newly opened and long-open flowers at short distance only when pollen was available. Flower visits by pollinators were influenced by pollination-induced changes in B. nigra but not R. sativus flowers. Pieris brassicae only responded to pollination-induced changes when visual and olfactory cues were offered simultaneously. The blend of volatiles emitted by B. nigra, but not R. sativus inflorescences was affected by pollination. 5. Collectively, the findings of this study show that different pollinators exploit different visual and olfactory traits when searching for flowers of two brassicaceous plant species.

24 citations