Priya Davidar

Why Do Some Tropical Forests Have So Many Species of Trees

Understanding why there are so many kinds of tropical trees requires learning, not only how tree species coexist, but what factors drive tree speciation and what governs a tree clade’s diversification rate. Many report that hybrid sterility evolves very slowly between separated tree populations. If so, tree species rarely originate by splitting of large populations. Instead, they begin with few trees. The few studies available suggest that reproductive isolation between plant populations usually results from selection driven by lowered fitness of hybrids: speciation is usually a response to a “niche opportunity.” Using Hubbell’s neutral theory of forest dynamics as a null hypothesis, we show that if new tree species begin as small populations, species that are now common must have spread more quickly than chance allows. Therefore, most tree species have some setting in which they can increase when rare. Trees face trade-offs in suitability for different microhabitats, different-sized clearings, different soils and climates, and resistance to different pests. These trade-offs underlie the mechanisms maintaining a-diversity and species turnover. Disturbance and microhabitat specialization appear insufficient to maintain a-diversity of tropical trees, although they may maintain tree diversity north of Mexico or in northern Europe. Many studies show that where trees grow readily, tree diversity is higher and temperature and rainfall are less seasonal. The few data available suggest that pest pressure is higher, maintaining higher tree diversity, where winter is absent. Tree a-diversity is also higher in regions with more tree species, which tend to be larger, free for a longer rime from major shifts of climate, or in the tropics, where there are more opportunities for local coexistence.

The Relationship Between Fruit Crop Sizes and Fruit Removal Rates by Birds

It has been proposed that large fruit crops attract disproportionately more frugivores than smaller fruit crops (Snow 1971, Howe and Estabrook 1977). If this is so, then competition between plants for frugivores could be an important source of selection on fruit crop sizes. Field tests of this hypothesis on tropical trees have produced equivocal results (Howe and Smallwood 1982). In six species of fall-fruiting temperate plants, we asked whether the percentage of the fruit that was removed was related to the size of the fruit

Pollination systems of trees in Kakachi, a mid-elevation wet evergreen forest in Western Ghats, India

A long-term survey (1990-2000) of pollination modes of 86 tree species was carried out at Kakachi, a mid-elevation wet forest site in southern Western Ghats, India. Observations were made on 86 tree species. This comprises 80% of the total arborescent species present in the site. Approximately 75% of these species were specialized to a single pollinator group such as bee, beetle, or moth. Pollinators from diverse groups pollinate the remaining 25% of the tree species. Global comparison with other wet forest sites showed that diversity and specialized pollination modes observed in Kakachi bore closer resemblance to other lowland than montane forest sites described so far. However, the number of pollinators involved in pollination was comparable with montane sites. We examine the consequences that might have led to selection of the observed pollination modes in Kakachi. We discuss the conservation implications of these results.

ARE MULTIPLE INFECTIONS MORE SEVERE FOR PURPLE MARTINS (PROGNE SUBIS) THAN SINGLE INFECTIONS

Abstract Between 1986 and 1993, we studied a breeding colony of Purple Martins (Progne subis) in Maryland that were chronically infected with two blood parasites: Haemoproteus prognei, a haematozoan, and an unidentified filarial nematode. We assessed whether cross-infections are more severe than single infections by comparing the return rates of birds infected with either or both parasites and the return rates of uninfected controls. Birds were captured every year and banded, and blood smears were taken for parasite screening. Average prevalence of filaria among the 400 birds screened during this period was 22%. Birds usually became infected by their second year (SY), and infected SY birds had significantly lower return rates than older birds. Cross-infections were rare (8%) and were fatal in 90% of cases. With one exception, birds infected with H. prognei acquired filaria as a second infection, which suggests that although both blood parasites are relatively benign for older Purple Martins, co-infection with a second parasite (in this case, H. prognei) almost always results in death. Est-ce que les Infections Multiples Sont Plus Sévères que les Infections Simples chez Progne subis?

Fruit biomass and relative abundance of frugivores in a rain forest of southern Western Ghats, India

Fruit biomass and frugivore abundance were quantified over 3 y in a rain forest of the south Western Ghats, India. Fruit biomass was estimated by sampling fruit fall in the primary forest, and frugivore abundance by a 2.5-km transect. A total of 645 kg ha -1 of fruit was produced annually in the forest. Only 49% of this is edible to the frugivores and the remaining 51% is in the form of non-edible husks. Mammalian frugivores outnumbered avian frugivores and the majority of the mammals were seed predators. The total fruit biomass produced at Kakachi is lower than in the lowland forest and mountain forests in the neotropics but higher than in the wet sclerophyll forest of Australia. Lower diversity of trees and edaphic factors at Kakachi could be some of the reasons for these differences. On the other hand, paucity of fleshy fruits, low density of trees producing fleshy fruits and irregular fruiting of these species, account for the low number of obligate avian frugivores at Kakachi.

Seed dispersal ecology of a wind dispersed rain forest tree in the Western Ghats, India

Fecundity and seed dispersal of Lophopetalum wightianum, Wight (Celastraceae), a wind dispersed canopy tree species, were studied in the rain forests of the Western Ghats, India. The effects of fruit crop size, seed characteristics, tree height, and wind speed on seedfall and dispersal distances were investigated. Fruiting was synchronous and fruits were produced between February and April. Smaller fruits suffered more predispersal predation. The majority of seeds, described as rolling autogyros were dispersed near the parent. The rate of descent of seeds was related to the square root of wing-loading. However, wind speed significantly decreased the rate of descent and increased dispersal distances. Taller trees dispersed seeds more evenly. Large trees had a significant dispersal advantage since they were more fecund and dispersed seeds further away and more evenly, thereby decreasing the probability of mortality due to density and distance dependent predation. These results show that there is convergence in dispersal strategies of Lophopetalum wightianum with wind dispersed trees studied in the neotropics.

The potential for crop to wild hybridization in eggplant (Solanum melongena; Solanaceae) in southern India.

UNLABELLED • PREMISE OF THE STUDY In India and elsewhere, transgenic Bt eggplant (Solanum melongena) has been developed to reduce insect herbivore damage, but published studies of the potential for pollen-mediated, crop- to- wild gene flow are scant. This information is useful for risk assessments as well as in situ conservation strategies for wild germplasm.• METHODS In 2010-2014, we surveyed 23 populations of wild/weedy eggplant (Solanum insanum; known as wild brinjal), carried out hand-pollination experiments, and observed pollinators to assess the potential for crop- to- wild gene flow in southern India.• KEY RESULTS Wild brinjal is a spiny, low-growing perennial commonly found in disturbed sites such as roadsides, wastelands, and sparsely vegetated areas near villages and agricultural fields. Fourteen of the 23 wild populations in our study occurred within 0.5 km of cultivated brinjal and at least nine flowered in synchrony with the crop. Hand crosses between wild and cultivated brinjal resulted in seed set and viable F1 progeny. Wild brinjal flowers that were bagged to exclude pollinators did not set fruit, and fruit set from manual self-pollination was low. The exserted stigmas of wild brinjal are likely to promote outcrossing. The most effective pollinators appeared to be bees (Amegilla, Xylocopa, Nomia, and Heterotrigona spp.), which also were observed foraging for pollen on crop brinjal.• CONCLUSION Our findings suggest that hybridization is possible between cultivated and wild brinjal in southern India. Thus, as part of the risk assessment process, we assume that transgenes from the crop could spread to wild brinjal populations that occur nearby.

Genetic diversity and population structure of wild/weedy eggplant (Solanum insanum, Solanaceae) in southern India: Implications for conservation

UNLABELLED • PREMISE OF THE STUDY Crop wild relatives represent important genetic resources for crop improvement and the preservation of native biodiversity. Eggplant (Solanum melongena), known as brinjal in India, ranks high among crops whose wild gene pools are underrepresented in ex situ collections and warrant urgent conservation. Knowledge of outcrossing rates and patterns of genetic variation among wild populations can aid in designing strategies for both in situ and ex situ preservation.• METHODS We used 14 microsatellite (simple sequence repeat) markers to examine genetic diversity, population structure, and outcrossing in 10 natural populations of wild/weedy eggplant (S. insanum = S. melongena var. insanum) and three cultivated populations in southern India.• KEY RESULTS Multilocus FST analyses revealed strong differentiation among populations and significant isolation by distance. Bayesian model-based clustering, principal coordinate analysis, and hierarchical cluster analysis grouped the wild/weedy populations into three major clusters, largely according to their geographic origin. The three crop populations were similar to each other and grouped with two wild/weedy populations that occurred nearby. Outcrossing rates among the wild/weedy populations ranged from 5-33%, indicating a variable mixed-mating system.• CONCLUSION Geographic isolation has played a significant role in shaping the contemporary patterns of genetic differentiation among these populations, many of which represent excellent candidates for in situ conservation. In two cases, close genetic affinity between cultivars and nearby wild/weedy populations suggests that gene flow has occurred between them. To our knowledge, this is the first study investigating population-level patterns of genetic diversity in wild relatives of eggplant.

Patterns of butterfly distribution in the Andaman islands: implications for conservation

Twenty-five islands of different sizes were rapidly surveyed in the Andaman islands for patterns of butterfly distribution and abundance. The surveys were conducted in the dry seasons of 1992 in the South Andaman islands, 1994 in the North Andaman islands and on both these years on the Little Andaman Island. Different habitat types were identified on each island and butterflies were sampled by the line transect method in each habitat type. Sixty-five species of butterflies were recorded from six families. Fifty-one species were less common and contributed to 25 % of the total count. Six species were very common. The overall distribution patterns of the species were nested. This suggests that small islands share their species with the larger islands but not vice versa. Many uncommon species were found exclusively on large islands. The presence of evergreen forest on islands significantly influenced the species encountered. Small and medium sized islands with evergreen forests had significantly more species than those without evergreen forests. Loss of primary forests due to logging and encroachment will result in the loss of many butterfly species. It is recommended that the large patches of primary evergreen forests be protected on a priority basis on large islands.

The relationship between area, and vegetation structure and diversity in montane forest (shola) patches in southern India

Background: The montane forests of the higher altitudes of the Western Ghats in southern India, called ‘sholas’, are naturally patchy and closely juxtaposed with grasslands. Palaeoclimatic studies have indicated that the sholas have expanded in warmer climatic regimes and the grasslands during colder climates. Therefore during the present post-glacial climatic regime sholas may be in the expansion phase. Aims: We aimed to test if sholas are in an expansion phase; in particular, if smaller sholas could be at earlier successional stages than larger sholas. Methods: We enumerated all non-climbing plants (≥ 1cm dbh) in 18 shola patches ranging from 0.09ha to 15ha in area. We tested whether species richness, basal area, and proportion of large trees (≥ 30 and ≥ 60cm dbh) increased with shola size, and rare and ‘ecotone’ species decreased with shola size. Results: As predicted, species richness, basal area and the proportion of large trees (≥ 60cm dbh) increased with shola size, whereas the proportion of rare and ‘ecotone’ species decreased with shola size, and species in smaller sholas were a nested subset of those in larger sholas. Conclusions: These results suggest that shola forests are a highly structured plant community, possibly driven by succession.