Functional and phylogenetic approaches reveal the evolution of diversity in a hyper diverse biota

Ant communities in tropical forests may be governed by varying assembly mechanisms, depending on the particular habitat investigated. We compared phylogenetic diversity and structure across two forest biomes (dry and humid) and two vertical layers (arboreal and terricolous) in ant communities in Madagascar, and assessed the influence of invasive species on this community structure. We estimated phylogenetic signal and correlated evolution for habitat and several functional traits and tested for conservatism in relevant functional and habitat traits. Ancestral states were reconstructed to illuminate the evolution of habitat traits. All analyses utilized phylogenies estimated from newly generated data from three nuclear markers for 290 Malagasy ant taxa. Dry forests, although lower in species richness, were found to support equally high lineage diversity as humid forests. In contrast, phylogenetic diversity was much lower in arboreal than in terricolous communities. We observed significant phylogenetic clustering in the combined humid forest and in the arboreal–humid, arboreal–dry and terricolous–humid communities, whereas the combined dry forest community was overdispersed. Among ant communities in Madagascar, overdispersion and competition therefore may be more prevalent in dry forest, and habitat filtering may be more dominant in humid forest. Excluding invasive ant species had little overall effect on community structure. All investigated traits showed low to intermediate conservatism; strong support for correlated evolution was found for increased eye size and an arboreal lifestyle. Habitat transitions from humid to dry and from terricolous to arboreal occurred more frequently, and ancestors of most lineages were predicted to be terricolous or humid‐forest adapted. We conclude that most Malagasy ant clades first colonized humid forests and subsequently transitioned into dry forests, indicating that previous hypotheses on the evolution of Madagascar's hyperdiverse biota may not apply to ants and other arthropods.     

The role of geography and ecological opportunity in the diversification of day geckos (Phelsuma)

We examine the effects of ecological opportunity and geographic area on rates of species accumulation and morphological evolution following archipelago colonization in day geckos (genus Phelsuma) in the Indian Ocean. Using a newly generated molecular phylogeny for the genus, we present evidence that these geckos likely originated on Madagascar, whereas colonization of three archipelagos in the Indian Ocean, the Seychelles, Mascarene, and Comoros Islands has produced three independent monophyletic radiations. We find that rates of species accumulation are not elevated following colonization but are roughly equivalent on all three isolated archipelagos and on the larger island of Madagascar. However, rates of species accumulation have slowed through time on Madagascar. Rates of morphological evolution are higher in both the Mascarene and Seychelles archipelagos compared to rates on Madagascar. This negative relationship between rate of morphological evolution and island area suggests that ecological opportunity is an important factor in diversification of day gecko species.     

Vertical stratification influences global patterns of biodiversity

Species distributions in terrestrial ecosystems are three‐dimensional, spanning both the horizontal landscape and the vertical space provided by the physical environment. Classical hypotheses suggest that communities become more vertically stratified with increasing species richness, owing to reduced competition or finer niche subdivision. However, this assertion remains untested in the context of the broader realm of biogeography. Here, integrating traits and distribution data for amphibians globally, we show how vertical strategies interact with the physical and climatic environments to govern global patterns of species richness and community composition. Our results reveal a marked latitudinal shift in strategies of vertical habitat use, from highly arboreal assemblages in the tropics to highly fossorial assemblages in sub‐tropical and temperate regions. Arboreality is strongly associated with precipitation, vegetation structure and climatic stability, whereas fossoriality is more common in dry environments with high diurnal temperature range and low vegetation structure. These analyses shed light on the importance of vertical stratification for species coexistence in species‐rich regions. As certain tropical habitats become drier from climate change, the rich biological diversity that is emblematic of the tropics may transition from vertically stratified to ‘flattened’, with future communities living mostly on or beneath the ground.     

Immigration, species radiation and extinction in a highly diverse songbird lineage: white-eyes on Indian Ocean islands

Molecular phylogenetic hypotheses of species-rich lineages in regions where geological history can be reliably inferred may provide insights into the scale of processes driving diversification. Here we sample all extant or recently extinct white-eye (Zosterops) taxa of the southwest Indian Ocean, combined with samples from all principal continental lineages. Results support a high dispersal capability, with at least two independent continental sources for white-eyes of the region. An early (within 1.8 million years ago) expansion into the Indian Ocean may have originated either from Asia or Africa; the three resulting lineages show a disparate distribution consistent with considerable extinction following their arrival. Africa is supported as the origin of a later expansion into the region (within 1.2 million years ago). On two islands, a pair of Zosterops species derived from independent immigrations into the Indian Ocean co-occur or may have formerly co-occurred, providing strong support for their origin by double-island colonization rather than within-island (sympatric or microallopatric) speciation. On Mauritius and La Réunion, phylogenetic placement of sympatric white-eyes allow us to rule out a scenario in which independent within-island speciation occurred on both islands; one of the species pairs must have arisen by double colonization, while the other pair is likely to have arisen by the same mechanism. Long-distance immigration therefore appears to be responsible for much of the region's white-eye diversity. Independent immigrations into the region have resulted in lineages with mutually exclusive distributions and it seems likely that competition with congeneric species, rather than arrival frequency, may limit present-day diversity.     

Resource partitioning of sympatric small mammals in an African forest‐grassland vegetation mosaic

It is often hypothesized that two species competing for the same resource cannot stably coexist unless they partition their resources in space and time. More recently stable isotope analyses have complemented traditional, observation‐based niche research by conceptualizing many of the characteristics of communities, for example, trophic niche width and the partitioning of resources. Here we quantify resource partitioning of sympatric small mammal species in an African ecosystem by analysing stable isotope ratios of hair collected from a South African forest‐grassland vegetation mosaic, and combine this with known spatial and temporal behavioural data to interpret community competition and resource partitioning. We observe niche separation to different degrees across the entire community, with different species displaying either unique isotopic dietary preferences, or partitioning resources in space and/or time. δ¹³C values were more enriched in species that inhabited afromontane grassland compared with those that inhabited afromontane forest, a reflection of the dominant vegetation in each habitat. Contrary to expectations, arboreal rodents occupied higher trophic positions than terrestrial rodents and approaching δ¹⁵N values similar to insectivorous shrews, suggesting that arboreal rodents feed on items such as arthropods enriched in ¹⁵N. While grassland species display phenotypic plasticity in terms of dietary preferences, small mammals that occurred in forests display narrow niche preferences, suggesting these species may be particularly sensitive to habitat modifications. Our results illustrate that the use of stable isotopes can be used in conjunction with spatial and temporal behavioural knowledge to elucidate resource partitioning in small African mammal communities.     

Traits reveal how habitat‐quality gradients structure small mammal communities in a fragmented tropical landscape

Understanding the relationships among community structure, vegetation structure and availability of food resources are a key to unravelling the ecological processes that structure biological communities. In this study, we tested (i) whether the composition of small mammal communities changed across gradients in habitat quality in tropical forest fragments, and (ii) whether any observed change could be explained by the functional traits of species. We sampled 24 trapping grids in fragments of semi‐deciduous forest, in each of two 6‐month periods. We considered each trapping grid as a sampling unit, for which we collected three datasets: an environmental matrix (vegetation structure and food resource availability), the abundance of small mammal species (community structure) and a matrix of functional traits (ecological and morphological traits which express tolerance to habitat disturbance and trophic guild). We used an RLQ approach to evaluate the association between traits and environmental gradients. Forest‐specialist and scansorial–arboreal species were associated with more complex habitat that had greater litter and canopy cover and more fallen logs. In relation to trophic guilds, granivore (fruit seeds), insectivorous and omnivorous species were also associated with higher complexity habitat, while frugivores were associated with shrub cover and availability of fruits. We conclude that functional traits (habitat use, use of vertical strata and diet) provide valuable insights into the distribution of small mammals along gradients of habitat quality in tropical forest fragments. We highlight that communities studies in fragmented landscapes should investigate the different components of biodiversity not only in landscape‐scale but also in habitat scale. Abstract in Portuguese is available with online material.     

The ecology of lizards on Praslin Island, Seychelles

Ecological studies of five species of lizards were carried out on the island of Praslin, central Seychelles between July and September 1976. Quadrat sampling within four vegetation types revealed distinct habitat preferences between species. Phelsuma sundbergi occurred at highest densities in coastal vegetation, particularly coconuts Cocos nucifera , whilst Phelsuma astriata occurred at highest densities in intermediate forest, particularly in endemic palms such as Lodoicea maldivica. Within each vegetation type, both species preferred particular tree species. In coastal coconuts and Lodoicea in intermediate forest, the two species tended to occur in different sized trees. Calculations of niche breadth indicated greatest values for P. sundbergi in coastal vegetation and for P. astriata in intermediate forest. Both Phelsuma species showed a diurnal pattern of activity with some indication of temporal displacement between species in lowland and intermediate forest. Ailuronyx sechellensis was nocturnal with a relict distribution on Praslin, occurring in the quadrats on only three endemic palm species in intermediate forest. Mabuya sechellensis was by far the commonest and most widespread of the two skink species, with highest density in intermediate forest where it was probably favoured by the high proportion of palm leaf litter. Scelotes gardineri was only recorded in lowland and intermediate forest, where it occurred at low densities. Both species were diurnal, although the latter was never recorded after midday. Intermediate forest had the highest lizard biomass and species diversity whilst eroded land had the lowest. The possible origins and relationships of the two closely related Phelsuma species are discussed, together with the roles that habitat modification, predation, and interspecific competition may play.     

Interspecific Interactions between Primates,Birds, Bats,and Squirrels May Affect Community Composition on Borneo

For several decades, primatologists have been interested in understanding how sympatric primate species are able to coexist. Most of our understanding of primate community ecology derives from the assumption that these animals interact predominantly with other primates. In this study, we investigate to what extent multiple community assembly hypotheses consistent with this assumption are supported when tested with communities of primates in isolation versus with communities of primates, birds, bats, and squirrels together. We focus on vertebrate communities on the island of Borneo, where we examine the determinants of presence or absence of species, and how these communities are structured. We test for checkerboard distributions, guild proportionality, and Fox's assembly rule for favored states, and predict that statistical signals reflecting interactions between ecologically similar species will be stronger when nonprimate taxa are included in analyses. We found strong support for checkerboard distributions in several communities, particularly when taxonomic groups were combined, and after controlling for habitat effects. We found evidence of guild proportionality in some communities, but did not find significant support for Fox's assembly rule in any of the communities examined. These results demonstrate the presence of vertebrate community structure that is ecologically determined rather than randomly generated, which is a finding consistent with the interpretation that interactions within and between these taxonomic groups may have shaped species composition in these communities. This research highlights the importance of considering the broader vertebrate communities with which primates co‐occur, and so we urge primatologists to explicitly consider nonprimate taxa in the study of primate ecology. Am. J. Primatol. 75:170‐185, 2013. © 2012 Wiley Periodicals, Inc.     

Evidence for habitat partitioning based on adaptation to environmental light in a pair of sympatric lizard species

Terrestrial habitats exhibit a variety of light environments. If species exhibit evolutionary adaptations of their visual system or signals to habitat light conditions, then these conditions can directly influence the structure of communities. We evaluated habitat light characteristics and visual-signal design in a pair of sympatric species of lizards: Anolis cooki and Anolis cristatellus. We found that each species occupies a distinct microhabitat with respect to light intensity and spectral quality. We measured the relative retinal spectral sensitivity and found significant differences between the species that correlate with differences in habitat spectral quality. We measured the spectral reflectance of the dewlaps (colourful throat fans used in communication), and found that the A. cooki dewlap reflects little ultraviolet (UV), while that of A. cristatellus reflects strongly in the UV. For both species downwelling light (irradiance) is rich in UV. However the background light (radiance) is rich in UV for A. cooki, but low in UV for A. cristatellus. Thus, the dewlap of each species creates a high contrast with the background in the UV. Our findings strongly suggest that these two species are partitioning their habitat through specializations of the visual system and signal design to microhabitat light conditions.     

Ecological niche differences betweenAlouatta palliata andCebus capucinus comparing feeding modes,branch use,and diet

During the wet season, two sympatric species of primates,Alouatta palliata (mantled howlers) andCebus capucinus (white-faced capuchins), were assayed for feeding niche differences through behavioral and habitat use patterns at Refugio de Fauna Silvestre Curu in Costa Rica. Differences in the use of relative diameter and thickness of branches and five different modes of feeding were compared between the species. White-faced capuchins used more manipulative modes of obtaining food, a wider range of arboreal habitat, and had a more diverse diet than mantled howlers. Mantled howlers may be more restricted than white-faced capuchins in arboreal microhabitat use due to their possible need for large support branches during feeding bouts and resting periods. We report that differences in feeding behaviors, diet, and arboreal habitat use seem to play a large role in separating these species niches.     

Universal Optimization of Flight Initiation Distance and Habitat-Driven Variation in Escape Tactics in a Namibian Lizard Assemblage

Some aspects of escape predicted by theoretical models are intended to apply universally. For example, flight initiation distance (distance between an approaching predator and prey when escape begins) is predicted from predation risk and the costs of escaping. Escape tactics and refuge selection are not currently predicted by theoretical models, but are expected to vary with structural features of the habitat. One way of studying such variation is to compare aspects of antipredatory behavior among sympatric species that differ in habitat or microhabitat use. In an assemblage of lizards in northwestern Namibia, we conducted experiments to test predictions of escape theory for three risk factors in representatives of three families and observed escape tactics in additional species. As predicted by escape theory, flight initiation distance increased with directness of a predator's approach and predator speed in Agama planiceps, Mabuya acutilabris, and Rhotropus boultoni, and with distance from refuge in M. acutilabris. As predicted by theory, the probability of entering refuge increased with risk in R. boultoni. All available data indicate that flight initiation distance and refuge entry by lizards conform to theoretical predictions. Escape tactics varied greatly as a function of habitat type: (1) arboreal species fled up and around trees and sometimes entered tree holes; (2) saxicolous species used rock crevices as refuges, but differed in tactics prior to entering refuges; and (3) terrestrial species fled into bushes or other vegetation, often to the far sides of them. Some M. acutilabris entered small animal burrows or buried themselves in sand beneath bushes. Escape tactics varied even among congeners in Mabuya, highlighting the important effect of habitat structure on them. Although habitat partitioning has traditionally been viewed as favoring species coexistence, an interesting by‐product appears to be structuring of escape tactics in lizard communities.     

Habitat diversity and species diversity: testing the competition hypothesis with juvenile salmonids

I experimentally tested two predictions of the hypothesis that the positive relationship between habitat diversity and species diversity arises from a reduction in the negative effects of interspecific competition. By allowing species to partition habitat and avoid competition, habitat diversity should 1) facilitate the addition of an ecologically intermediate species into an existing community, and 2) reduce the negative effects of that species on existing members of the community. I tested these predictions with juveniles of three sympatric salmonid species: coho salmon ( Oncorhynchus kisutch ), steelhead trout ( O. mykiss ), and cutthroat trout ( O. clarki ), which in natural streams occupy deep low-velocity pools, shallow high-velocity riffles, and intermediate habitats, respectively. I introduced two (coho and steelhead) and three species communities into each of three artificial stream habitats: pools, riffles, and diverse. The results provide partial support for the predictions. Cutthroat trout grew fastest in the diverse stream habitat. Though habitat diversity did not eliminate the negative effects of competition, in the three species community coho and steelhead grew as fast in the diverse habitat as in either homogeneous habitat. The results are consistent with data on species number and evenness from natural communities, where variation along other niche axes confounds the relationship between habitat diversity, interspecific competition, and species diversity.     

Transitional states in marine fisheries: adapting to predicted global change

Global climate change has the potential to substantially alter the production and community structure of marine fisheries and modify the ongoing impacts of fishing. Fish community composition is already changing in some tropical, temperate and polar ecosystems, where local combinations of warming trends and higher environmental variation anticipate the changes likely to occur more widely over coming decades. Using case studies from the Western Indian Ocean, the North Sea and the Bering Sea, we contextualize the direct and indirect effects of climate change on production and biodiversity and, in turn, on the social and economic aspects of marine fisheries. Climate warming is expected to lead to (i) yield and species losses in tropical reef fisheries, driven primarily by habitat loss; (ii) community turnover in temperate fisheries, owing to the arrival and increasing dominance of warm-water species as well as the reduced dominance and departure of cold-water species; and (iii) increased diversity and yield in Arctic fisheries, arising from invasions of southern species and increased primary production resulting from ice-free summer conditions. How societies deal with such changes will depend largely on their capacity to adapt--to plan and implement effective responses to change--a process heavily influenced by social, economic, political and cultural conditions.     

Toward an identification of resources influencing habitat use in a multi-specific context

Interactions between animal behaviour and the environment are both shaping observed habitat use. Despite the importance of inter-specific interactions on the habitat use performed by individuals, most previous analyses have focused on case studies of single species. By focusing on two sympatric populations of large herbivores with contrasting body size, we went one step beyond by studying variation in home range size and identifying the factors involved in such variation, to define how habitat features such as resource heterogeneity, resource quality, and openness created by hurricane or forest managers, and constraints may influence habitat use at the individual level. We found a large variability among individual's home range size in both species, particularly in summer. Season appeared as the most important factor accounting for observed variation in home range size. Regarding habitat features, we found that (i) the proportion of area damaged by the hurricane was the only habitat component that inversely influenced roe deer home range size, (ii) this habitat type also influenced both diurnal and nocturnal red deer home range sizes, (iii) home range size of red deer during the day was inversely influenced by the biomass of their preferred plants, as were both diurnal and nocturnal core areas of the red deer home range, and (iv) we do not find any effect of resource heterogeneity on home range size in any case. Our results suggest that a particular habitat type (i.e. areas damaged by hurricane) can be used by individuals of sympatric species because it brings both protected and dietary resources. Thus, it is necessary to maintain the openness of these areas and to keep animal density quite low as observed in these hunted populations to limit competition between these sympatric populations of herbivores.     

Divergent habitat use of two urban lizard species

Faunal responses to anthropogenic habitat modification represent an important aspect of global change. In Puerto Rico, two species of arboreal lizard, Anolis cristatellus and A. stratulus, are commonly encountered in urban areas, yet seem to use the urban habitat in different ways. In this study, we quantified differences in habitat use between these two species in an urban setting. For each species, we measured habitat use and preference, and the niche space of each taxon, with respect to manmade features of the urban environment. To measure niche space of these species in an urban environment, we collected data from a total of six urban sites across four different municipalities on the island of Puerto Rico. We quantified relative abundance of both species, their habitat use, and the available habitat in the environment to measure both microhabitat preference in an urban setting, as well as niche partitioning between the two different lizards. Overall, we found that the two species utilize different portions of the urban habitat. Anolis stratulus tends to use more “natural” portions of the urban environment (i.e., trees and other cultivated vegetation), whereas A. cristatellus more frequently uses anthropogenic structures. We also found that aspects of habitat discrimination in urban areas mirror a pattern measured in prior studies for forested sites in which A. stratulus was found to perch higher than A. cristatellus and preferred lower temperatures and greater canopy cover. In our study, we found that the multivariate niche space occupied by A. stratulus did not differ from the available niche space in natural portions of the urban environment and in turn represented a subset of the niche space occupied by A. cristatellus. The unique niche space occupied by A. cristatellus corresponds to manmade aspects of the urban environment generally not utilized by A. stratulus. Our results demonstrate that some species are merely tolerant of urbanization while others utilize urban habitats in novel ways. This finding has implications for long‐term persistence in urban habitats and suggests that loss of natural habitat elements may lead to nonrandom species extirpations as urbanization intensifies.     

Diatoms shape the biogeography of heterotrophic prokaryotes in early spring in the Southern Ocean

The interplay among microorganisms profoundly impacts biogeochemical cycles in the ocean. Culture-based work has illustrated the diversity of diatom–prokaryote interactions, but the question of whether these associations can affect the spatial distribution of microbial communities is open. Here, we investigated the relationship between assemblages of diatoms and of heterotrophic prokaryotes in surface waters of the Indian sector of the Southern Ocean in early spring. The community composition of diatoms and that of total and active prokaryotes were different among the major ocean zones investigated. We found significant relationships between compositional changes of diatoms and of prokaryotes. In contrast, spatial changes in the prokaryotic community composition were not related to geographic distance and to environmental parameters when the effect of diatoms was accounted for. Diatoms explained 30% of the variance in both the total and the active prokaryotic community composition in early spring in the Southern Ocean. Using co-occurrence analyses, we identified a large number of highly significant correlations between abundant diatom species and prokaryotic taxa. Our results show that key diatom species of the Southern Ocean are each associated with a distinct prokaryotic community, suggesting that diatom assemblages contribute to shaping the habitat type for heterotrophic prokaryotes.     

Examining differences in phylogenetic composition enhances understanding of the phylogenetic structure of the shrub community in the northeastern Qinghai‐Tibetan Plateau

Periodic climatic oscillations and species dispersal during the postglacial period are two important causes of plant assemblage and distribution on the Qinghai‐Tibet Plateau (QTP). To improve our understanding of the bio‐geological histories of shrub communities on the QTP, we tested two hypotheses. First, the intensity of climatic oscillations played a filtering role during community structuring. Second, species dispersal during the postglacial period contributed to the recovery of species and phylogenetic diversity and the emergence of phylogenetic overdispersion. To test these hypotheses, we investigated and compared the shrub communities in the alpine and desert habitats of the northeastern QTP. Notably, we observed higher levels of species and phylogenetic diversity in the alpine habitat than in the desert habitat, leading to phylogenetic overdispersion in the alpine shrub communities versus phylogenetic clustering in the desert shrub communities. This phylogenetic overdispersion increased with greater climate anomalies. These results suggest that (a) although climate anomalies strongly affect shrub communities, these phenomena do not act as a filter for shrub community structuring, and (b) species dispersal increases phylogenetic diversity and overdispersion in a community. Moreover, our investigation of the phylogenetic community composition revealed a larger number of plant clades in the alpine shrub communities than in the desert shrub communities, which provided insights into plant clade‐level differences in the phylogenetic structures of alpine and desert shrub communities in the northeastern QTP.     

Vertical stratification of oribatid (Acari: Oribatida) communities in relation to their morphological and life-history traits and tree structures in a subtropical forest in Japan

To clarify the effect of tree structure on the diversity of oribatid mites (Acari: Oribatida), we collected a total of 16,325 oribatids in 181 morphospecies from the leaves, branches, and trunk bark of trees and from the forest-floor soil and litter in a subtropical forest, Okinawa, Japan, and tested three predictions: (1) moisture stress in arboreal habitats would lead to larger body size (not supported); (2) morphological traits related to gripping a surface (number and size of claws) would be more developed in arboreal species (supported); and (3) advantages in colonization (no cost for searching mates and doubled population growth) would favor parthenogenesis in the arboreal oribatid communities (not supported). We observed vertical stratification among the five habitats in terms of mite density, species diversity, and species composition, but found no difference in the body length of oribatid species between the arboreal and forest-floor habitats. However, (homo-)tridactylous species predominated in the arboreal habitat, suggesting that this claw morphology facilitates adherence to and movement on arboreal substrates. Sexual species were common in the arboreal oribatid communities, whereas about half of the dominant species collected from the forest floor were likely to be parthenogenetic. It is unclear how these different reproductive systems may be advantageous for oribatid mites in arboreal and forest-floor habitats. Nevertheless, the structural complexity provided by trees appears to enhance and maintain the diversity of oribatid communities through vertical stratification in this subtropical forest.     

The hypothesis of sympatric speciation as the dominant generator of endemism in a global hotspot of biodiversity

Allopatric or sympatric speciation influence the degree to which closely related species coexist in different manners, altering the patterns of phylogenetic structure and turnover among and between communities. The objective of this study was to examine whether phylogenetic community structure and turnover in the Brazilian Atlantic Forest permit conclusions about the dominant process for the formation of extant angiosperm richness of tree species. Therefore, we analyzed phylogenetic community structure (MPD, MNTD) as well as taxonomic (Jaccard similarity) and phylogenetic turnover (betaMPD, betaMNTD) among and between 49 tree communities distributed among three different habitat types. Mean annual precipitation and mean annual temperature in each survey area were estimated. Phylogenetic community structure does not differ between habitat types, although MPD reduces with mean annual temperature. Jaccard similarity decreases and betaMNTD increases with spatial distance and environmental differences between study sites. Spatial distance explains the largest portions of variance in the data, indicating dispersal limitation and the spatial aggregation of recently formed taxa, as betaMNTD is related to more recent evolutionary events. betaMPD, that is related to deep evolutionary splits, shows no spatial or environmental pattern, indicating that older clades are equally distributed across the Brazilian Atlantic Forest. While similarity pattern indicates dispersal limitations, the spatial turnover of betaMNTD is consistent with a high degree of sympatric speciation generating extant diversity and endemism in the Brazilian Atlantic Forest. More comprehensive approaches are necessary to reduce spatial sampling bias, uncertainties regarding angiosperm diversification patterns and confirm sympatric speciation as the dominant generator for the formation of extant species diversity in the Brazilian Atlantic Forest.     

Origins of mangrove ecosystems and the mangrove biodiversity anomaly

1. Mangrove species richness declines dramatically from a maximum in the Indo-West Pacific (IWP) to a minimum in the Caribbean and Western Atlantic. Explaining this ‘anomalous’ biogeographic pattern has been a focus of discussion for most of this century. 2. Two hypotheses have been put forward to explain the mangrove biodiversity anomaly. The ‘centre-of-origin hypothesis’ asserts that all mangrove taxa originated in the IWP and subsequently dispersed to other parts of the world. The ‘vicariance hypothesis’ asserts that mangrove taxa evolved around the Tethys Sea during the Late Cretaceous, and regional species diversity resulted from in situ diversification after continental drift. 3. Five lines of evidence are used to test between these two hypotheses. First, we review the mangrove fossil record. Second, we compare modern and fossil distributions of mangroves and eight genera of gastropods that show high fidelity to the mangrove environment. Third, we describe species-area relationships of mangroves and associated gastropods with respect to area of available habitat. Fourth, we analyse patterns of nestedness of individual plant and gastropod communities in mangrove forests. Fifth, we analyse patterns of nestedness of individual plant and gastropod species. 4. All five lines of evidence support the vicariance hypothesis. The first occurrences in the fossil record of most mangrove genera and many genera of gastropods associated with mangrove forests appear around the Tethys Sea from the Late Cretaceous through the Early Tertiary. Globally, species richness in any given mangrove forest is tightly correlated with available area. Patterns of nestedness at the community and species-level both point towards three independent regions of diversification of mangrove ecosystems: South-east Asia, the Caribbean and Eastern Pacific, and the Indian Ocean region.