When are phylogenetic analyses misled by convergence? A case study in Texas cave salamanders

Convergence, i.e., similarity between organisms that is not the direct result of shared phylogenetic history (and that may instead result from independent adaptations to similar environments), is a fundamental issue that lies at the interface of systematics and evolutionary biology. Although convergence is often cited as an important problem in morphological phylogenetics, there have been few well-documented examples of strongly supported and misleading phylogenetic estimates that result from adaptive convergence in morphology. In this article, we propose criteria that can be used to infer whether or not a phylogenetic analysis has been misled by convergence. We then apply these criteria in a study of central Texas cave salamanders (genus Eurycea). Morphological characters (apparently related to cave-dwelling habitat use) support a clade uniting the species E. rathbuni and E. tridentifera, whereas mitochondrial DNA sequences and allozyme data show that these two species are not closely related. We suggest that a likely explanation for the paucity of examples of strongly misleading morphological convergence is that the conditions under which adaptive convergence is most likely to produce strongly misleading results are limited. Specifically, convergence is most likely to be problematic in groups (such as the central Texas Eurycea) in which most species are morphologically very similar and some of the species have invaded and adapted to a novel selective environment.     

Convergence and the multidimensional niche

Convergent evolution has played an important role in the development of the ecological niche concept. We investigated patterns of convergent and divergent evolution of Caribbean Anolis lizards. These lizards diversified independently on each of the islands of the Greater Antilles, producing the same set of habitat specialists on each island. Using a phylogenetic comparative framework, we examined patterns of morphological convergence in five functionally distinct sets of morphological characters: body size, body shape, head shape, lamella number, and sexual size dimorphism. We find evidence for convergence among members of the habitat specialist types for each of these five datasets. Furthermore, the patterns of convergence differ among at least four of the five datasets; habitat specialists that are similar for one set of characters are often greatly different for another. This suggests that the habitat specialist niches into which these anoles have evolved are multidimensional, involving several distinct and independent aspects of morphology.     

Lack of convergence in aquatic Anolis lizards

Why convergent evolution occurs among some species occupying similar habitats but not among others is a question that has received surprisingly little attention. Caribbean Anolis lizards, known for their extensive convergent evolution among islands in the Greater Antilles, are an appropriate group with which to address this question. Despite the well-documented pattern of between-island convergence, some Greater Antillean anoles are not obviously part of the convergence syndrome. One example involves aquatic anoles--species that are found near to and readily enter streams-which have evolved independently twice in the Caribbean and also twice on mainland Central America. Despite being found in similar habitats, no previous study has investigated whether aquatic anoles represent yet another case of morphological convergence. We tested this hypothesis by collecting morphological data for seven aquatic anole species and 29 species from the six convergent types of Greater Antillean habitat specialists. We failed to find evidence for morphological convergence: the two Caribbean aquatic species are greatly dissimilar to each other and to the Central American species, which, however, may be convergent upon each other. We suggest two possible reasons for this lack of convergence in an otherwise highly convergent system: either there is more than one habitat type occupied by anoles in the proximity of water, or there is more than one way to adapt to a single aquatic habitat. We estimate that almost all of the 113 species of Greater Antillean anoles occupy habitats that are also used by distantly related species, but only 15% of these species are not morphologically similar to their distantly related ecological counterparts. Comparative data from other taxa would help enlighten the question of why the extent of convergence is so great in some lineages and not in others.     

Measuring size and composition of species pools: a comparison of dark diversity estimates

Ecological theory and biodiversity conservation have traditionally relied on the number of species recorded at a site, but it is agreed that site richness represents only a portion of the species that can inhabit particular ecological conditions, that is, the habitat‐specific species pool. Knowledge of the species pool at different sites enables meaningful comparisons of biodiversity and provides insights into processes of biodiversity formation. Empirical studies, however, are limited due to conceptual and methodological difficulties in determining both the size and composition of the absent part of species pools, the so‐called dark diversity. We used >50,000 vegetation plots from 18 types of habitats throughout the Czech Republic, most of which served as a training dataset and 1083 as a subset of test sites. These data were used to compare predicted results from three quantitative methods with those of previously published expert estimates based on species habitat preferences: (1) species co‐occurrence based on Beals' smoothing approach; (2) species ecological requirements, with envelopes around community mean Ellenberg values; and (3) species distribution models, using species environmental niches modeled by Biomod software. Dark diversity estimates were compared at both plot and habitat levels, and each method was applied in different configurations. While there were some differences in the results obtained by different methods, particularly at the plot level, there was a clear convergence, especially at the habitat level. The better convergence at the habitat level reflects less variation in local environmental conditions, whereas variation at the plot level is an effect of each particular method. The co‐occurrence agreed closest the expert estimate, followed by the method based on species ecological requirements. We conclude that several analytical methods can estimate species pools of given habitats. However, the strengths and weaknesses of different methods need attention, especially when dark diversity is estimated at the plot level.     

The phylogenetic structure of habitat shift and morphological convergence in Asian Clarias (Teleostei, Siluriformes: Clariidae)

Catfishes of the genus Clarias are an important component of the ichthyofauna in Asia and in Africa. Previous studies demonstrated a high diversity in number of species, morphology and habitat, but little was known on the evolutionary processes underlying this diversity. We analysed an original data set of molecular sequences (cytochrome b and 16S genes), habitat and geographic distributions, as well as 29 morphometric measurements taken on 454 specimens of Asian Clarias . Maximum likelihood phylogeny estimation showed an unexpected cryptic diversity due to strong morphological convergence. The patterns of intra- and interspecific phylogenetic divergence are overall explained by geographic isolation. The analysis of habitat transitions with Markovian models showed that Asian Clarias evolved from an ancestor probably living in clear waters. The most frequent transitions occurred between clear and white waters, whereas transitions towards black waters occurred only from clear waters and were rare events. The morphometric analysis suggests a complex pattern of morphological evolution with repeated convergence towards an elongated form in black waters. The phylogeographic patterns of diversification of Asian Clarias agree with previous studies on other groups and the hypothesis that changes in sea level during the Pleistocene had little influence on shaping biodiversity on the Sunda Shelf.     

Nonrandom larval dispersal can steepen marine clines

Sharp and stable clinal variation is enigmatic when found in species with high gene flow. Classical population genetic models treat gene flow as a random homogenizing force countering local adaptation across habitat discontinuities. Under this view, dispersal over large spatial scales will lower the effectiveness of adaptation by natural selection at finer spatial scales. Thus, random gene flow will create a shallow phenotypic cline across an ecotone in response to a steep selection gradient. In sedentary marine species that disperse primarily as larvae, nonrandom dispersal patterns are expected due to coastal hydrodynamics. Surprisingly sharp phenotypic and genotypic clines have been documented in marine species with high gene flow. We are interested in the extent to which nonrandom dispersal could accentuate such clines. We model a linear species range in which populations have stable and uniform densities along a selection gradient; in contrast to random dispersal, convergent advection of larvae can amplify phenotypic differentiation if coupled with a semipermeable dispersal barrier in the convergence zone. The migration load caused by directional dispersal pushes the phenotypic mean away from the local trait optimum in downstream populations, that is, near the convergence zone. A dispersal barrier is possible as a result of colliding currents if the water and larvae are mostly displaced offshore, away from suitable settlement habitat. Disjunctions in a quantitative trait were enlarged in the convergence zone by faster current flows or a more complete dispersal barrier. With advection of larvae per generation one-third as far as the average dispersal distance by diffusion, convergence on a dispersal barrier with 40% permeability generated a trait disjunction across the convergence zone of two phenotypic standard deviations. Without directional dispersal, similar clines also developed across a habitat gap, where population density was low, or across dispersal barriers with less than 1% permeability. These findings suggest that the types of hydrographic phenomena often associated with marine transition zones can strongly affect the balance between gene flow and selection and generate surprisingly steep clines given the large-scale gene flow expected from larvae.     

Regional environments, life-history patterns, and habitat use of spirostreptid millipedes in arid regions

Among diplopods with desert populations, only three species of Spirostreptida have been studied in an ecological context. The present review compares regional environments, life-history patterns, and uses of habitat by Orlhoporus ornatus (Girard) from southwestern North America, Archispirostreptus tumuliporus judaicus (Attems) from the eastern Mediterranean seaboard, and Harpagophora nigra (Attems) from southwestern Africa. Published and unpublished studies are used to explore evidence for convergence among these species, as opposed to traits adapting them to physical aspects of given regions or habitats. Unlike A. t. judaicus, O. ornatus and H. nigra are relatively restricted to arid habitats, although populations of all three species experience a variety of rainfall regimes and regional topographies. Where studied, O. ornatus and H. nigra hibernate during the long, often cool or cold dry season; they forage following warm-season rains. A. t. judaicus , in contrast, forages during its long, warm dry season and hibernates in the cool, wet winter. Populations from the Judaean and Negev deserts differ from those inhabiting a mesic habitat (Megiddo) closer to the coast in regard to rates of development, seasonal activity and seasonal water balance. Convergence in the form of well-developed desiccation resistance characterizes the two strictly desert species. All three species, together with other subtropical millipedes exposed to long dry seasons, are convergent with respect to patterns of diel surface activity and use of shelter. However species- and habitat-specific life-history features such as the seasonal timing of dormancy and emergence tend to mask convergence at the habitat level. Hence, the independent evolution of the three species with desert populations has resulted in life histories and habitat use that combine a moderate amount of convergence with considerable opportunistic adaptation to regional and local conditions.     

POPULATION STUDIES AMONG SONORAN DESERT SPECIES OF PARMELIA SUBG. XANTHOPARMELIA (PARMELIACEAE)

Species of Parmelia subg. Xanthoparmelia exhibit partial morphological convergence in a region of sympatry in the northern portion of the Sonoran Desert. Within the isidiate morph of the population, chemotypic variation is present. These chemotypes exhibit habitat selection among different rock substrates within a region of relatively uniform climate and topography. Partial habitat selection is also demonstrable for the chemotypes of the nonisidiate morph in the population. Other morphological characters are useful in segregating portions of the isidiate and nonisidiate morphs into chemically distinct groups that have previously been assumed to represent only chemotypic variation.     

The Interplay between Environmental Filtering and Spatial Processes in Structuring Communities: The Case of Neotropical Snake Communities

Both habitat filters and spatial processes can influence community structure. Space alone affects species immigration from the regional species pool, whereas habitat filters affect species distribution and inter-specific interactions. This study aimed to understand how the interplay between environmental and geographical processes influenced the structure of Neotropical snake communities in different habitat types. We selected six studies that sampled snakes in forests, four conducted in savannas and two in grasslands (the latter two are grouped in a non-forest category). We used the net relatedness and nearest taxon indices to assess phylogenetic structure within forest and non-forest areas. We also used the phylogenetic fuzzy-weighting algorithm to characterize phylogenetic structure across communities and the relation of phylogenetic composition patterns to habitat type, structure, and latitude. Finally, we tested for morphological trait convergence and phylogenetic niche conservatism using four forest and four non-forest areas for which morphological data were available. Community phylogenetic composition changed across forest and non-forest areas suggesting that environmental filtering influences community structure. Species traits were affected by habitat type, indicating convergence at the metacommunity level. Tail length, robustness, and number of ventral scales maximized community convergence among forest and non-forest areas. The observed patterns suggested environmental filtering, indicating that less vertically structured habitats represent a strong filter. Despite the fact that phylogenetic structure was not detected individually for each community, we observed a trend towards communities composed by more closely related species in higher latitudes and more overdispersed compositions in lower latitudes. Such pattern suggests that the limited distribution of major snake lineages constrained species distributions. Structure indices for each community were also related to habitat type, showing that communities from non-forest areas tend to be more clustered. Our study showed that both environmental filtering and spatial gradients play important roles in shaping the composition of Neotropical snake communities.     

A metacommunity ecological approach to understanding the community organization of fish in artificial ponds of the Mamoré River floodplain in the Amazonian lowlands of Bolivia

The origin and maintenance of biodiversity and the influence of human activities on biodiversity are issues of central interest to scientists as well as policymakers. We conceptualized the integration of metacommunity paradigms across space and time to better understand the community organization of fish under the hydrological control mechanisms of large river floodplains. In our analysis of variation partitioning and functional ecology, patchy dynamics and mass effects represent special cases of species-sorting paradigms generated by neutral processes in certain species, and the relative roles of neutral processes and local adaptations may increase along with the spatio-temporal extent. The effect of flood event timing, floodplain elevation and vegetation cover on species abundance determined the distribution of seasonal patchy heterogeneous habitats. Spatio-temporal structures were observed among patches of the same habitat types across years but within habitat patches in the same year. The convergence of life history traits and respiratory modes of species associated with different habitat types was not significant, and traits could present overall seasonality within patches and segregation among patches of the same habitat types across years. Furthermore, the similarity of these traits was explained by phylogenetic relationships. At the spatio-temporal scale of the present study, the origin of lineage-specific allometric effects in fish, the origin of habitat specialization and their consequences for metacommunity dynamics were not clear. These results are most likely related to species-sorting processes, in which the species adapted to a specific type of habitat ex situ subsequently colonized an area after it was altered via human activities.     

BEHAVIORAL CONVERGENCE AND ADAPTIVE RADIATION: EFFECTS OF HABITAT USE ON TERRITORIAL BEHAVIOR IN ANOLIS LIZARDS

Most studies of adaptive radiations focus on morphological aspects of differentiation, yet behavior is also an important component of evolutionary diversification, often mediating the relationship between animal ecology and morphology. In species within radiations that are convergent in ecology and morphology, we then also expect convergence in behavior. Here, we examined 13 Anolis lizard species to determine whether territorial strategies have evolved convergently with morphology and habitat use. We evaluated two aspects of territoriality: behavioral defense of space via territorial displays, and territory overlap within and between sexes. Controlling for the phylogenetic relationships of the taxa in our study, we found that species similar in perch height and diameter convergently evolved patterns of territory overlap, whereas species similar in habitat visibility (the proportion of space that can be seen from a perch) convergently evolved display behavior. We also found that species with greater display time have more extensive male–male territory overlap. This study provides strong evidence for the role of habitat in the evolution of territoriality and suggests that the social structure of a species ultimately evolves in concert with habitat use and morphology.     

A multi-gene phylogeny of Cephalopoda supports convergent morphological evolution in association with multiple habitat shifts in the marine environment

ABSTRACT: BACKGROUND: The marine environment is comprised of numerous divergent organisms living under similar selective pressures, often resulting in the evolution of convergent structures such as the fusiform body shape of pelagic squids, fishes, and some marine mammals. However, little is known about the frequency of, and circumstances leading to, convergent evolution in the open ocean. Here, we present a comparative study of the molluscan class Cephalopoda, a marine group known to occupy habitats from the intertidal to the deep sea. Several lineages bear features that may coincide with a benthic or pelagic existence, making this a valuable group for testing hypotheses of correlated evolution. To test for convergence and correlation, we generate the most taxonomically comprehensive multi-gene phylogeny of cephalopods to date. We then create a character matrix of habitat type and morphological characters, which we use to infer ancestral character states and test for correlation between habitat and morphology. RESULTS: Our study utilizes a taxonomically well-sampled phylogeny to show convergent evolution in all six morphological characters we analyzed. Three of these characters also correlate with habitat. The presence of an autogenic photophore is correlated with a pelagic habitat, while the cornea and accessory nidamental gland correlate with a benthic lifestyle. Here, we present the first statistical tests for correlation between convergent traits and habitat in cephalopods to better understand the evolutionary history of characters that are adaptive in benthic or pelagic environments, respectively. DISCUSSION: Our study supports the hypothesis that habitat has influenced convergent evolution in the marine environment: benthic organisms tend to exhibit similar characteristics that confer protection from invasion by other benthic taxa, while pelagic organisms possess features that facilitate crypsis and communication in an environment lacking physical refuges. Features that have originated multiple times in distantly related lineages are likely adaptive for the organisms inhabiting a particular environment: studying the frequency and evolutionary history of such convergent characters can increase understanding of the underlying forces driving ecological and evolutionary transitions in the marine environment.     

Trophic divergence despite morphological convergence in a continental radiation of snakes

Ecological and phenotypic convergence is a potential outcome of adaptive radiation in response to ecological opportunity. However, a number of factors may limit convergence during evolutionary radiations, including interregional differences in biogeographic history and clade-specific constraints on form and function. Here, we demonstrate that a single clade of terrestrial snakes from Australia—the oxyuranine elapids—exhibits widespread morphological convergence with a phylogenetically diverse and distantly related assemblage of snakes from North America. Australian elapids have evolved nearly the full spectrum of phenotypic modalities that occurs among North American snakes. Much of the convergence appears to involve the recurrent evolution of stereotyped morphologies associated with foraging mode, locomotion and habitat use. By contrast, analysis of snake diets indicates striking divergence in feeding ecology between these faunas, partially reflecting regional differences in ecological allometry between Australia and North America. Widespread phenotypic convergence with the North American snake fauna coupled with divergence in feeding ecology are clear examples of how independent continental radiations may converge along some ecological axes yet differ profoundly along others.     

Spring and autumn habitat preferences of active European hares (Lepus europaeus) in an agricultural area with low hare density

The number of European brown hares (Lepus europaeus) has been declining throughout much of Europe since the 1960s. Consequently, many studies have focused on analysing habitat selection of European hares in order to improve the suitability of the habitat for this species. Habitat preferences of European hares are known to be affected by hare density, but most studies have been conducted in agricultural areas where hare densities were medium to high. Finding habitat preferences at high densities is difficult as most available habitats are occupied. In addition, in agricultural areas, field size might influence the hares’ habitat selection because it affects the distribution and availability of certain habitat types. However, most studies relate to areas with large field sizes. In this study, we analysed the habitat preferences of European hares in spring and autumn during the activity period, in the early hours of the night, in an agricultural area with low hare density and small average field size using Chesson’s electivity index. Moreover, we focused on the question whether two different habitat classifications varying in their specificity might cause contradictory results regarding European hares’ habitat preferences. Our results show that in this agricultural area with low hare density, European hares avoided several habitat types which were preferred in other study areas with higher hare densities. Therefore, we assume that hare density has an influence on the species’ habitat selection. In contrast, the small average field size of our study area seemed not to have an effect on hare habitat preference. Furthermore, by pooling habitat types into broader groups, substantial information was lost in some categories. Hence, for some categories, e.g. grassland or agricultural crop land, more detail might be needed than for others, such as urban areas, when analysing hares’ habitat selection. In conclusion, our results imply that studies on habitat preferences have to be conducted in areas with low hare density to be able to gain knowledge on the species’ habitat requirement and hereinafter improve the suitability of the habitat for this species.     

Community convergence in bird song

Species in similar habitats are often similar in morphology or behaviour, attributed to adaptation to similar environmental selection pressures, sometimes mediated by competitive interactions. For passerine songs, similarity of phenotype in identical habitats and character displacement have been documented, the former due to adaptation to the acoustics of the habitat, and the latter due to competition for acoustic space among species. If these phenomena are widespread, they should lead to community convergence of bird songs. Here, we test if passerine communities in similar habitats converge in song attributes or in acoustic differentiation among species. We compared the songs of European and North American Mediterranean climate passerine communities in open and closed habitats. Song frequency varied across different habitats but not continents. This was independent of both phylogeny and body size, indicating community convergence due to acoustic adaptation, rather than species sorting or similarity as a by-product of another type of ecological convergence. We found little evidence for regular spacing in song features among species, as would be expected if acoustic competition shapes within-community structure. However, for one of five song components, the open habitat communities showed a similar distribution of phenotypes on each continent. The proportion of interspecific variation in song explained by these effects was small. The fact that songs are complex signals that vary in many dimensions may explain why competition for acoustic space seems to be of small importance in structuring songs in these passerine communities.     

Diverge or merge? The effect of sympatric occurrence on the territorial vocalizations of the vinaceous dove Streptopelia vinacea and the ring‐necked dove S. capicola

Sympatric occurrence of two closely related species is expected to lead to diverging or converging shifts in signal characteristics of one or both species. We examined signal characteristics in the vinaceous dove Streptopelia vinacea and the ring-necked dove S. capicola , two sister species that are mainly allopatric but occur in sympatry in northwestern Uganda. Vocal characteristics of the birds in sympatry were compared with those of an adjacent and a distant allopatric population of each species. The sympatric population showed intermediate values between the allopatric populations from Uganda. However, within each species there is little geographic variation between distant allopatric populations. Since vocal differences between dove species have a genetic base, the convergence in vocal characteristics is most likely explained by hybridization. Probably, the two species came into secondary contact relatively recently. Climatic changes during the last several thousand years and recent habitat changes caused by the growing human population, may have allowed Streptopelia capicola to extend its range in the northern direction.     

Interspecific interactions drive cultural co-evolution and acoustic convergence in syntopic species

1.?Antagonistic interactions have been favourite subjects of studies on species co-evolution, because coexistence among competing species often results in quantifiable character displacement. A common output for competitive interactions is trait divergence, although the opposite phenomenon, convergence, has been proposed to evolve in some instances, for example in the communication behaviour of species that maintain mutually exclusive territories. 2.?I use here experimental and observational evidence to study how species interactions drive heterospecific signal convergence and analyse how convergence feeds back to the interaction itself, in the form of aggressive behaviour. I recorded the learned territorial signals of two non-hybridizing larks, Galerida cristata and G.?theklae, and used allopatric populations as controls for evaluating acoustic convergence in syntopy. Acoustic variation was analysed with respect to social conditions controlling for other potential agents of natural selection, habitat and climate. 3.?Interspecific convergence of Galerida calls peaked in syntopy. Although call acoustic structure was affected by climate and habitat, it matched gradients of density and proximity to congeners even at small local scales. The process of cultural transmission, in which individuals may acquire components of behaviour by copying neighbours, enhances the correlation between call acoustics and the local social milieu. 4.?Territories were defended against both species, but playback stimuli of convergent congener calls elicited a stronger aggressive reaction than congener calls from allopatric locations. 5.?This study shows that learned behaviours may co-evolve as a consequence of antagonistic interactions, determining reciprocal cultural evolution or cultural co-evolution. As for (biological) co-evolution, the distribution of competing species influences whether a particular area becomes a syntopic environment in which convergence is occurring, or an allopatric environment lacking interactions and reciprocal change. Because of their plastic nature, cultural coadaptations may rapidly shift in response to fluctuating social selection, thus propelling dynamic interactions and fine adjustments to the local environment.     

浙江景宁畲族自治县石松类和蕨类植物区系研究

在野外调查的基础上,初步探讨了景宁畲族自治县石松类和蕨类植物的区系特征、地理分布、生态环境以及与邻近地区的关系和物种濒危状况。结果表明,景宁石松类和蕨类共有296种7变种和1杂交种,隶属于29科83属,其中包括7个浙江省新记录种;地理分布以热带性质的科属占优势,种类以温带性质为主,本区属于亚热带与温带物种的融汇地带;与邻近省份和地区相比,景宁石松类和蕨类区系与江西省、福建省、宁波市和温州市的关系密切,与温州的区系最紧密,与安徽的区系较疏远;景宁石松类和蕨类生态类型大致可分为六类:暖性针叶林生境、常绿阔叶林阴湿生境、毛竹林暖湿生境、温性松杉柏冷湿生境、灌丛及村旁路边干旱生境和溪流、农田、沼泽湿地生境,其中常绿阔叶林阴湿生境下物种最丰富;景宁分布着在浙江范围内受威胁的蕨类46种,其中濒危(EN)有11种,易危(VU)有35种,国家和浙江省保护蕨类4种。     

Comparison of the two rupicolous nightjars: the Afrotropical Freckled Nightjar Caprimulgus tristigma and the Neotropical Blackish Nightjar C. nigrescens

The Freckled Nightjar Caprimulgus tristigma and the Blackish Nightjar C. nigrescens are widespread and common within their rupicolous habitat, in the Afrotropics and Neotropics respectively, and may therefore be considered as successful in their adaptation to this habitat, a niche that has not been exploited by any other nightjar species. However, apart from a plumage pattern that matches a rocky substrate, their known life histories provide no common factors to explain this adaptive success. The factors that they do share are common to most other nightjars. While they nest and roost on rocks, their breeding biology is remarkably different. The contrasts and lack of convergence are surprising, and suggest that these two species are not as closely related as their current congeneric status implies. This is supported by recent molecular studies that place the African and South American Caprimulgus species in different well-supported clades.     

Comparison of responses to alarm calls by patas (Erythrocebus patas) and vervet (Cercopithecus aethiops) monkeys in relation to habitat structure

We studied responses to alarm calls of sympatric patas (Erythrocebus patas) and vervet (Cercopithecus aethiops) monkeys in relation to habitat structure, with the intention of understanding the relationship between the environment and predator avoidance. Patas and vervet monkeys are phylogenetically closely related and overlap in body size. However, while patas monkeys are restricted to nonriverine habitats at our study site, vervets use both nonriverine and riverine habitats, allowing us to "vary" habitat structure while controlling for effects of group size, composition, and phylogeny. Patas monkeys in the nonriverine habitat responded to mammalian predator alarm calls with a greater variety of responses than did vervets in the riverine habitat, but not when compared with vervets in the nonriverine habitat. Ecological measurements confirm subjective assessments that trees in the riverine habitat are significantly taller and occur at lower densities than trees in the nonriverine habitat. Despite the lower density of trees in the riverine habitat, locomotor behavior of focal animals indicates that canopy cover is significantly greater in the riverine than the nonriverine habitat. Differences in responses to alarm calls by the same groups of vervets in different habitat types, and convergence of vervets with patas in the same habitat type, suggest that habitat type can be a significant source of variation in antipredator behavior of primates.