Hidden patterns of phylogenetic non‐stationarity overwhelm comparative analyses of niche conservatism and divergence

Aim Despite the importance of the niche concept in ecological and evolutionary theory, there are still many discussions about its definition and operational evaluation, especially when dealing with niche divergence and conservatism in an explicit phylogenetic context. Here we evaluate patterns of niche evolution in 67 New World Carnivora species, measured using Hellinger distances based on MAXENT models of species distribution. We show how inferences on niche conservatism or divergence depend on the way phylogenetic patterns are analysed using matrix comparison techniques. Innovation Initially we used the simplest approach of Mantel tests to compare Hellinger distances ( N ) derived from MAXENT and phylogenetic distances ( P ) among species. Then we extended the Mantel test to generate a multivariate correlogram, in which phylogenetic patterns are analysed at multiple levels in the phylogeny and can reveal nonlinearity in the relationship between divergence and time. Finally, we proposed a new approach to generate ‘local’ (or ‘specific’) leverages of components for Mantel correlation, evaluating the non‐stationarity in the relationship between N and P for each species. This new approach was used to show if some lineages are more prone to niche shift or conservatism than others. Main conclusions Standard Mantel tests indicated a poor correspondence between N and P matrices, discarding the idea of niche conservatism for Carnivora, but the correlogram supports that closely related species tend to be more similar than expected by chance. Moreover, the variance among Hellinger distances between pairs of closely phylogenetically related species is much larger than for the entire clade. Phylogenetic non‐stationarity analysis shows that in some Carnivora families the niche tends to divergence (Mustelidae and Canidae), whereas in others it tends to conservatism (Procyonidae and Mustelidae) at short phylogenetic distances. Our analyses clearly show that misleading results may appear if niche divergence is analysed only by simple matrix correlations not taking into account complex patterns of phylogenetic nonlinearity and non‐stationarity.     

Biogeography of the Amazon molly: ecological niche and range limits of an asexual hybrid species

Aim To understand the relative contributions of environmental factors, dispersal limitations and the presence of sperm donors in determining the distribution of the Amazon molly (Poecilia formosa), a sperm‐dependent unisexual fish species of hybrid origin. To explore niche similarities and/or differences between the hybrid and parental species. To evaluate whether large‐scale abiotic factors can explain a successful introduction of both P. formosa and Poecilia latipinna. Location South‐east United States, Mexico and Central America. Methods We used abiotic variables in ecological niche modelling (ENM) to identify regions with suitable conditions for the presence of the Amazon molly and its two parental species (P. latipinna and Poecilia mexicana). We also used a recently developed metric to calculate the degree of niche overlap between the hybrid and its parental species. Results ENM produced highly significant models [all area under the curve (AUC) > 0.99 for the three species]. Annual mean temperature and minimum temperature of the coldest month were the variables that best explained the distribution of the Amazon molly. With the exception of south Florida, few areas beyond the known distribution of the species were predicted to have suitable environmental conditions. The hybrid species niche overlaps partially with the parental species. However, given the available data, it is neither more similar nor more different than expected by chance. Main conclusions Two different processes are acting to limit the distribution of P. formosa. At the northern limit, although a sperm donor species is present further north, suitable environmental conditions are absent from nearby locations. At the southern limit, a sperm donor species is present and areas with good environmental conditions are present at nearby locations, suggesting that dispersal ability is the limiting factor. We found that the hybrid species overlaps in a similar way with both parental species while still having its own niche identity. This result may be explained by the fact that hybrid species inherit characteristics of two ecologically divergent species, which can result in intermediate or even transgressive phenotypes. These results support recent work on the role of hybridization in diversification.     

Rivers as islands: determinants of the distribution of Andean astroblepid catfishes

The distribution of astroblepids was examined using predictive niche modelling techniques to explore the physical and environmental factors responsible for determining the limits to their geographic distribution in the tropical Andes. Astroblepids occur in streams across a wide range of elevations (100-4600 m) and ecosystems from Panama to Bolivia, with most occurrences between 500 and 2000 m and associated with a narrow range of mean temperatures (17-24° C). The Maxent-predicted distribution was 83% accurate, statistically significant (AUC = 0·965), and closely matched the known distribution, with few notable exceptions. Four environmental variables contributed a cumulative 84% to the prediction, with elevation the most important, followed by temperature seasonality, isothermality and maximum temperature of the warmest month. The greatest discrepancy between the predicted and known distributions involved areas of predicted habitat suitability where there are no associated occurrence records. A jackknife test of variable contribution to the model showed that elevation contributed to the predicted distribution in ways not simply accounted for by temperature. Contrary to expectations, land cover type and vegetation characteristics contributed relatively little to the model prediction.     

Occurrence and dominance of six Pacific Northwest conifer species

Questions: Can probability of occurrence and dominance be accurately estimated for six important conifer species with varying range sizes? Does range size impact the accuracy of species probability of occurrence models? Is species predicted probability of occurrence significantly related to observed dominance? Location: Pacific Northwest region, North America (60°–40°N, 140°–110°W). Methods: This study develops near range‐wide predictive distribution maps for six important conifer species (Pseudotsuga menziesii, Tsuga heterophylla, Pinus contorta, Thuja plicata, Larix occidentalis, and Picea glauca) using forest inventory data collected across the United States and Canada. Species model accuracies are compared with range size using a rank scoring system. A suite of climate and topographic predictor variables are used to investigate environmental constraints that limit species range and quantify relationships between species predicted probability of occurrence and dominance at both plot and landscape scales. Results: Evaluation statistics revealed significant and accurate probability of occurrence models were developed for all six species. Based on ranked evaluation statistics, Tsuga heterophylla had highest overall model accuracy (statistic rank score=5) and Pinus contorta the lowest (statistic rank score=17). Across species, ranked evaluation statistics also revealed a pattern of decreasing model accuracy with increasing range size. At plot level, correlations between dominance and probability of occurrence were weakly positive for all species with only half of the species having statistically significant correlations. Pseudotsuga menziesii had the highest correlation (r=0.36, P<0.001) and Thuja plicata lowest (r=0.038, P=0.799). At the 50‐km scale, correlations between dominance and probability of occurrence improved for all species except Pinus contorta. Pseudotsuga menziesii displayed the highest correlation (r=0.68, P<0.001) and Thuja plicata the lowest (r=0.07, P>0.709). Conclusions: Species probability of occurrence model accuracy decreased with increasing range size. The strength and significance of correlations between probability of occurrence and dominance varied considerably by species and across spatial scales. Apart from Pseudotsuga menziesii and L. occidentalis, the results suggest that probability of occurrence is not a consistently reliable surrogate for species dominance in Pacific Northwest forests. We demonstrate how the degree of correlation between species occurrence and dominance can be used as an indicator of how well predictions of occurrence characterize the optimal niche of a species.     

太行山中段植物群落优势种生态位研究

运用TWINSPAN把样方分为8个群落类型,用Levins、Shannon-wiener生态位宽度公式和Petraitis生态位特定重叠指数公式测定群落中主要种群生态位宽度和生态位重叠,并分析各种群生态位的生态学意义。在总群落中,披针苔草和草地早熟禾的生态位宽度最大,说明它们对群落环境的适应能力最强,对资源的利用能力也最强;在不同的群落里（群落Ⅰ到群落Ⅷ）,相同种群生态位宽度有极大差别,草地早熟禾在群落Ⅱ中,B1为 2.753,B2为 15.561,在群落Ⅷ中,B1为0,B2为1;总群落中,各种群的生态位宽度明显大于其在其他群落里的生态位宽度。两个种群的生态位重叠值越大,说明它们占据越相似的资源空间,珠芽蓼和火绒草的生态位重叠值高达0.892（群落Ⅰ中）,说明它们利用资源的相似性程度很高;在总群落中,各种群之间生态位重叠值都很低。     

山西绵山植被优势种群生态位研究

应用Shannon-Weaver指数和Portraitis方法,研究了山西绵山植被优势种群的生态位宽度、生态位普遍重叠和特定重叠,结果表明：(1)乔木层中辽东栎生态位宽度最大（2.458 7）;灌木层中山桃（2.342 2）和土庄绣线菊（2.306 1）生态位宽度最大;草本层中披针苔草（2.518 7）和山蒿（2.218 2）生态位宽度最大。这主要由于这些物种的生态幅较宽,是绵山植被的主要建群种或优势种,对环境具有广泛的适应性;(2)群落中25个优势种群之间并不存在完全的普遍重叠,说明这些植物各自具有不尽相同的生物学特性及生态适应性;(3)乔木层物种除辽东栎与其它植物间具有一定的重叠之外,其它乔木间生态位重叠较少;灌木层中六道木与土庄绣线菊生态位重叠值最大（0.663）,其次是山桃和胡枝子（0.587）;草本植物中披针苔草与糙苏（0.339）、铁杆蒿与山蒿（0.245）表现出较大的特定重叠。种对间生态位重叠值越大,表明它们彼此间具有较为相似的生物学特性和生态适应性,反之亦然。如六道木与土庄绣线菊、披针苔草与糙苏,它们均为耐荫植物,具有一定程度的耐荫性;而山桃和胡枝子、山蒿与铁杆蒿则为喜阳耐旱植物。     

Reconciling niche and neutrality: the continuum hypothesis

In this study, we ask if instead of being fundamentally opposed, niche and neutral theories could simply be located at the extremes of a continuum. First, we present a model of recruitment probabilities that combines both niche and neutral processes. From this model, we predict and test whether the relative importance of niche vs. neutral processes in controlling community dynamics will vary depending on community species richness, niche overlap and dispersal capabilities of species (both local and long distance). Results demonstrate that niche and neutrality form ends of a continuum from competitive to stochastic exclusion. In the absence of immigration, competitive exclusion tends to create a regular spacing of niches. However, immigration prevents the establishment of a limiting similarity. The equilibrium community consists of a set of complementary and redundant species, with their abundance determined, respectively, by the distribution of environmental conditions and the amount of immigration.     

Architecture,seasonal growth and interference in three grass species with different flowering phenologies in a tropical savanna

In a field experiment we studied the relationships between architecture, seasonal aerial biomass growth and interference from neighbours in three savanna grass species differing in time of flowering: a precocious species (Elyonurus adustus), an early species (Leptocoryphium lanatum) and a late species (Andropogon semiberbis). To detect the neighbour interference upon architecture and seasonal regrowth, we measured the leaf interception of a plane at different heights, when the species grew alone, in pairs and in groups of three. Although the three species differed widely in the spatial and temporal patterns of occupation of above-ground space, important levels of interference among neighbouring plants were detected. The species differ in: a) the pattern of space occupation when growing alone; b) the magnitude of the interference effect by the companion species; c) the change in pattern as a consequence of interference; d) their reaction to fire.The interference is not symmetric and it is not related to phenological similarities based on flowering season.L. lanatum was both the most impaired and the least impairing of the three species and the opposite is valid forA. semiberbis. The basal species (E. adustus andL. lanatum) showed a higher potential to produce leaf surface during the growth season than the tall species (A. semiberbis), but the stronger interference from the latter tended to equate their growth when the species grew in mixtures.In all three species interference led to a reduction of the growing period. Based on the analysis of growth at the various heights and the architectural peculiarities of the species we concluded that neighbour interference is probably reducing both tillering and leafing in the basal species but only culm elongation and leafing in the erect species.The species also differed in their reaction to fire.A. semiberbis andE. adustus showed a pulse of regrowth after the passing of fire which is missing inL. lanatum. In all cases the neighbour interference affected both the intensity of growth and the length of the growing period, but it did not affect either the height of the plants nor the reproductive phenology of these three grass species.     

The fitness cost of generalization: present limitations and future possible solutions

One of the longest and liveliest debates in the evolutionary and ecological literature has centred on the existence and magnitude of constraints that can also be described by a proverb 'jack-of-all-trades is a master of none'. Often assumed, rarely tested, this proverb/assumption states that evolution of generalization necessarily entails a cost. The cost is expressed in terms of fitness loss elsewhere along an environmental gradient that leads to a genetic fitness trade-off between a generalist and a specialist. Although there is a well-developed body of knowledge that documents the cost of adaptation in general, the genetic fitness cost of generalization remains unclear. An empirical test of such cost is not a trivial task because it requires knowledge of a genotype's fundamental ecological niche breadth to document the process of generalization. The estimation of genetic fitness correlation between environments, a commonly used method in the literature, has a limited explanatory power regarding the cost of generalization, and new approaches are needed to further clarify the existence as well as the nature/pattern of constraints in evolution of generalization and specialization. A new approach is proposed to examine experimentally the genetic fitness cost of generalization, which is based on statistical analysis of tolerance curve properties. The approach can be used to study natural populations of both unicellular and multicellular organisms.  © 2007 The Linnean Society of London, Biological Journal of the Linnean Society , 2007, 90 , 583–590.     

Group Composition, Home Range Size, and Diet of Three Sympatric Bamboo Lemur Species (Genus Hapalemur) in Ranomafana National Park, Madagascar

This is the first long-term, simultaneous, comparative study of three bamboo lemur species (Hapalemur griseus, H. aureus, and H. simus) at a site in southeastern-central Madagascar where they occur in sympatry. At Talatakely, Ranomafana National Park, the three Hapalemur spp. share overlapping home ranges. Hapalemur griseus has flexible group sizes, varying from three to nine individuals (n = 6). The home range of Hapalemur griseus averages 15 ha (n = 2). Hapalemur aureus forms family groups of 4 individuals (n = 3); they have a home range on average of 26 ha (n = 2). The single group of Hapalemur simus is composed of one or three adult males, two adult females, and their offspring; they occupy a home range of 62 ha. The three species of Hapalemur are year-round bamboo specialists: >88% of their diets consist of bamboo and grass in the Family Poaceae. Contrary to earlier findings, all three Hapalemur spp. consume the cynogenic parts—young leaf bases, young pseudopetioles, and young shoots—of the giant bamboo, Cathariostachys madagascariensis. They rely heavily on this plant, which comprises 72–95% of their diets. Hapalemur griseus and H. aureus consume similar proportions of bamboo vs. nonbamboo plants, though they differ in the species of bamboo they prefer. Hapalemur simus has the most distinct diet of the three bamboo lemurs. They exploit the young shoots of Cathariostachys madagascariensis during the austral summer rainy season, between November and April. From June to November, Hapalemur simus shifts its diet to eating the mature culm pith of Cathariostachys madagascariensis; the proportion of pith represented in their diet reaches a maximum of 89% in October. Seasonal availability of food resources, feeding competition, and factors related to body size may provide clues to the understanding of diet selection among the three sympatric Hapalemur spp.