Fundamental Niche Breadth Research Articles

Comparative phylogeography reveals dissimilar genetic differentiation patterns in two sympatric amphibian species.

Global climate change is expected to have a profound effect on species distribution. Due to the temperature constraints, some narrow niche species could shift their narrow range to higher altitudes or latitudes. In this study, we explored the correlation between species traits, genetic structure, and geographical range size. More specifically, we analyzed how these variables are affected by differences in fundamental niche breadth or dispersal ability in the members of two sympatrically distributed stream-dwelling amphibian species (frog, Quasipaa yei; salamander, Pachyhynobius shangchengensis), in Dabie Mountains, East China. Both species showed relatively high genetic diversity in most geographical populations and similar genetic diversity patterns (JTX, low; BYM, high) correlation with habitat changes and population demography. Multiple clustering analyses were used to disclose differentiation among the geographical populations of these two amphibian species. Q. yei disclosed the relatively shallow genetic differentiation, while P. shangchengensis showed an opposite pattern. Under different historical climatic conditions, all ecological niche modeling disclosed a larger suitable habitat area for Q. yei than for P. shangchengensis; these results indicated a wider environment tolerance or wider niche width of Q. yei than P. shangchengensis. Our findings suggest that the synergistic effects of environmental niche variation and dispersal ability may help shape genetic structure across geographical topology, particularly for species with extremely narrow distribution.

Rapid niche shifts in bacteria following conditioning in novel soil environments

Abstract Realized niche breadth is generally expected to be smaller than fundamental niche breadth. For soil microorganisms, this is due in part to competition from co‐occurring microbes, so removing competitors should allow for expanded use of resource and habitats (i.e. ecological release). We hypothesized that conditioning bacterial isolates to biotically cleared soils would allow for niche breadth expansion relative to ancestral bacteria, and that this niche expansion would be driven by habitat‐dependent niche shifts between derived populations. We grew two taxonomically divergent bacteria for 3 months in four biotically cleared soils and a biotically cleared ‘home’ soil. We then assessed changes in the niche breadth and fitness (i.e. growth; respiration; carbon resource use) of conditioned bacteria. Post‐conditioning, Pseudomonas populations showed the potential for increased growth rate in‐culture and in‐soil when conditioned to soils, and constrained resource use relative to the ancestral population, while Paenibacillus showed minimal changes in soil habitat breadth, but expanded resource use in conditioned populations. When introduced into complex novel environments containing reduced biotic pressure, soil bacteria can undergo rapid niche shifts, but this response varies across taxa and habitats. This suggests that species identity and habitat should interact to shape near‐term niche shifts when microbes establish in new soil environments. Read the free Plain Language Summary for this article on the Journal blog.

Geometry and evolution of the ecological niche in plant-associated microbes

The ecological niche can be thought of as a volume in multidimensional space, where each dimension describes an abiotic condition or biotic resource required by a species. The shape, size, and evolution of this volume strongly determine interactions among species and influence their current and potential geographical distributions, but the geometry of niches is poorly understood. Here, we analyse temperature response functions and host plant ranges for hundreds of potentially destructive plant-associated fungi and oomycetes. We demonstrate that niche specialization is uncorrelated on abiotic (i.e. temperature response) and biotic (i.e. host range) axes, that host interactions restrict fundamental niche breadth to form the realized niche, and that both abiotic and biotic niches show limited phylogenetic constraint. The ecological terms ‘generalist’ and ‘specialist’ therefore do not apply to these microbes, as specialization evolves independently on different niche axes. This adaptability makes plant pathogens a formidable threat to agriculture and forestry.

Niche syndromes reveal climate-driven extinction threat to island endemic conifers

Anthropogenic climate change is predicted to cause many extinctions worldwide1. Although species endemic to islands or archipelagos have high conservation value and are vulnerable to human impacts2,3, there has been no global analysis of climate-driven extinction risk focused on island endemics. Here, we use conifers as a model system to assess extinction risk among island endemics under climate projections for 2070. We employ the emerging technique of combining native and non-native occurrence data to model climatic conditions under which each species can sustain a population4–7 and also incorporate horticultural data to model the broader range of conditions that allow short-term survival. Our projections indicate that some species will retain suitable climatic conditions, some will experience conditions completely precluding survival and others will experience intermediate-risk conditions that lead to population decline and eventual extinction. Based on different climate change models, we report island size thresholds of 400 to 20,000 km2, below which extinction risks increase. These patterns are driven by correlations among island area and the breadth of species’ realized, fundamental and tolerance niches. Notably, realized and fundamental niche breadth are positively correlated. Our results highlight management interventions needed to protect species from climate-driven extinction across islands of different sizes. Island species are at risk as the climate changes. Island conifers are used as a model species and a combination of native and non-native occurrence data allows identification of realized, tolerable and fundamental niches; linking to island size provides an estimate of extinction risk.

Using nutritional geometry to define the fundamental macronutrient niche of the widespread invasive ant Monomorium pharaonis.

The emerging field of nutritional geometry (NG) provides powerful new approaches to test whether and how organisms prioritize specific nutritional blends when consuming chemically complex foods. NG approaches can thus help move beyond food-level estimates of diet breadth to predict invasive success, for instance by revealing narrow nutritional niches if broad diets are actually composed of nutritionally similar foods. We used two NG paradigms to provide different, but complementary insights into nutrient regulation strategies and test a hypothesis of extreme nutritional generalism in colony propagules of the globally distributed invasive ant Monomorium pharaonis. First, in two dimensions (protein:carbohydrates; P:C), M. pharaonis colonies consistently defended a slightly carbohydrate-biased intake target, while using a generalist equal-distance strategy of collectively overharvesting both protein and carbohydrates to reach this target when confined to imbalanced P:C diets. Second, a recently developed right-angled mixture triangle method enabled us to define the fundamental niche breadth in three dimensions (protein:carbohydrates:lipid, P:C:L). We found that colonies navigated the P:C:L landscape, in part, to mediate a tradeoff between worker survival (maximized on high-carbohydrate diets) and brood production (maximized on high-protein diets). Colonies further appeared unable to avoid this tradeoff by consuming extra lipids when the other nutrients were limiting. Colonies also did not rely on nutrient regulation inside their nests, as they did not hoard or scatter fractions of harvested diets to adjust the nutritional blends they consumed. These complementary NG approaches highlight that even the most successful invasive species with broad fundamental macronutrient niches must navigate complex multidimensional nutritional landscapes to acquire limiting macronutrients and overcome developmental constraints as small propagules.

Fundamental and realized feeding niche breadths of sexual and asexual stick insects.

The factors contributing to the maintenance of sex over asexuality in natural populations remain unclear. Ecological divergences between sexual and asexual lineages could help to maintain reproductive polymorphisms, at least transiently, but the consequences of asexuality for the evolution of ecological niches are unknown. Here, we investigated how niche breadths change in transitions from sexual reproduction to asexuality. We used host plant ranges as a proxy to compare the realized feeding niche breadths of five independently derived asexual Timema stick insect species and their sexual relatives at both the species and population levels. Asexual species had systematically narrower realized niches than sexual species, though this pattern was not apparent at the population level. To investigate how the narrower realized niches of asexual species arise, we performed feeding experiments to estimate fundamental niche breadths but found no systematic differences between reproductive modes. The narrow realized niches found in asexual species are therefore probably a consequence of biotic interactions such as predation or competition, that constrain realized niche size in asexuals more strongly than in sexuals.

Contrasting environments shape thermal physiology across the spatial range of the sandhopper Talorchestia capensis.

Integrating thermal physiology and species range extent can contribute to a better understanding of the likely effects of climate change on natural populations. Generally, broadly distributed species show variation in thermal physiology between populations. Within their distributional ranges, populations at the edges are assumed to experience more challenging environments than central populations (fundamental niche breadth hypothesis). We have investigated differences in thermal tolerance and thermal sensitivity under increasing/decreasing temperatures among geographically separated populations of the sandhopper Talorchestia capensis along the South African coasts. We tested whether the thermal tolerance and thermal sensitivity of T. capensis differ between central and marginal populations using a non-parametric constraint space analysis. We linked thermal sensitivity to environmental history by using historical climatic data to evaluate whether individual responses to temperature could be related to natural long-term fluctuations in air temperatures. Our results demonstrate that there were significant differences in the thermal response of T. capensis populations to both increasing/decreasing temperatures. Thermal sensitivity (for increasing temperatures only) was negatively related to temperature variability and positively related to temperature predictability. Two different models fitted the geographical distribution of thermal sensitivity and thermal tolerance. Our results confirm that widespread species show differences in physiology among populations by providing evidence of contrasting thermal responses in individuals subject to different environmental conditions at the limits of the species' spatial range. When considering the complex interactions between individual physiology and species ranges, it is not sufficient to consider mean environmental temperatures, or even temperature variability; the predictability of that variability may be critical.

A stochastic biodiversity model with overlapping niche structure

The niche is a fundamental ecological concept that underpins many explanations of patterns of biodiversity. The complexity of niche processes in ecological systems, however, means that it is difficult to capture them accurately in theoretical models of community assembly. In this study, we build upon simple neutral biodiversity models by adding the important ingredient of overlapping niche structure. Our model is spatially implicit and contains a fixed number of equal-sized habitats. Each species in the metacommunity arises through a speciation event; at which time, it is randomly assigned a fundamental niche or set of environments/habitats in which it can persist. Within each habitat, species compete with other species that have different but overlapping fundamental niches. Species abundances then change through ecological drift; each, however, is constrained by its maximum niche breadth and by the presence of other species in its habitats. Using our model, we derive analytical expressions for steady-state species abundance distributions, steady-state distributions of niche breadth across individuals and across species, and dynamic distributions of niche breadth across species. With this framework, we identify the conditions that produce the log-series species abundance distribution familiar from neutral models. We then identify how overlapping niche structure can lead to other species abundance distributions and, in particular, ask whether these new distributions differ significantly from species abundance distributions predicted by non-overlapping niche models. Finally, we extend our analysis to consider additional distributions associated with realized niche breadths. Overall, our results show that models with overlapping niches can exhibit behavior similar to neutral models, with the caveat that species with narrow fundamental niche breadths will be very rare. If narrow-niche species are common, it must be because they are in a non-overlapping niche or have countervailing advantages over broad-niche species. This result highlights the role that niches can play in establishing demographic neutrality.

Migration and niche partitioning simultaneously increase species richness and rarity

To understand species abundance distributions effectively, it is essential to consider the forces which create the overwhelmingly long ‘tail’ of rare species. Both neutral and niche theory have been invoked to explain the rarity of certain species in ecological assemblages: niche theory stresses the importance of the resource division process, while neutral theory focuses on stochastic drift in densities of competitively identical species. Here, we show how migration and niche partitioning can act simultaneously to increase both the number of rare species and the total species richness. By simulating the dynamics of a metacommunity using an interconnected network of local communities, we incorporate niche partitioning into the otherwise per capita equivalent processes of birth and death. Niche partitioning is defined by the species niche fitness function, which is measured by the species optimal environmental conditions, the fundamental niche breadths of each species, and by the breadth of the environmental gradient of each local community. For a given niche breadth at the local community scale, unimodal relationships appear between the rate of migration, the number of rare species, and the total species richness. At the metacommunity scale, species richness was at first unaffected by increasing migration, but then crashed. At wide niche breadth, both the number of rare species and the total number of species started to decline at a low rate of migration. In contrast, when niche breadth was narrow, neither the number of rare species nor the total number of species started to decline until migration rates were much higher. This is because, for a given migration rate, niche breadth can affect the proportions of individuals coming from adjacent local communities. The integration of niche partitioning and migration therefore provides a rational explanation for the widespread rarity of species in ecological communities.

Dispersal ability rather than ecological tolerance drives differences in range size between lentic and lotic water beetles (Coleoptera: Hydrophilidae)

AbstractAim In aquatic ecosystems, standing (lentic) and running (lotic) waters differ fundamentally in their stability and persistence, shaping the comparative population genetic structure, geographical range size and speciation rates of lentic versus lotic lineages. While the drivers of this pattern remain incompletely understood, the suite of traits making up the ability of a species to establish new populations is instrumental in determining such differences. Here we explore the degree to which the association between habitat type and geographical range size results from differences in dispersal ability or fundamental niche breadth in the members of theEnochrus bicolorcomplex, an aquatic beetle clade with species across the lentic–lotic divide.Location Western Mediterranean, with a special focus on North Africa, the Iberian Peninsula and Sicily.Methods DNA sequences for four loci were obtained from species of theE. bicolorcomplex and analysed using phylogenetic inference. Dispersal and establishment abilities were assessed in lentic–lotic species pairs of the complex, using flight wing morphometrics and thermal tolerance ranges as surrogates, respectively.Results There were clear differences in range size between the lotic and lentic taxa of the complex, which appears to have had a lotic origin with two transitions to standing waters. Only small differences were observed in temperature tolerance and acclimation ability between the two lotic–lentic sister species studied. By contrast, wing morphometrics revealed clear, consistent differences between lotic and lenticEnochrusspecies pairs, the latter having a higher dispersal capacity.Main conclusions We hypothesize that there have been two habitat shifts from lotic to lentic waters, which have allowed marked expansions in geographical range size in western Mediterranean species of theE. bicolorcomplex. Differences in dispersal rather than in establishment ability appear to underlie differences in geographical range extent, as transitions to lentic waters were associated with changes in wing morphology, but not in thermal tolerance range. In this lineage of water beetles, selection for dispersal in geologically short‐lived lentic systems has driven the evolution of larger range sizes in lentic taxa compared with those of their lotic relatives.

What determines a species’ geographical range? Thermal biology and latitudinal range size relationships in European diving beetles (Coleoptera: Dytiscidae)

1. The geographical range sizes of individual species vary considerably in extent, although the factors underlying this variation remain poorly understood, and could include a number of ecological and evolutionary processes. A favoured explanation for range size variation is that this result from differences in fundamental niche breadths, suggesting a key role for physiology in determining range size, although to date empirical tests of these ideas remain limited. 2. Here we explore relationships between thermal physiology and biogeography, whilst controlling for possible differences in dispersal ability and phylogenetic relatedness, across 14 ecologically similar congeners which differ in geographical range extent; European diving beetles of the genus Deronectes Sharp (Coleoptera, Dytiscidae). Absolute upper and lower temperature tolerance and acclimatory abilities are determined for populations of each species, following acclimation in the laboratory. 3. Absolute thermal tolerance range is the best predictor of both species' latitudinal range extent and position, differences in dispersal ability (based on wing size) apparently being less important in this group. In addition, species' northern and southern range limits are related to their tolerance of low and high temperatures respectively. In all cases, absolute temperature tolerances, rather than acclimatory abilities are the best predictors of range parameters, whilst the use of independent contrasts suggested that species' thermal acclimation abilities may also relate to biogeography, although increased acclimatory ability does not appear to be associated with increased range size. 4. Our study is the first to provide empirical support for a relationship between thermal physiology and range size variation in widespread and restricted species, conducted using the same experimental design, within a phylogenetically and ecologically controlled framework.

Range size, dispersal and niche breadth in the herbaceous flora of central England

1It has been suggested that rare species differ from related common species in a variety of traits, including (among others) niche breadth and dispersal ability. We set out to test these ideas in the flora of central England.2We used two measures of range: number of hectads in Britain (national range) and number of 1 km2in a 3000‐km2area of central England (local range). In each case we regressed phylogenetically independent contrasts in geographical range against contrasts in range of germination temperature (one aspect of fundamental niche breadth), terminal velocity of dispersule (a measure of wind dispersal capacity), seed weight and specialism index (a measure of the diversity of habitats exploited in central England). Seed weights and germination temperature were known for 263 species, specialism index for 261 and terminal velocity for 178.3Specialism index explained by far the largest part of the variance in local and national range. Seed weight, terminal velocity and germination temperature each explained only 2–4% of the variation in local range, and none of the variation in national range.4Most previous attempts to relate niche breadth and dispersal ability to range have concerned animals. There is little convincing published evidence for plants, and in the British herbaceous seed plants studied here the best predictor of range was diversity of habitats exploited. This pattern was independent of phylogeny.

A Competitive Hierarchy Model Integrating Roles of Physiological Competence and Competitive Ability Does Not Provide a Mechanistic Explanation for the Zonation of Three Intertidal Fucus Species in Europe

It has been clear for the last 20 yr that both competitive ability and physiological competence on the intertidal gradient of rocky shores determine the zoned distribution of fucoid seaweeds in the North Atlantic. However to this point, there has been no concept integrating these functions for seaweed vegetation in a single mechanistic explanation. Keddy's competitive hierarchy model, which has not been tested in marine systems (i.e. not on seaweed vegetation) provides an explanation for the zonation of plant species on environmental gradients. The model proposes that competitive abilities of species on a stress or resource gradient are inversely related to fundamental niche breadths. We tested 2 assumptions of the model to determine whether it provided a comprehensive explanation of zonation of 3 Fucus species on the island of Helgoland in the North Sea. The 2 assumptions translate into specific predictions for the Fucus assemblage (where F. serratus occurs on the low shore, F. spiralis on the high shore, and F. vesiculosus in between): I. competitive ranking is F. serratus > F. vesiculosus > F. spiralis; 2. fundamental niche breadth rankings are the reverse of competitive ability rankings. Pairwise competition experiments were done in the field. A highly modified substitutive design was used, in order to take into account the shortcomings of this approach. The empirically derived competitive hierarchy did not fit prediction I. Transplant experiments with adults and juveniles provided results contrary to prediction 2. Since none of the assumptions of the model fit, it cannot be used to provide a mechanistic explanation for the zonation of Fucus species on Helgoland. Unlike other important models of competition, Keddy's approach does not claim universal validity in all communities. This means that it requires empirical testing in each species assemblage, and more importantly, that the negative outcome reported here does not invalidate the concept in general.