Is the Relationship between Body Size and Trophic Niche Position Time-Invariant in a Predatory Fish? First Stable Isotope Evidence

Characterizing relationships between individual body size and trophic niche position is essential for understanding how population and food-web dynamics are mediated by size-dependent trophic interactions. However, whether (and how) intraspecific size-trophic relationships (i.e., trophic ontogeny pattern at the population level) vary with time remains poorly understood. Using archival specimens of a freshwater predatory fish Gymnogobius isaza (Tanaka 1916) from Lake Biwa, Japan, we assembled a long-term (>40 years) time-series of the size-dependence of trophic niche position by examining nitrogen stable isotope ratios (δ ¹⁵N) of the fish specimens. The size-dependence of trophic niche position was defined as the slope of the relationship between δ ¹⁵N and log body size. Our analyses showed that the slope was significantly positive in about 60% of years and null in other years, changing through time. This is the first quantitative (i.e., stable isotope) evidence of long-term variability in the size-trophic relationship in a predatory fish. This finding had implications for the fish trophic dynamics, despite that about 60% of the yearly values were not statistically different from the long-term average. We proposed hypotheses for the underlying mechanism of the time-varying size-trophic relationship.     

Niche tracking and rapid establishment of distributional equilibrium in the house sparrow show potential responsiveness of species to climate change

The ability of species to respond to novel future climates is determined in part by their physiological capacity to tolerate climate change and the degree to which they have reached and continue to maintain distributional equilibrium with the environment. While broad-scale correlative climatic measurements of a species' niche are often described as estimating the fundamental niche, it is unclear how well these occupied portions actually approximate the fundamental niche per se, versus the fundamental niche that exists in environmental space, and what fitness values bounding the niche are necessary to maintain distributional equilibrium. Here, we investigate these questions by comparing physiological and correlative estimates of the thermal niche in the introduced North American house sparrow (Passer domesticus). Our results indicate that occupied portions of the fundamental niche derived from temperature correlations closely approximate the centroid of the existing fundamental niche calculated on a fitness threshold of 50% population mortality. Using these niche measures, a 75-year time series analysis (1930-2004) further shows that: (i) existing fundamental and occupied niche centroids did not undergo directional change, (ii) interannual changes in the two niche centroids were correlated, (iii) temperatures in North America moved through niche space in a net centripetal fashion, and consequently, (iv) most areas throughout the range of the house sparrow tracked the existing fundamental niche centroid with respect to at least one temperature gradient. Following introduction to a new continent, the house sparrow rapidly tracked its thermal niche and established continent-wide distributional equilibrium with respect to major temperature gradients. These dynamics were mediated in large part by the species' broad thermal physiological tolerances, high dispersal potential, competitive advantage in human-dominated landscapes, and climatically induced changes to the realized environmental space. Such insights may be used to conceptualize mechanistic climatic niche models in birds and other taxa.     

Links between plant species’ spatial and temporal responses to a warming climate

To generate realistic projections of species’ responses to climate change, we need to understand the factors that limit their ability to respond. Although climatic niche conservatism, the maintenance of a species’s climatic niche over time, is a critical assumption in niche-based species distribution models, little is known about how universal it is and how it operates. In particular, few studies have tested the role of climatic niche conservatism via phenological changes in explaining the reported wide variance in the extent of range shifts among species. Using historical records of the phenology and spatial distribution of British plants under a warming climate, we revealed that: (i) perennial species, as well as those with weaker or lagged phenological responses to temperature, experienced a greater increase in temperature during flowering (i.e. failed to maintain climatic niche via phenological changes); (ii) species that failed to maintain climatic niche via phenological changes showed greater northward range shifts; and (iii) there was a complementary relationship between the levels of climatic niche conservatism via phenological changes and range shifts. These results indicate that even species with high climatic niche conservatism might not show range shifts as instead they track warming temperatures during flowering by advancing their phenology.     

Identifying climatic niche shifts using coarse‐grained occurrence data: a test with non‐native freshwater fish

Aim We tested whether coarse‐grained occurrence data can be used to detect climatic niche shifts between native and non‐native ranges for a set of widely introduced freshwater fishes. Location World‐wide. Methods We used a global database of freshwater fish occurrences at the river basin scale to identify native and non‐native ranges for 18 of the most widely introduced fish species. We also examined climatic conditions within each river basin using fine‐grained climate data. We combined this information to test whether climatic niche shifts have occurred between native and non‐native ranges. We defined climatic niche shifts as instances where the ranges of a climatic variable within native and non‐native basins exhibit zero overlap. Results We detected at least one climatic niche shift for each of the 18 studied species. However, we did not detect common patterns in the thermal preference or biogeographic origin of the non‐native fish, hence suggesting a species‐specific response. Main conclusions Coarse‐grained occurrence data can be used to detect climatic niche shifts. They also enable the identification of the species experiencing niche shifts, although the mechanisms responsible for these shifts (e.g. local adaptation, dispersal limitation or physiological constraints) have yet to be determined. Furthermore, the coarse‐grained approach, which highlights regions where climatic niche shifts have occurred, can be used to select specific river basins for more detailed, fine‐grained studies.     

Potential Effects of Climate Warming on Fish Habitats in Temperate Zone Lakes with Special Reference to Lake 239 of the Experimental Lakes Area (ELA), North-Western Ontario

We used simple statistics (e.g. mean temperature, degree days, cumulative volume days) to describe present thermal habitats for cool water (yellow perch, Perca flavescens) and cold water (lake trout, Salvelinus namaycush) fish of a small boreal lake. We then modelled changes in the vertical and temporal extent of these habitats under various scenarios of climatic change that included increases in air temperature of 2°C, 4°C, and 9°C, and positive and negative deviations from present levels of 10% in solar radiation and relative humidity, and 20% in wind speed and the lake water extinction coefficient. Model simulations indicated pronounced changes in the temporal and vertical availability of fish thermal niche space. These changes were mainly driven by the large increases in mean mixed layer temperatures that corresponded to 85% of the increases in air temperature, but, in particular, changes in light attenuation also resulted in some non-linear, unexpected effects in the distribution and seasonal availability of thermal niche space. As expected, classical lake trout thermal habitat (5–15°C) was progressively reduced and almost disappeared in littoral areas in spring and early summer. Perch thermal niche space expanded for air temperature increases of up to 4°C, but largely disappeared for the 9°C increase. We discuss changes in thermal habitat with regard to the life history of lake trout and yellow perch, and include other determinants of fish habitat to evaluate the potential of these species for long-term ecological success under climatic warming.     

Climatic niche breadth determines the response of bumblebees (<Emphasis Type="Italic">Bombus</Emphasis> spp.) to climate warming in mountain areas of the Northern Iberian Peninsula

Studies examining species range shifts in the face of climate change have consistently found that response patterns are complex and varied, suggesting that ecological traits might be affecting species response. However, knowledge of how the traits of a species determine its response to climate change is still poorly understood. Here we investigate the role of species-specific climate niche breadth in forecasting bumblebee (Bombus spp.) responses to regional climate warming in the Cantabrian Range (north-western Iberian Peninsula). Climate niche breadth was defined using known data for occurrences of specific species at their continental (i.e., European) scale of distribution. For each bumblebee species, climate niche breadth was found to be related to (1) the elevational range shifts of species between their historical (1988–1989) and recent (2007–2009) distribution and (2) the variation in the climatic conditions of the localities they inhabited (i.e., the local climate space) between both study periods. Our results show a strong relationship between climate niche breadth, particularly thermal niche breadth, and the response of bumblebee species to climate warming, but only when this response was determined as variations in local climate space. The main conclusions of our work are thus twofold. First, variations in the climatic conditions underlying range shifts are useful in making accurate assessments of the impact of climate change on species distributions. Second, climate niche breadth is a particularly informative ecological trait for forecasting variations in species responses to climate change.     

Niche dynamics in the European ranges of two African carnivores reflect their dispersal and demographic histories

According to recent phylogeographical evidence, the common genet (Genetta genetta) and the Egyptian mongoose (Herpestes ichneumon) have dissimilar dispersal histories from Maghreb to south‐western Europe. Through comparative ecological niche modelling based on >1100 occurrences, we assessed whether the niche dynamics (i.e. niche shift versus conservatism) of the two species in their European ranges reflected DNA‐based demographic scenarios. Sensitivity analyses and projections of climatic niche models from the species' native ranges (Africa and Middle East) to Europe yielded support for (1) partial climatic niche shift in the northern European range of the common genet and (2) climatic niche conservatism in the Egyptian mongoose. Our results were consistent with demographic scenarios that predicted multiple introductions and demographic expansion in the common genet and long‐term, stable historical demography in the Egyptian mongoose. Our models further predicted a range expansion of the common genet in north‐western France and Italy, and progression of the Egyptian mongoose into Europe from the Near East. Overall, our study suggested a scenario of different niche dynamics in Europe for these two species of African carnivores, supporting the view that historical factors such as dispersal and demographic history may shape niche dynamics and thus distribution potential in colonized ranges. © 2015 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114 , 737–751.     

Macroecological Patterns of Climatic Niche Breadth Variation in Lacertid Lizards

Measuring climatic niche position and breadth may help to determine where species can occur over space and time. Using GIS-based and phylogenetic comparative methods, we investigated global patterns of variation in climatic niche breadth in lacertid lizards to test the following three hypotheses about climatic niche widths. First, does a species' temperature or precipitation niche breadth relate to its temperature or precipitation niche position(the mean value of annual mean temperature or annual precipitation across sampled localities in the range of each species)? Second, are there trade-offs between a species' temperature niche breadth and precipitation niche breadth? Third, does a species' temperature or precipitation niche breadth relate to altitude or latitude? We expect that:(1) species distributed in cold regions are specialized for low-temperature environments(i.e. narrow niche breadth center around low temperatures);(2) a negative relationship between species niche breadth on temperature and precipitation axes according to the tradeoff hypothesis(i.e. species that tolerate a broad range of precipitation regimes cannot also tolerate a broad range of temperatures);(3) precipitation niche breadth decreases with altitude or latitude, whereas temperature climatic niche breadth increases with altitude or latitude. Based on the analytical results we found that:(1) temperature niche breadth and position are negatively related, while precipitation niche breadth and position are positively related;(2) there is no trade-off between temperature and precipitation niche breadths; and (3) temperature niche breadth and latitude/altitude are positively related, but precipitation niche breadth and latitude/altitude are not significantly related. Our results show many similarities with previous studies on climatic niche widths reported for amphibians and lizards, which provide further evidence that such macroecological patterns of variation in climatic niche breadths may be widespread.     

Predicting the impact of future climate changes and range-shifts of Indian hornbills (family: Bucerotidae)

Climate change influences species distribution and is regarded as a major threat to biodiversity. Hornbills (Family: Bucerotidae) are large tropical birds in Asia and Africa. They are seed dispersers known as forest farmers because they help maintain the ecological community structure by allowing forest regeneration. They are keystone species, and their presence in a forest implies a healthy ecosystem. Range shifts due to climate change is a serious threat because their long-term survival is already imperilled by anthropogenic disturbances. This study models the current and future potential climatic niches of eight of the nine hornbill species present in India. We used GBIF-mediated species presence records along with eight WorldClim V2.1 bioclimatic variables to model the current climatically suitable areas and projected it into the future (mid-century, i.e., 2041–60 and end of the century, i.e., 2081–2100) for different CMIP6 based Shared Socioeconomic Pathway (SSPs) (i.e., SSP126, SSP245, 370 and 585). Range shifts, centroid changes, and the impact of current land use practices for each of the eight species under various climatic conditions were also examined. The Area Under Curve (AUC) values for final models ranged between 0.736 and 0.994. Result indicates that majority of species' climatic niche shift is towards the west, followed by northwest and northern shifts. The species are expected to lose >40% of their suitable present climatic niche under the SSP 585 scenario in 2081–2100. Natural areas were found to be climatically suitable for hornbills throughout the study area, implying the merit of conserving their existing habitats. Our research provides detailed information on how the distribution of Indian Hornbills may change because of future climatic conditions. Detailed spatial and temporal distribution and range shift patterns will aid in a targeted approach for conserving hornbills and their habitat in a changing climate.     

Climate interacts with anthropogenic drivers to determine extirpation dynamics

Theoretical studies suggest that the dynamics of a species’ range during a period of climate change depends upon the existence and interplay of various ecological and evolutionary processes. Here we tested how anthropogenic pressures contribute to climate‐mediated extirpation patterns of 32 freshwater fish species over the last 20 yr. We contrasted two extreme cases to determine whether extirpations were governed by patterns of climate exposure, assuming full adaptation of species to local climate, or instead by the interplay between climate exposure and the distance from the centroid of species’ climatic niches, assuming a fixed niche, and asked whether anthropogenic disturbances interact with these climatic drivers. We found strong support for the fixed niche hypothesis, but showed that species‐specific local adaptation to climate may also be important in determining extirpation dynamics. We also demonstrated that anthropogenic disturbance acted in concert with climate, ultimately determining population changes. Our results add novel evidence that unravelling the direct links between range dynamics and climate requires a multifaceted treatment, and that accounting for the cumulative effects of anthropogenic pressures deserves special attention in the context of climate change.     

Niche width predicts extinction from climate change and vulnerability of tropical species

Climate change may be a major threat to global biodiversity, especially to tropical species. Yet, why tropical species are more vulnerable to climate change remains unclear. Tropical species are thought to have narrower physiological tolerances to temperature, and they have already experienced a higher estimated frequency of climate-related local extinctions. These two patterns suggest that tropical species are more vulnerable to climate change because they have narrower thermal niche widths. However, no studies have tested whether species with narrower climatic niche widths for temperature have experienced more local extinctions, and if these narrower niche widths can explain the higher frequency of tropical local extinctions. Here, we test these ideas using resurvey data from 538 plant and animal species from 10 studies. We found that mean niche widths among species and the extent of climate change (increase in maximum annual temperatures) together explained most variation (>75%) in the frequency of local extinction among studies. Surprisingly, neither latitude nor occurrence in the tropics alone significantly predicted local extinction among studies, but latitude and niche widths were strongly inversely related. Niche width also significantly predicted local extinction among species, as well as among and (sometimes) within studies. Overall, niche width may offer a relatively simple and accessible predictor of the vulnerability of populations to climate change. Intriguingly, niche width has the best predictive power to explain extinction from global warming when it incorporates coldest yearly temperatures.     

Long-term changes within the invertebrate and fish communities of the Upper Rhône River: effects of climatic factors

There is increasing evidence that the global climate change is already having measurable biological impacts. However, no study (based on actual data) has assessed the influence of the global warming on communities in rivers. We analyzed long‐term series of fish (1979–1999) and invertebrate (1980–1999) data from the Upper Rhône River at Bugey to test the influence of climatic warming on both communities. Between the periods of 1979–1981 and 1997–1999, the average water temperature of the Upper Rhône River at Bugey has increased by about 1.5°C due to atmospheric warming. In the same period, several dams have been built from 12.5 to 85 km upstream of our study segment and a nuclear power plant has been built on it. Changes in the community structure were summarized using multivariate analysis. The variability of fish abundance was correlated with discharge and temperature during the reproduction period (April–June): low flows and high temperatures coincided with high fish abundance. Beyond abundance patterns, southern, thermophilic fish species (e.g. chub, and barbel) as well as downstream, thermophilic invertebrate taxa (e.g. Athricops, Potamopyrgus) progressively replaced northern, cold‐water fish species (e.g. dace) and upstream, cold‐water invertebrate taxa (e.g. Chloroperla, Protoneumura). These patterns were significantly correlated with thermal variables, suggesting that shifts were the consequences of climatic warming. All analyses were carried out using statistics appropriate for autocorrelated time series. Our results were consistent with previous studies dealing with relationships between fish or invertebrates and water temperature, and with predictions of the impact of climatic change on freshwater communities. The potential confounding factors (i.e. dams and the nuclear power plant) did not seem to influence the observed trends.     

Climatic Niche Conservatism and Biogeographical Non-Equilibrium in Eschscholzia californica (Papaveraceae), an Invasive Plant in the Chilean Mediterranean Region

Species climate requirements are useful for predicting their geographic distribution. It is often assumed that the niche requirements for invasive plants are conserved during invasion, especially when the invaded regions share similar climate conditions. California and central Chile have a remarkable degree of convergence in their vegetation structure, and a similar Mediterranean climate. Such similarities make these geographic areas an interesting natural experiment for testing climatic niche dynamics and the equilibrium of invasive species in a new environment. We tested to see if the climatic niche of Eschscholzia californica is conserved in the invaded range (central Chile), and we assessed whether the invasion process has reached a biogeographical equilibrium, i.e., occupy all the suitable geographic locations that have suitable conditions under native niche requirements. We compared the climatic niche in the native and invaded ranges as well as the projected potential geographic distribution in the invaded range. In order to compare climatic niches, we conducted a Principal Component Analysis (PCA) and Species Distribution Models (SDMs), to estimate E. californica''s potential geographic distribution. We also used SDMs to predict altitudinal distribution limits in central Chile. Our results indicated that the climatic niche occupied by E. californica in the invaded range is firmly conserved, occupying a subset of the native climatic niche but leaving a substantial fraction of it unfilled. Comparisons of projected SDMs for central Chile indicate a similarity, yet the projection from native range predicted a larger geographic distribution in central Chile compared to the prediction of the model constructed for central Chile. The projected niche occupancy profile from California predicted a higher mean elevation than that projected from central Chile. We concluded that the invasion process of E. californica in central Chile is consistent with climatic niche conservatism but there is potential for further expansion in Chile.     

CLIMBER: Climatic niche characteristics of the butterflies in Europe

Detailed information on species’ ecological niche characteristics that can be related to declines and extinctions is indispensable for a better understanding of the relationship between the occurrence and performance of wild species and their environment and, moreover, for an improved assessment of the impacts of global change. Knowledge on species characteristics such as habitat requirements is already available in the ecological literature for butterflies, but information about their climatic requirements is still lacking. Here we present a unique dataset on the climatic niche characteristics of 397 European butterflies representing 91% of the European species (see Appendix). These characteristics were obtained by combining detailed information on butterfly distributions in Europe (which also led to the ‘Distribution Atlas of Butterflies in Europe’) and the corresponding climatic conditions. The presented dataset comprises information for the position and breadth of the following climatic niche characteristics: mean annual temperature, range in annual temperature, growing degree days, annual precipitation sum, range in annual precipitation and soil water content. The climatic niche position is indicated by the median and mean value for each climate variable across a species’ range, accompanied by the 95% confidence interval for the mean and the number of grid cells used for calculations. Climatic niche breadth is indicated by the standard deviation and the minimum and maximum values for each climatic variable across a species’ range. Database compilation was based on high quality standards and the data are ready to use for a broad range of applications.It is already evident that the information provided in this dataset is of great relevance for basic and applied ecology. Based on the species temperature index (STI, i.e. the mean temperature value per species), the community temperature index (CTI, i.e. the average STI value across the species in a community) was recently adopted as an indicator of climate change impact on biodiversity by the pan-European framework supporting the Convention on Biological Diversity (Streamlining European Biodiversity Indicators 2010) and has already been used in several scientific publications. The application potential of this database ranges from theoretical aspects such as assessments of past niche evolution or analyses of trait interdependencies to the very applied aspects of measuring, monitoring and projecting historical, ongoing and potential future responses to climate change using butterflies as an indicator.     

Modeling and mapping the current and future climatic-niche of endangered Himalayan musk deer

Identification of geographical space enveloped by suitable climatic conditions (i.e., climatic niche) that support species survival over space and time is crucial in conservation biogeography. Numerous algorithms (e.g., Maxent, GARP) with increasing accuracy have been devised and are being employed to overcome the challenges of forecasting climatic niche of species with incomplete information. The current study was conducted to map the distribution of current and future climatic niche of endangered Himalayan musk deer, a species endemic to Asia. Maxent and GARP modeling algorithms were individually employed to forecast current and future climatic niche of the species using randomly collected occurrence records of the species and bioclimatic variables with 30″ resolution from ‘WorldClim’ datasets. Both the modeling processes performed optimally with regard to AUC and TSS values and forecasted an increase/expansion of climatically-suitable geographical space in the future. A final climatic niche distribution map was produced by combining the binary maps generated from each of the processes to produce a relatively realistic and potentially accurate distribution of climatic niche of the species over space and time. Conservation of forecasted suitable geographical space is recommended and future survey efforts for potentially unexplored populations of the species in the forecasted suitable area are suggested.     

Overshooting dynamics in a model adaptive radiation

The history of life is punctuated by repeated periods of unusually rapid evolutionary diversification called adaptive radiation. The dynamics of diversity during a radiation reflect an overshooting pattern with an initial phase of exponential-like increase followed by a slower decline. Much attention has been paid to the factors that drive the increase phase, but far less is known about the causes of the decline phase. Decreases in diversity are rarely associated with climatic changes or catastrophic events, suggesting that they may be an intrinsic consequence of diversification. We experimentally identify the factors responsible for losses in diversity during the later stages of the model adaptive radiation of the bacterium Pseudomonas fluorescens. Proximately, diversity declines because of the loss of biofilm-forming niche specialist morphotypes. We show that this loss occurs despite the presence of strong divergent selection late in the radiation and is associated with continued adaptation of resident niche specialists to both the biotic and abiotic environments. These results suggest that losses of diversity in the latter stages of an adaptive radiation may be a general consequence of diversification through competition and lends support to the idea that the conditions favouring the emergence of diversity are different from those that ensure its long-term maintenance.     

Evidence for shared broad‐scale climatic niches of diploid and polyploid plants

Whole‐genome duplication (polyploidy) occurs frequently and repeatedly within species, often forming new lineages that contribute to biodiversity, particularly in plants. Establishment and persistence of new polyploids may be thwarted by competition with surrounding diploids; however, climatic niche shifts, where polyploids occupy different niches than diploid progenitors, may help polyploids overcome this challenge. We tested for climatic niche shifts between cytotypes using a new ordination approach and an unprecedentedly large data set containing young, conspecific diploids and polyploids. Despite expectations of frequent niche shifts, we show evidence for alternative patterns, such as niche conservatism and contraction, rather than a prevalent pattern of niche shifts. In addition, we explore how interpreting climatic niches plotted on environmental niche (principal component) axes can generate hypotheses about processes underlying niche dynamics. Dispersal capabilities or other life‐history traits, rather than shifts to new climatic niches, could better explain polyploid persistence in the long term.     

Evolutionary and environmental determinants of freshwater fish thermal tolerance and plasticity

Understanding the extent to which phylogenetic constraints and adaptive evolutionary forces help define the physiological sensitivity of species is critical for anticipating climate‐related impacts in aquatic environments. Yet, whether upper thermal tolerance and plasticity are shaped by common evolutionary and environmental mechanisms remains to be tested. Based on a systematic literature review, we investigated this question in 82 freshwater fish species (27 families) representing 829 experiments for which data existed on upper thermal limits and it was possible to estimate plasticity using upper thermal tolerance reaction norms. Our findings indicated that there are strong phylogenetic signals in both thermal tolerances and acclimation capacity, although it is weaker in the latter. We found that upper thermal tolerances are correlated with the temperatures experienced by species across their range, likely because of spatially autocorrelated processes in which closely related species share similar selection pressures and limited dispersal from ancestral environments. No association with species thermal habitat was found for acclimation capacity. Instead, species with the lowest physiological plasticity also displayed the highest thermal tolerances, reflecting to some extent an evolutionary trade‐off between these two traits. Although our study demonstrates that macroecological climatic niche features measured from species distributions are likely to provide a good approximation of freshwater fish sensitivity to climate change, disentangling the mechanisms underlying both acute and chronic heat tolerances may help to refine predictions regarding climate change‐related range shifts and extinctions.     

ASYNCHRONOUS EVOLUTION OF PHYSIOLOGY AND MORPHOLOGY IN ANOLIS LIZARDS

Species‐rich adaptive radiations typically diversify along several distinct ecological axes, each characterized by morphological, physiological, and behavioral adaptations. We test here whether different types of adaptive traits share similar patterns of evolution within a radiation by investigating patterns of evolution of morphological traits associated with microhabitat specialization and of physiological traits associated with thermal biology in Anolis lizards. Previous studies of anoles suggest that close relatives share the same “structural niche” (i.e., use the same types of perches) and are similar in body size and shape, but live in different “climatic niches” (i.e., use habitats with different insolation and temperature profiles). Because morphology is closely tied to structural niche and field active body temperatures are tied to climatic niches in Anolis, we expected phylogenetic analyses to show that morphology is more evolutionarily conservative than thermal physiology. In support of this hypothesis, we find (1) that thermal biology exhibits more divergence among recently diverged Anolis taxa than does morphology; and (2) diversification of thermal biology among all species often follows diversification in morphology. These conclusions are remarkably consistent with predictions made by anole biologists in the 1960s and 1970s.     

Temperature dependent sex determination and climate change

One possible response of species to climate change is shifting their geographical range so as to track their climatic niche. Many concerns have been raised about the species ability to disperse effectively. I argue that species may have mechanisms, like temperature-dependent sex determination (TSD), that are responsive to climate change and may facilitate an appropriate shift in their geographical range. More specifically, I hypothesize that, under stable climatic conditions, populations of some TSD species at the edge of their range are regulated by reduced growth rate (due to skewed sex ratios or due to limited availability of suitable nesting sites). Under climate change, these populations face new climatic conditions that trigger fast population growth (e.g. by more balanced sex ratio, or greater availability of nesting sites). Increased population size may lead to increased dispersal, and thus efficient colonization of the newly created habitat patches. So, the species rapidly tracks the geographical position of its climatic niche. This conceptual model is speculative but it leads to specific hypotheses, and opens up new research questions about the existence of prior adaptations that will enable the appropriate response to climate change.