Herbivory serves as a critical top-down mechanism within plant communities by regulating biodiversity, productivity, and ecosystem function. While top-down impacts of mammalian herbivores have garnered significant attention in the literature, fewer studies have investigated the role of herbivorous reptiles in regulating plant communities, which can serve as crucial herbivores in some ecosystems. In Southeastern United States coastal plain long-leaf pine forests, the gopher tortoise (Gopherus polyphemus) is a keystone species that may suppress plant productivity and promote local diversity within hyper-diverse understory plant communities. In January 2019, we established tortoise-exclusion plots within an active gopher tortoise population at Splinter Hill Bog Preserve in southwest Alabama, USA. We measured the response of plant species diversity, composition. and productivity through a single growing season to quantify the short-term impacts of tortoise-excluded plots on understory plant communities. We found that plots excluded tortoises had 35% more plant cover with a 15% reduction in plant richness, 6% reduction in evenness, and 12% reduction in Shannon’s diversity relative to control plots. Within a single growing season, we found that tortoise exclusion explained 5% of the variation within overall plant community composition. Our results provide clear evidence on the role of gopher tortoise herbivory for the maintenance of plant diversity within the species-rich longleaf pine forests of the Southeastern United States, even at short time scales and in an heterogeneous environment.
Giant clams are keystone species on coral reefs, but global demand for their harvest has decimated populations and resulted in all Tridacnids being listed on both CITES and IUCN lists. However, giant clams are notoriously difficult to identify, and recent molecular work has revealed that morphological misidentification of giant clams have confounded current population assessments and extinction risk. The most recent study of the status of giant clams in the Samoan Archipelago was published over 20 years ago, without molecular corroboration of visual identifications. Using morphologic characteristics and ez-RAD genetic techniques, we identify the existence of Tridacna noae in the Samoan archipelago, presenting the first observation and a resulting range expansion. Accurately identifying the extant species in the archipelago is the first step towards a much-needed population status assessment to effectively manage these long-lived species.
1. Bumble bees are key pollinators with some species reared in captivity at a commercial scale, but with evidence of population declines and with alarming predictions under climate change scenarios. While studies on the thermal biology of temperate species are still limited, they are entirely absent from the tropics where the effects of climate change are expected to be greater. 2. Herein we test if tropical bumble bees’ lower (CTMin) and upper (CTMax) critical thermal limits decrease with elevation and if the stable optimal conditions used in laboratory-reared colonies reduces their thermal tolerance. 3. We assessed changes in CTMin and CTMax of four species at two elevations (2600 and 3600 m) in the Colombian Andes and of laboratory-reared individuals of B. pauloensis. In addition, we examined the effect of body size and compiled information on bumble bees’ thermal limits from the literature to assess potential predictors for broad-scale patterns of variation. 4. CTMin decreased with elevation while CTMax did not. CTMax was slightly higher (0.84 °C) in laboratory-reared than in wild-caught bees while CTMin was similar. CTMin decreased with increasing body size while CTMax did not. Latitude is a good predictor for variations in CTMin while annual mean temperature and extreme monthly temperatures are good predictors for both CTMin and CTMax. 5. The stronger response in CTMin with increasing elevation supports Brett’s heat-invariant hypothesis. Tropical bumble bees appear to be about as heat tolerant as those from temperate areas, suggesting that other aspects of climate besides temperature (e.g., water balance) might be more determinant environmental factors for these species under global warming. Laboratory-reared colonies are adequate surrogates for addressing questions on thermal tolerance and global warming impacts.
Sweet taste is a primary sensation for the preference and adaption of primates to diet, which is crucial for their survival and fitness. It is clear now that the sweet perception is mediated by a G protein-coupled receptor (GPCR)-sweet taste receptor T1R2/T1R3, and many behavioral or physiological experiments have revealed the diverse sweet taste preferences and sensitivities in primates. However, the structure-function relationship of T1R2s/T1R3s in primates, especially the molecular basis for their species-specific sweet taste, has not be well understood until now. In this study, we performed a comprehensive sequence, structural and functional analysis of sweet taste receptors in primates to elucidate the molecular determinants mediating their species-dependent sweet taste recognition. Our results indicate obviously distinct taxonomic distribution and classification, as well as significant characteristics (interaction, coevolution and epistasis) for several subsets of function-related potential residues, which could partly account for the previously reported behavioral and physiological results of taste perception in primates. Moreover, the prosimians Lemuriformes species, which were reported to have no sensitivity to aspartame, could be proposed to be aspartame tasters based on the present analysis. Collectively, our study provides new insights and promotes a better understanding for the diversity, function and evolution of sweet taste receptors in primates.
The Arctic Warbler (Phylloscopus borealis) is a cryptic songbird that uses a Nearctic-Paleotropical migratory strategy. Using geolocators, we provide the first documentation of the migratory routes and wintering locations of two territorial adult male Arctic Warblers from Denali National Park and Preserve, Alaska. After accounting for position estimation uncertainties and biases, we found that both individuals departed their breeding grounds in early September, stopped over in southeastern Russia and China during autumn migration, then wintered in the Philippines and the island of Palau. Our documentation of Arctic Warbler wintering on Palau suggests that additional study is needed to document their wintering range. These results suggest that Arctic Warblers may migrate further overwater than previously thought and provide hitherto unknown information on stopover and wintering locations.
Climate change affects the species spatio-temporal distribution deeply. However, how climate affects the spatio-temporal distribution pattern of related species on the large scale remains largely unclear. Here, we selected two closely related species in Taxus genus Taxus chinensis and Taxus mairei to explore their distribution pattern. Four environmental variables were employed to simulate the distribution patterns using the optimized Maxent model. The results showed that the highly suitable area of T. chinensis and T. mairei in current period was 1.964×105km2 and 3.074×105km2, respectively. The distribution area of T. chinensis was smaller than that of T. mairei in different periods. Temperature and precipitation were the main climate factors that determined the potential distribution of the two species. The centroids of T. chinensis and T. mairei were in Sichuan and Hunan province in current period, respectively. In the future, the centroid migration direction of two species was almost opposite. T. chinensis would shift towards southwest, while T. mairei towards northeast. Our results revealed that the average elevation distribution of T. chinensis was higher than that of T. mairei. This study sheds new insights into the habitat preference and limiting environment factors of the two related species and provides a valuable reference for the conservation of these two endangered species.
Studies have shown negative impacts of increased human pressures on biodiversity at local (alpha-diversity) and regional (gamma-diversity) scales. However, the diversity between local sites (beta-diversity) has received less attention. This is an important shortcoming since beta-diversity acts as a linkage between trends at the local and regional scales. Decreased beta-diversity means that local sites lose their distinctiveness, becoming more similar to each other. This process, known as biotic homogenization, is predicted to arise through the replacement of native specialists with native and non-native generalists. However, the mechanisms causing biotic homogenization have not been fully studied nor its impacts on different facets of biodiversity. We examined if land-use change due to human actions causes biotic homogenization of taxonomic, functional and phylogenetic diversity in bird communities of forested habitats in the state of Minnesota, USA. Our aim was to study if increased human pressure, which included human population density, land transformation, transport infrastructure, and electrical power infrastructure, was associated with increased similarity among bird point count sites. Our results showed that elevated human pressure was not related with increased biotic homogenization in this study region. Interestingly, increased human pressure appeared to increase the between-site functional diversity of bird communities. This association was driven by a decrease in local diversity, which, due to the nature of beta-diversity, led to an increase in between-site diversity. We highlight the importance of considering multiple facets of biodiversity and the use of beta-diversity in a conservation setting.
The context and cause of adaptive radiations has been widely described and explored but why rapid evolutionary diversification does not occur in related evolutionary lineages has yet to be understood. One possible answer to this is simply that evolutionary diversification is provoked by environmental diversity, and that some lineages do not encounter the necessary environmental diversity. Three-spined stickleback on the Scottish island of North Uist show enormous diversification, which seems to be associated with the diversity of aquatic habitats. Stickleback on the neighbouring island of South Uist have not been reported to show the same level of evolutionary diversity, despite levels of environmental variation that we might expect to be similar to North Uist. In this study, we compared patterns of morphological and environmental diversity on North and South Uist. Ancestral anadromous stickleback from both islands exhibited similar morphology including size and bony ‘armour’. Resident stickleback showed significant variation in armour traits in relation to pH of water. However, North Uist stickleback exhibited greater diversity of morphological traits than South Uist and this was associated with greater diversity in pH of the waters of lochs on North Uist. Highly acidic and highly alkaline freshwater habitats are missing, or uncommon, on South Uist. Thus, pH appears to act as a causal factor driving the evolutionary diversification of stickleback in local adaptation in North and South Uist. This is consistent with diversification being more associated with ecological constraint than ecological opportunity.
1.The decline of biodiversity is threatening important ecosystem processes, yet this decline is not homogeneous with species presenting specific traits being more prone to extinction, potentially leading to disruption of key ecosystem functions. Ants are ubiquitous and provide a plethora of ecosystem functions and thus are well suited for studies assessing functional ecology. Within communities, interspecific body size can vary by several orders of magnitude. Our understanding of the efficiency of ecosystem processes by groups in function of their body size remains unexplored due to a lack of adequate methodology for an easy and accurate assessment of their respective contributions. 2. We describe a novel and modular methodology that selects ant individuals as a function of body size using two parameters: height and size of the access point. After assessing the efficiency of this method to separate access to bait by body size, we tested the hypothesis that resource removal is influenced by body size, and that larger species are more efficient. We segregated body size into distinct categories and tested the efficacy of this design using ground-dwelling ant communities. We quantified the amount removed from a protein bait by each size group as a proxy for scavenging. 3. This methodology successfully segregated individuals based on their body size, partitioning the ant community into three main groups presenting significantly different average size in all four metrics measured. In addition, we found that larger species disproportionally contributed to resource removal, with an efficiency 34 to 92 times higher per individual than smaller species. 4. This approach provides a new, adjustable methodology for in-situ differential exclusion, and highlights the role that different size groups play within a community, thus opening new opportunities to study the relative role of species, and the importance of ecological interactions in shaping ecosystem functions.
Aim: North China leopard (Panthera pardus japonensis), is the most widespread subspecies of leopard and one of the rare and endangered species in China. It is currently confined to several isolated reserves, and little is known about its habitat network connectivity with land use changes. We proposed an approach for the evaluation of the impacts of land use changes on landscape connectivity for North China leopard. Location: The Great Taihang Region, in the north of China, covers the entire territory of Shanxi province, as well as some districts and counties in Beijing, Hebei and Henan provinces. Methods: We analysed multiple background layers affecting North China leopard movement patterns, including environmental and anthropogenic factors, and generated a landscape resistance surface. Then we used Circuit theory-based connectivity models to delineate pathways suitable for species movement, and evaluate the connectivity status of core areas and the impacts of land use changes on landscape connectivity. Results: We identified 33 least cos distance paths in 1990 and 34 paths in 2020, and four key barrier areas. The landscape connectivity has not been greatly improved with the land use changes, especially with the increase of forest land from 26.61 to 34.85%. Nevertheless, there is a decreasing trend on connectivity in some key movement barrier areas. Improving landscape connectivity at a broad spatial scale is as important as protecting the habitats (natural reserves) where the species lived. Main conclusions: Our study can serve as an example of how to explore the relationships between land use changes and landscape connectivity for species at broad spatial scales with limited movement patterns data. This information is proved to be critical for enhancing landscape connectivity for conservation concern of North China leopard and planning of natural reserves network.
Climate change is increasing aridity in grassland and desert habitats across the southwestern United States, reducing available resources and drastically changing the breeding habitat of many bird species. Increases in aridity reduce sound propagation distances, potentially impacting habitat soundscapes, and leading to a breakdown of the avian soundscapes in the form of loss of vocal culture, reduced mating opportunities, and local population extinctions. We developed an agent-based model to examine how changes in aridity will affect both sound propagation and the ability of territorial birds to audibly contact their neighbors. We simulated vocal signal attenuation under a variety of environmental scenarios for the south central semi-arid prairies of the United States, ranging from contemporary weather conditions to predicted extremes under climate change. We also simulated how changes in physiological conditions, mainly evaporative water loss (EWL), would affect singing behavior. Under extreme climate change conditions, we found significantly fewer individuals successfully contacted all adjacent neighbors than did individuals in either the contemporary or mean climate change conditions. We also found that at higher sound frequencies and higher EWL, fewer individuals were able to successfully contact all of their neighbors, particularly in the extreme and extreme climate change conditions. These results indicate that climate change-mediated aridification may disrupt the avian soundscape, such that vocal communication no longer effectively functions for mate attraction or territorial defense. As climate change progresses increased aridity in current grasslands may favor shifts toward low frequency songs, colonial resource use, and altered songbird community compositions.
Phenotypic plasticity in reproductive behaviour can be a strong driver of individual fitness. For example, in species with high intra-sexual competition, changes in socio-sexual context can trigger quick adaptive plastic responses in males. In particular, a recent study in the vinegar fly (Drosophila melanogaster) shows that males respond adaptively to perception of female cues in a way that increases their reproductive success, but we ignore the underlying mechanisms of this phenomenon. Here, we aimed to fill this gap by investigating the short-term effects of female perception on male pre- and post-copulatory components of reproductive success: a) mating success, b) mating latency and duration, c) sperm competitiveness, and d) ejaculate effects on female receptivity and oviposition rate. We found that brief sexual perception increased mating duration, but had no effect on the main pre- or post-copulatory fitness proxies. These results tie up with previous findings to suggest that male adaptive responses to sexual perception are not due to a short-term advantage, but rather to fitness benefits that play out across the entire male lifespan.
Anthropogenic and climatic factors affect the survival of animal species. Chinese pangolins are a critically endangered species, and identifying which variables lead to local extinction events is essential for conservation management. Local chronicles in China serve as long-term monitoring data, providing a perspective to disentangle the roles of human impacts and climate changes in local extinctions. Through a generalized additive model, extinction risk assessment model and principal component analysis, we combined information from local chronicles over a period of three hundred years (1700-2000) and reconstructed environmental data to determine the causes of local extinctions of the Chinese pangolin in China. Our results showed that the extinction probability increased with population growth and climate warming. An extinction risk assessment indicated that the population and distribution range of Chinese pangolins has been persistently shrinking in response to highly intensive human activities (main cause) and climate warming. Overall, the factors that cause local extinction, intensive human interference and drastic climatic fluctuations induced by global warming, might increase the local extinction rate of Chinese pangolins. Approximately 25% of extant Chinese pangolins are confronted with a notable extinction risk (0.36≤extinction probability≤0.93), specifically those distributed in Southeast China, including Guangdong, Jiangxi, Zhejiang, Hunan, Fujian, Jiangsu and Taiwan Provinces. To rescue this endangered species, we suggest strengthening field investigations, identifying the exact distribution range and population density of Chinese pangolins and further optimizing the network of nature reserves to improve conservation coverage on the territory scale. Conservation practices that concentrate on the viability assessment of scattered populations could lead to the successful restoration of the Chinese pangolin population.
Understanding the factors that regulate the functioning of our ecosystems in response to environmental changes can help to maintain the stable provisioning of ecosystem services to mankind. This is especially relevant given the increased variability of environmental conditions due to human activities. In particular, maintaining a stable production and plant biomass during the growing season (intra-annual stability) despite pervasive and directional changes in temperature and precipitation through time can help to secure food supply to wild animals, livestock, and humans. Here, we conducted a 29-year field observational study in a temperate grassland to explore how the intra-annual stability of primary productivity is influenced by biotic and abiotic variables through time. In particular, we analyzed the relationship of community biomass intra-annual stability with plant diversity and seasonal distribution patterns of temperature and precipitation. We found that lower accumulated precipitation between June and September during the 29-year investigated contributed to lower intra-annual community stability because of a decrease in compensatory mechanisms among species (species asynchrony). Additionally, higher precipitation in July contributed to higher intra-annual stability because higher species richness with higher precipitation led to higher average intra-annual stability of all species in the community (species stability). In contrast, we found no evidence that temperature influenced community intra-annual stability. Our results indicates that ongoing reduced seasonal precipitation leading to reduced intra-annual stability in the temperate grassland, which has important theoretical significance for us to take active measures to deal with climate change.
The non-breeding period represents a significant part of an Afro-Palearctic migratory bird’s annual cycle. Decisions such as whether to remain at a single site and whether to return to it across years have important effects on aspects such as survival, future breeding success, migratory connectivity, and conservation. During this study, we colour-ringed > 300 Common Whitethroats Curruca communis and undertook daily resightings to understand site persistence and the degree of site fidelity throughout three non-breeding periods (November – April) in Nigeria. The probability of detecting a colour-ringed Whitethroat when it was present, was 0.33. Site persistence varied widely across individuals (1 – 165 days) and did not differ significantly with sex or year, though first-year birds remained for significantly shorter periods than adults. We believe that shorter residencies are likely due to the use of multiple stationary non-breeding sites rather than low winter survival. A minimum of 19% of individuals returned to the study site the following year and shifted, on average, 300 meters, suggesting that Whitethroats have a relatively high degree of between-years site fidelity at a very fine scale. An individual’s previous residency duration did not seem to determine its residency duration the following year. We suggest that spatial fidelity is high and constant through years, but temporal fidelity is not, and individual residency patterns vary, probably according to yearly and seasonal conditions. Our results highlight the complexity of the annual cycle of a single species and the importance of carrying out in situ, small scale research throughout a migrant’s annual cycle over several years.
The critical information for conserving endangered species is to identify how different niche dimensions affect the bottlenecks in the life history stages of populations. However, it is often difficult to quantify how each niche dimension affects different life history stages because environmental factors may affect each fitness component of organisms to various degrees. Here, we applied the recently developed hypervolume method that follows the idea of Hutchinson’s n-dimensional hypervolume. We analyzed the niche space of different life history stages of the endangered landlocked salmon Oncorhynchus masou formosanus, the most southerly distributed of all salmonoids. We found no direct effect of water pollution on adult population density but a significant negative effect on their embryo hatching rate. Surprisingly, the niche hypervolume analysis showed that the size of embryo niche hypervolume was only 42% and 45.3% of the natural redd density or adult population density, respectively. This result suggests that water quality requirements during the embryonic stage are a key bottleneck in the life history stages of O. m. formosanus. Our results suggest that understanding the behavioral and physiological mechanisms that influence crucial life history stages in the wild is critical to developing effective conservation programs, and the niche hypervolume is a valuable method to achieve this.
Growth and growth limitation are important indicators of density dependence and environmental limitation of populations. Estimating individual growth trajectories is therefore an important aspect of understanding and predicting the life history and dynamics of a population. Variation in individual growth trajectories arises due to variation in the environmental factors limiting individual growth. This environmental limitation can vary over time, between cohorts and between individuals within a cohort. For a complete and accurate understanding of individual growth in a population, it is important to include all these sources of variation. So far, statistical models only accounted for a subset of these factors or required an extensive growth history of individuals. Here we present a novel model describing the growth curves of cohorts in a population. This model is derived from a stochastic form of the Von Bertalanffy growth equation describing individual growth. The model is specifically tailored for use on length-at-age data in which the growth trajectory of an individual is unknown and every individual is only measured once. The presented method can also be used if growth limitation differs strongly between age or length classes. We demonstrate the use of the model for length-at-age data of North Sea plaice (Pleuronectes platessa) from the last thirty years. Fitting this model to length-at-age data can provide new insights in the dynamics of the environmental factors limiting individual growth and provides a useful tool for ecological research and management.
The estimation of demographic parameters is a key component of evolutionary demography and conservation biology. Capture-mark-recapture methods have served as a fundamental tool for estimating demographic parameters. The accurate estimation of demographic parameters in capture-mark-recapture studies depends on accurate modeling of the observation process. Classic capture-mark-recapture models typically model the observation process as a Bernoulli or categorical trial with some detection probability conditional on a marked individual’s availability for detection (e.g., alive, or alive and present in a study area). Alternatives to this approach are underused, but may have great utility in capture-recapture studies. In this paper we explore a simple concept: in the same way that counts contain more information about abundance than simple detection/non-detection data, the number of encounters of individuals during observation occasions contain more information about the observation process than detection/non-detection data for individuals during the same occasion. Rather than using Bernoulli or categorical distributions to estimate detection probability, we demonstrate the application of zero-inflated Poisson and gamma-Poisson distributions. This allows for inference on availability for encounter (i.e., temporary emigration), as well as a wide variety of parameterizations for heterogeneity in the observation process. We demonstrate that this approach can accurately recover demographic and observation parameters in the presence of individual heterogeneity in detection probability, and discuss some potential future extensions of this method.