Parasites form an integral part of food webs, however, mechanistic insights into the role of parasites for energy flow and community dynamics is currently limited by a lack of conceptual studies investigating host-parasite interactions in a community context. In aquatic systems, chytrids constitute a major group of fungal parasites and their free-living infective stage (zoospores) forms a highly nutritional food source to zooplankton. Consumption of zoospores can create an energy pathway from otherwise inedible phytoplankton to zooplankton (“mycoloop”). The impact of such parasite-mediated energy pathways on community dynamics and energy transfer to higher trophic levels is of high importance considering eutrophication and global warming induced shifts to dominance of unfavourable prey such as cyanobacteria. We theoretically investigated community dynamics and energy transfer in a food web consisting of an edible-nonhost and an inedible-host phytoplankton species, a fungal parasite, and a zooplankton species grazing on edible phytoplankton and fungi. Food web dynamics were investigated along a nutrient gradient for two cases: (1) non-adaptive zooplankton species representative for filter feeders like cladocerans and (2) zooplankton with the ability to actively adapt their feeding preferences like many copepod species. For both feeding strategies, the importance of the mycoloop for zooplankton increases with nutrient availability. This increase is smooth for non-adaptive consumers. For a consumer with an adaptive feeding preference, we observe an abrupt shift from almost exclusive preference for edible phytoplankton (dominant prey) at low nutrient levels to a strong preference for parasitic fungi at high nutrient levels. The model predicts that parasitic fungi can contribute up to 50% of the zooplankton diet in nutrient rich environments, agreeing with empirical observations on zooplankton gut content from eutrophic systems during cyanobacterial blooms. Our findings highlight the role of parasite-mediated energy pathway for predictions on energy flow and community composition under environmental change.
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.
Patterns of biodiversity provide insights into the processes that shape biological communities around the world. Variation in species diversity along biogeographical or ecological gradients, such as latitude or precipitation, can be attributed to variation in different components of biodiversity: changes in the total abundance (i.e. more-individual effects) and changes in the regional species abundance distribution (SAD). Rarefaction curves can provide a tool to partition these sources of variation on diversity, but first must be converted to a common unit of measurement. Here, we partition species diversity gradients into components of the SAD and abundance using the effective number of species (ENS) transformation of the individual-based rarefaction curve. Because the ENS curve is unconstrained by sample size, it can act as a standardized unit of measurement when comparing effect sizes among different components of biodiversity change. We illustrate the utility of the approach using two datasets spanning latitudinal diversity gradients in trees and marine reef fish, and find contrasting results. Whereas the diversity gradient of fish was mostly associated with variation in abundance (86%), the tree diversity gradient was mostly associated with variation in the SAD (59%). These results suggest that local fish diversity may be limited by energy through the more-individuals effect, while species pool effects are the larger determinant of tree diversity. We suggest that the framework of the ENS-curve has the potential to quantify the underlying factors influencing most aspects of diversity change.
An upsurge in anthropogenic climate change has accelerated the habitat loss and fragmentation of wild animal and plants. The rare and endangered plants is an important elements of biodiversity, but holistic conservation management has been hampered by lacking of detailed and reliable information about their spatial distribution. Our aim is to study the consequences of climate change on geographical distributions of a rare tree species Firmiana kwangsiensis (Malvaceae) to provide reference for conservation, introduction and cultivation of this species. Based on 30 effective occurrence records and 27 environmental variables, we modeling the potential distribution of F. kwangsiensis under current and two future climate scenarios in maximum entropy. We found that the potential suitable habitat boundary of F. kwangsiensis were limited by precipitation-associated variables and temperature-associated variables. Our model predicted 259,504 km2 of F. kwangsiensis habitat based on 25 percentile thresholds in contemporary, of which the high suitable area is about 41,027 km2. Guangxi’s protected areas provide the most coverage for F. kwangsiensis habitat. However, the existing reserves encompass 2.7% of the total suitable habitat and 4.2% of the high suitable habitat, which is lower than the average protection intensity in Guangxi (7.2%), meaning protected areas network is currently insufficient and alternative conservation mechanisms are needed to protect the habitat. Our findings will help to identify additional localities where F. kwangsiensis may exist, and also where it may spread to. It provides important information for the conservation management and cultivation of such rare tree species.
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.
The idea that populations are spatially structured has become a very powerful concept in ecology, raising interest in many research areas. However, despite dispersal being a core component of the concept, it typically does not consider the movement behavior underlying any dispersal. Using individual-based simulations in continuous space, we investigate the emergence of a spatially structured population in landscapes with spatially heterogeneous resource distribution and with organisms following simple area-concentrated search (ACS); individuals do not, however, perceive or respond to any habitat attributes per se but only to their foraging success. We investigated effects of different resource clustering pattern in landscapes (single large cluster vs. many small clusters) and different resource density on spatially structure of populations and movement between resource clusters of individuals. As results, we found that foraging success increased with increasing resource density and decreasing number of resource clusters. In a wide parameter space, the system exhibited attributes of a spatially structured populations with individuals concentrated in areas of high resource density, searching within areas of resources, and ‘dispersing’ in straight line between resource patches. ‘Emigration’ was more likely from patches that were small or of low quality (low resource density), but we observed an interaction effect between these two parameters. With the ACS implemented, individuals tended to move deeper into a resource cluster in scenarios with moderate resource density than in scenarios with high resource density. ‘Looping’ from patches was more likely if patches were large and of high quality. Our simulations demonstrate that spatial structure in populations may emerge if critical resources are heterogeneously distributed and if individuals follow simple movement rules (such as ACS). Neither the perception of habitat nor an explicit decision to emigrate from a patch on the side of acting individuals are necessary for the emergence of spatial structure.
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.
Sexual signals are important in speciation, but understanding their evolution is complex as these signals are often composed of multiple, genetically interdependent components. To understand how signals evolve, we thus need to consider selection responses in multiple components and account for the genetic correlations among components. One intriguing possibility is that selection changes the genetic covariance structure of a multicomponent signal in a way that facilitates a response to selection. However, this hypothesis remains largely untested empirically. In this study, we investigate the evolutionary response of the multicomponent female sex pheromone blend of the moth Heliothis subflexa to 10 generations of artificial selection. We observed a selection response of about 3/4s of a phenotypic standard deviation in the components under selection. Interestingly, other pheromone components that are biochemically and genetically linked to the components under selection did not change. We also found that after the onset of selection, the genetic covariance structure diverged, resulting in the disassociation of components under selection and components not under selection across the first two genetic principle components. Our findings provide rare empirical support for an intriguing mechanism by which a sexual signal can respond to selection without possible constraints from indirect selection responses.
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 maternally-inherited endosymbiont, Wolbachia, is known to alter the reproductive biology of its arthropod hosts for its benefit and can induce both positive and negative fitness effects in many hosts. Here we describe the effects of the maintenance of two distinct Wolbachia infections, one each from supergroups A and B, on the parasitoid host Nasonia vitripennis. We compare the effect of Wolbachia infections on various traits between the uninfected, single A infected, single B infected, and the double infected strains with their cured versions. Contrary to the previous reports, our results suggest that there is a significant cost associated with the maintenance of Wolbachia infections where traits like family size, fecundity, longevity, and rates of male copulation are compromised in Wolbachia infected strains. The double infected and supergroup B infection strains show higher Wolbachia titer than supergroup A. The double infected Wolbachia strain has the most detrimental impact on the host as compared to single infections. Moreover, there is a supergroup-specific negative impact on these wasps as the supergroup B infections elicit the most pronounced negative effects. These findings raise important questions on the mechanism of survival and maintenance of these reproductive parasites in arthropod hosts.
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.