1. Trait differences among plant species can favor species coexistence. The role that such differences play in the assembly of diverse plant communities maintained by frequent fires remains unresolved. This lack of resolution results in part from the possibility that species with similar traits may coexist because none has a significant fitness advantage and in part from the difficulty of experimental manipulation of highly diverse assemblages dominated by perennial species. 2. We examined a 65-year chronosequence of losses of herbaceous species following fire suppression (and subsequent encroachment by Pinus elliottii) in three wet longleaf pine savannas. We used cluster analysis, similarity profile permutation tests and k-R cluster analysis to identify statistically significant functional groups. We then used randomization tests to determine if the absence of functional groups near pines was greater (or less) than expected by chance. We also tested whether tolerant and sensitive species were less (or more) likely to co-occur by chance in areas in savannas away from pines in accordance with predictions of modern coexistence theory. 3. Functional group richness near pines was lower than expected from random species extirpations. Wetland perennials with thick rhizomes and high leaf water content, spring-flowering wetland forbs (including Drosera tracyi), orchids, Polygala spp., and club mosses were more likely to be absent near pines than expected by chance. C3 grasses and sedges with seed banks and tall, fall-flowering C4 grasses were less likely to be absent near pines than expected by chance. Species sensitive to pine encroachment were more likely to co-occur with other such species away from pines at two of the three sites. 4. Results suggest that herb species diversity in frequently-burned wet savannas is maintained in part by a weak fitness (e.g., competitive) hierarchy among herbs, and not as a result of trait differences among co-occurring species.
1. Almost all organisms grow in size during their lifetime and switch diets, trophic positions, and interacting partners as they grow. Such ontogenetic development introduces life-history stages and flows of biomass between the stages through growth and reproduction. However, current research on complex food webs rarely considers life-history stages. The few previously proposed methods do not take full advantage of the existing food web structural models that can produce realistic food web topologies. 2. We extended the niche model by Williams & Martinez (2000) to generate food webs that included trophic species with a life-history stage structure. Our method aggregated trophic species based on niche overlap to form a life-history structured population; therefore, it largely preserved the topological structure of food webs generated by the niche model. We applied the theory of allometric predator-prey body mass ratio and parameterized an allometric bioenergetic model augmented with biomass flow between stages via growth and reproduction to study the effects of a stage structure on the stability of food webs. 3. When life-history stages were linked via growth and reproduction, fewer food webs persisted while persisting food webs tended to retain more trophic species. Topological differences between persisting linked and unlinked food webs were small to modest. Temporal variability of biomass dynamics and slopes of biomass spectra were lower in the linked food webs than the unlinked ones, suggesting that a life-history stage structure enhanced stability of complex food webs. 4. Our results suggest a positive relationship between the complexity and stability of complex food webs. A life-history stage structure in food webs may play important roles in dynamics of and diversity in food webs.
Research hypotheses have been a cornerstone of science since before Galileo. Many have argued that inclusion of multiple hypotheses (1) encourage discovery of mechanisms, and (2) reduce bias – both features that should increase transferability and reproducibility. However, we are entering a new era of big data and highly predictive models where some argue the hypothesis is outmoded. Indeed, using a detailed literature analysis, we found prevalence of hypotheses in eco-evo research is very low (6.7-26%) and static from 1990-2015, a pattern mirrored in an extensive literature search (N=302,558 articles). Our literature review also indicates that neither grant success or citation rates were related to the inclusion of hypotheses, which may provide disincentive for hypothesis formulation. Here we confront common justifications for avoiding hypotheses and present new arguments based on benefits to the individual. Although hypotheses are not always necessary, we expect their continued and increased use will help our fields move toward greater understanding, reproducibility, prediction, and effective conservation of nature.
Both termites and large mammalian herbivores (LMH) are savanna ecosystem engineers that have profound impacts on ecosystem structure and function. Both of these savanna engineers modulate many common and shared dietary resources such as woody and herbaceous plant biomass, yet few studies have addressed how they impact one another. In particular, it is unclear how herbivores may influence the abundance of long-lived termite mounds via changes in termite dietary resources such as woody and herbaceous biomass. While it has long been assumed that abundance and areal cover of termite mounds in the landscape remains relatively stable, most data are observational, and few experiments have tested how termite mound patterns may respond to biotic factors such as changes in large herbivore communities. Here, we use a broad tree density gradient and two landscape-scale experimental manipulations—the first a multi-guild large herbivore exclosure experiment and the second a tree removal experiment– to demonstrate that patterns in termite mound abundance and cover are unexpectedly dynamic. Termite mound abundance, but not areal cover not significantly, is positively associated with experimentally controlled presence of cattle, but not wild mesoherbivores (15-1000 kg) or megaherbivores (elephants and giraffes). Herbaceous productivity and tree density, termite dietary resources that significantly affected by different LMH treatments, are both positive predictors of termite mound abundance. Experimental reductions of tree densities are associated with lower abundances of termite mounds. These results reveal a richly interacting web of relationships among multiple savanna ecosystem engineers and suggest that termite mound abundance and areal cover is intimately tied to herbivore-driven resource availability.
1. The description and analysis of animal behaviour over long periods of time is one of the most important challenges in ecology. However, most of these studies are limited due to the time and cost required by human observers. The collection of data via video recordings allows observation periods to be extended. However, their evaluation by human observers is very time-consuming. Progress in automated evaluation, using suitable deep learning methods, seems to be a forwardlooking approach to analyse even large amounts of video data in an adequate time frame. 2. In this study we present amulti-step convolutional neural network system for detecting animal behaviour states, which works with high accuracy. An important aspect of our approach is the introduction of model averaging and post-processing rules to make the system robust to outliers. 3. Our trained system achieves an in-domain classification accuracy of >0.92, which is improved to >0.96 by a postprocessing step. In addition, the whole system performs even well in an out-of-domain classification task with two unknown types, achieving an average accuracy of 0.93. We provide our system at https://github.com/Klimroth/Video-Action-Classifier-for-African-Ungulates-in-Zoos/tree/main/mrcnn_based so that interested users can train their own models to classify images and conduct behavioural studies of wildlife. 4. The use of a multi-step convolutional neural network for fast and accurate classification of wildlife behaviour facilitates the evaluation of large amounts of image data in ecological studies and reduces the effort of manual analysis of images to a high degree. Our system also shows that post-processing rules are a suitable way to make species-specific adjustments and substantially increase the accuracy of the description of single behavioural phases (number, duration). The results in the out-of-domain classification strongly suggest that our system is robust and achieves a high degree of accuracy even for new species, so that other settings (e.g. field studies) can be considered.
Diffusible iodine-based contrast-enhanced Computed-Tomography (diceCT) visualizes soft-tissue from microCT (µCT) scans of specimens to uncover internal features and natural history information without incurring physical damage via dissection. Unlike hard-tissue imaging, diceCT datasets are currently limited to a few individual specimens and taxonomically underrepresented. To initiate best practices for diceCT in a non-model group, we outline a guide for staining and high-throughput µCT scanning in snakes. We scanned the entire body and one region of interest (i.e., head) for 23 specimens representing 23 species from the clades Aniliidae, Dipsadinae, Colubrinae, Elapidae, Lamprophiidae and Viperidae. We generated 82 scans that include 1.25% Lugols iodine stained (soft tissue) and unstained (skeletal) data for each specimen. We found that duration of optimal staining time increased linearly with body size; head radius was the best indicator. Post-reconstruction of scans, optimal staining was evident by evenly distributed grayscale values and clear differentiation among soft-tissue anatomy. Under and over stained specimens produced poor contrast among soft-tissues, which was often exacerbated by user bias during “digital dissections” (i.e., segmentation). Regardless, all scans produced usable data from which we assessed a range of downstream analytical applications within ecology and evolution (e.g., predator-prey interactions, life history, and morphological evolution). Ethanol de-staining reversed the known effects of iodine on the exterior appearance of physical specimens, but required substantially more time than reported for other de-staining methods. We discuss the feasibility of implementing diceCT techniques for a new user, including approximate financial and temporal commitments, required facilities, and potential effects of staining on specimens. We present the first high-throughput workflow for full-body skeletal and diceCT scanning in snakes, which can be generalized to any elongate vertebrates, and increases publicly available diceCT scans for reptiles by an order of magnitude.
Aim The aim of this study is to model the past, current and future distribution of J. phoenicea s.s., J. turbinata and J. canariensis, based on bioclimatic variables using a maximum entropy model (MaxEnt) in the Mediterranean and Macaronesian regions. Location Mediterranean and Macaronesian Taxon Cupressaceae, Juniperus Methods Data on the occurrence of the J. phoenicea complex was obtained from the GBIF, the literature, herbaria, and the authors’ field notes. The bioclimatic variables were obtained from the WorldClim database (http://worldclim.org/) and Paleoclim (http://www.paleoclim.org/). The climate data related to species localities were used for predictions of niches by implementation of MaxEnt and we evaluated the model with ENMeval. Results The potential niches of Juniperus phoenicea during the LIG, LGM and MH covered 30%, 10% and almost 100%, respectively, of the current potential niche. Climate warming could reduce potential niches by 30% and 90% in scenarios RCP2.6 and RCP8.5, respectively. The potential niches of Juniperus turbinata had a broad circum-Mediterranean and Canarian distribution during the LIG and the MH, extending its distribution during the LGM when it was found in more areas than at present; the predicted warming in scenario RCP2.6 and RCP8.5 could reduce the current potential niche by 30% and 50%, respectively. The model did not find suitable niches for J. canariensis during the LIG and the LGM, but during the MH its potential niche was 30% larger than at present. The climate warming scenario RCP2.6 indicates a reduction of the potential niche by 30%, while RCP8.5 does so by almost 60%. Main conclusions This research can provide information to increase the protection of the juniper forest and to try to counteract the phenomenon of local extinctions caused by anthropic pressure and climate changes.
Alternative reproductive tactics (ARTs) have provided valuable insights into how sexual selection and life history tradeoffs can lead to variation within a sex. However, the possibility that tactics may constrain evolution through intralocus tactical conflict (IATC) is rarely considered. In addition, when IATC has been considered, the focus has often been on the genetic correlations between the ARTs, while evidence that the ARTs have different optima for associated traits and that at least one of the tactics is not at its optima is often missing. Here we investigate selection on three traits associated with the ARTs in the swordtail fish Xiphophorus multilineatus; body size, body shape and the sexually selected trait for which these fishes were named, sword length (elongation of the caudal fin). All three traits are tactically dimorphic, with courter males being larger, deeper bodied and having longer swords, and the sneaker males being smaller, more fusiform and having shorter swords. Using measures of reproductive success in a wild population we calculated selection differentials, linear and quadratic gradients, demonstrate that the tactics have different optima and at least one of the tactics is not at its optima for body size and sword length. Our results provide the first evidence of selection in the wild on the sword, an iconic trait for sexual selection. In addition, given the high probability that these traits are genetically correlated to some extent between the two tactics, our study suggests that IATC is constraining both body size and the sword from reaching their phenotypic optima. We discuss the importance of considering the role of IATC in the evolution of tactical dimorphism, how this conflict can be present despite tactical dimorphism, and how it is important to consider this conflict when explaining not only variation within a species but differences across species as well.
Many insects possess the plastic ability to either develop directly to adulthood, or enter diapause and postpone reproduction until the next year, depending on environmental cues (primarily photoperiod) that signal the amount of time remaining until the end of the growth season. These two developmental pathways often differ in co-adapted life history traits, e.g. with slower development and larger size in individuals headed for diapause. The developmental timing of these differences may be of adaptive importance: if pathways diverge late, the scope for phenotypic differences is smaller, whereas if pathways diverge early, the risk is higher of expressing a maladaptive phenotype if the selective environment changes. Here we explore the effects of changes in photoperiodic information during life on pupal diapause and associated life history traits in the butterfly Pararge aegeria. We find that both pupal diapause and larval development rate are asymmetrically regulated: while exposure to long days late in life (regardless of earlier experiences) was sufficient to produce nondiapause development and accelerate larval development accordingly, more prolonged exposure to short days was required to induce diapause and slow down pre-diapause larval development. While the two developmental pathways diverged early in development, development rates could be partially reversed by altered environmental cues. Meanwhile, pathway differences in body size were more inflexible, despite emerging late in development. Hence, in P. aegeria several traits are regulated by photoperiod, along subtly different ontogenies, into an integrated phenotype that strikes a balance between flexibility and phenotype-environment matching.
Kauri dieback, caused by Phytophthora agathidicida, is an ecosystem disturbance that poses a recent threat to the survival of kauri (Agathis australis) forests in New Zealand. Throughfall and stemflow play an important role in meeting the nutrient requirements of kauri forests. However, the effects of kauri dieback on canopy nutrient deposition remain unknown. Here we measured throughfall, stemflow and forest floor water yield and nutrient concentrations and fluxes (potassium, calcium, magnesium, manganese, silicon, sulphur, sodium, iron) of ten kauri trees differing in soil P. agathidicida DNA concentration and health status. We did not observe an effect of soil P. agathidicida DNA concentration on throughfall and stemflow water yield. Throughfall and forest floor nutrient concentrations and fluxes tended to decrease (up to 50%) with increasing soil P. agathidicida DNA concentration. Significant effects were found for potassium and manganese fluxes in throughfall, and calcium and silicon fluxes in forest floor leachate. The decline in nutrient input will have implications on plant nutrition, tree health and susceptibility to future pathogen infection in these ecologically unique kauri forests. Given our findings and the increasing spread of Phytophthora species worldwide, research on the underlying physiological mechanisms linking dieback and plant-soil nutrient fluxes is critical.
Seed recruitment is a major driver of mangrove restoration globally. It is hypothesized that soil condition and channel hydrology can accelerate seedling recruitment and regeneration after a major disturbance. Species abundance, diversity indices, microbial and chemical concentrations in sand-filled mangrove forest was studied. Eight plots (area = 3902.16 m2) were established with ten transects in each plot in a random block design to investigate the effect of soil conditions on seedling growth. A total of 1, 886 seedlings were physically counted. Seedling abundance was significantly different between red (Rizophora racemosa), white (Laguncularia racemosa) and black (Avicennia germinans) mangroves and nypa palm (nypa fruticans). The most dominant species was black mangroves and the least dominant species was nypa palm. Muddy soils had the most abundant species while sandy soils had the least abundant species. Furthermore, semi-muddy soils had the highest species diversity (H = 0.948) whereas muddy soils had the least species diversity (H = 0.022). The soil metal concentration has no correlation with seed abundance and occur in the order Iron>Nitrate>Copper>Cadmium. Soil with high species diversity had high soil microbial population; however, seedling abundance was correlated with soil nutrients and not heavy metals. Small seeds are easily recruited while good soil condition plus existing hydrological connection facilitated natural seedling regeneration in the disturbed mangrove forest.
Capture-mark-recapture (CMR) studies have been used extensively in ecology and evolution. While it is feasible to apply CMR in some animals, it is considerably more challenging in small fast-moving species such as insects. In these groups, low recapture rates can bias estimates of demographic parameters, thereby, handicapping effective management of wild populations. Here we use high-speed videos (HSV) of the adults of two large dragonfly species that rarely land and, thus, are particularly challenging for CMR studies. We specifically test whether HSV, compared to conventional eye observations, increases the “resighting” rates and improves the certainty of the estimates of survival rate, and the effects of demographic covariates on survival rates. We show that the use of HSV increases the number of resights substantially. HSV improved our estimates of resighting and survival probability which were either under- or overestimated with the conventional observations. HSV increased the accuracy of the estimates of effect sizes of important covariates (age and body size). Integrating HSV in CMR of highly mobile animals is valuable because it is easy, non-invasive, and has the potential to improve demographic estimates. Hence, it opens the door for a wide range of research possibilities on species that are traditionally difficult to monitor, including within insects, birds, and mammals.
1. Behavior and organization of social groups is thought to be vital to the functioning of societies, yet the contributions of various roles within social groups towards population growth and dynamics have been difficult to quantify. A common approach to quantifying these role-based contributions is evaluating the number of individuals conducting certain roles, which ignores how behavior might scale up to effects at the population-level. Manipulative experiments are another common approach to determine population-level effects, but they often ignore potential feedbacks associated with these various roles. 2. Here, we evaluate the effects of worker size distribution in bumblebee colonies on worker production in 24 observational colonies across three environments, using functional linear models. Functional linear models are an underused correlative technique that has been used to assess lag effects of environmental drivers on plant performance. We demonstrate potential applications of this technique for exploring high-dimensional ecological systems, such as the contributions of individuals with different traits to colony dynamics. 3. We found that more larger workers had mostly positive effects and more smaller workers had negative effects on worker production. Most of these effects were only detected under low or fluctuating resource environments suggesting that the advantage of colonies with larger-bodied workers becomes more apparent under stressful conditions. 4. We also demonstrate the wider ecological application of functional linear models. We highlight the advantages and limitations when considering these models, and how they are a valuable complement to many of these performance-based and manipulative experiments.
Elevation is involved in determining plant diversity in montane ecosystems. This study examined whether the species distribution of plants in the Yatsugatake Mountains, central Japan, substantiated hypotheses associated with an elevational diversity gradient. Species richness of trees, shrubs, herbs, ferns, and bryophytes was investigated in study plots established at 200-m elevational intervals from 1800 to 2800 m. The changes in plant diversity (alpha and beta diversities, plant functional types, and elevational ranges) with elevation were analyzed in relation to climatic factors and elevational diversity gradient hypotheses, that is, mass effect, mid-domain effect, and Rapoport’s elevational rule. A comparison of alpha and beta diversities revealed that different plant groups respond variably to elevation; the alpha diversity of trees and ferns decreased, that of herbs increased, whereas the alpha diversity of shrubs and bryophytes showed a U-shaped relationship and a hump-shaped pattern. The beta diversity of shrubs, herbs, and bryophytes increased above the subalpine–alpine transition ecotone. In accordance with these changes, the dominance of evergreen shrubs and graminoids increased above this ecotone, whereas that of evergreen trees and liverworts decreased. None of the plant groups showed a wide elevational range at higher elevations. These elevational patterns of plant groups were explained by climatic factors, and not by elevational diversity gradient hypotheses. These patterns were further influenced by plant–plant interactions via competition for light availability and physical habitat alternation.
The Lesser White-fronted Goose (Anser erythropus), smallest of the “grey” geese, is listed as Vulnerable on the IUCN Red List and protected in all range states. There are three sub-populations, with the least studied being the East Asian sub-population, shared between Russia and China. The extreme remoteness of breeding enclaves makes them largely inaccessible to researchers. As a substitute for visitation, remotely tracking birds from wintering grounds allows exploration of their summer range. Over a period of three years, and using highly accurate GPS tracking devices, eleven individuals of A. erythropus were tracked from the key wintering site of Dongting Lake, China, to breeding, molting, and staging sites in north-eastern Russia. Data obtained from that tracking, bolstered by ground survey and literature records, were used to model the summer distribution of A. erythropus. Although earlier literature suggests the summer range is patchy, the model confirms a contiguous summer range. The most suitable habitats are located along the coasts of the Laptev Sea, primarily the Lena-Delta, in the Yana-Kolyma Lowland, and smaller lowlands of Chukotka with narrow riparian extensions upstream along major rivers such as the Lena, Indigirka and Kolyma. The probability of A. erythropus presence is related to sites with altitude less than 500 m with abundant wetlands, especially riparian habitat, and a climate with precipitation of warmest quarter around 55 mm and mean temperature of wettest quarter around 14oC. Human disturbance also affects site suitability, with a gradual decrease in species presence starting around 160 km from human settlements. Remote tracking of animal species can bridge the knowledge gap required for robust estimation of species distribution patterns in remote areas. Better knowledge of species’ distribution is important in understanding the large-scale ecological consequences of rapid global change and establishing conservation management strategies.
Tree functional traits together with processes such as forest regeneration, growth, and mortality affect forest and tree structure. Forest management inherently impacts these processes. Moreover, forest structure, biodiversity, resilience, and carbon uptake can be sustained and enhanced with forest management activities. To assess structural complexity of individual trees, comprehensive and quantitative measures are needed, and they are often lacking for current forest management practices. Here, we utilized 3D information from individual Scots pine (Pinus sylvestris L.) trees obtained with terrestrial laser scanning (TLS) to first, assess effects of forest management on structural complexity of individual trees, and second, understand relationship between several tree attributes and structural complexity. We studied structural complexity of individual trees represented by a single scale independent metric called “box dimension”. This study aimed at identifying drivers affecting structural complexity of individual Scots pine trees in boreal forest conditions. The results showed that thinning increased structural complexity of individual Scots pine trees. Furthermore, we found a relationship between structural complexity and stem and crown size and shape as well as tree growth. Thus, it can be concluded that forest management affected structural complexity of individual Scots pine trees in managed boreal forests, and stem, crown, and growth attributes were identified as drivers of it.
1.Ectomycorrhizal (ECM) roots are evolutionary strategies of plants for effective nutrient uptake under varying abiotic conditions. Formation and morphological differentiations of ECM roots are important strategies in foraging environments. However, little is known on how such strategies mediate the nutrients of the below- and aboveground tissues and the balances among nutrient elements across environmental gradients. 2.We studied the function of ECM symbiosis in Abies faxoniana across its distributional range in Southwest China. The effects of differential ECM strategies, i.e. the contact exploration type, the short-distance exploration type, and the medium-distance exploration type, and root tips functional traits, etc., on root and foliar N and P and N:P ratio were examined across natural environmental gradients. 3.The ECM symbionts preferentially facilitated P uptake in A. faxoniana under both N and P limitations. The uptakes of N and P were primarily promoted by the effectiveness of ECM roots, e.g. ECM root tips per unit biomass, superficial area of ECM root tips, the ratio of living and dead root tips, but negatively related to the ECM proliferations and morphological differentiations. Generally, plant N and P nutrients were always promoted by the contact exploration type, while negatively affected by the short-distance exploration type in A. faxoniana. Root and foliar N and P nutrients were expected to be affected by the medium-distance exploration type in dynamics. Especially, root P limitation could be relieved when the frequency of medium-distance exploration type up to c.15%, whilst root N limitation was strengthen when the frequency of medium-distance exploration type over 20%. 4.We suggest that both below- and above-ground nutritional traits of host tree species could be strongly affected by ECM symbiosis in natural environments. The ECM strategies responding to environmental conditions significantly affect the plant nutrient uptakes and trade-offs. ECM soil exploration types are the great supplementary mechanisms for plant nutrient uptake.
Texas horned lizards (Phrynosoma cornutum) have a number of ways to avoid predation, including camouflage, sharp cranial horns, flattening of the body, and the ability to squirt blood from the eyes. These characteristics and their relatively low survival rates in the wild suggests these lizards are under high predation pressure. These lizards have been declining in much of their eastern range due to increased urbanization, agriculture, and loss of prey species. However, they can be still be found in some small south Texas towns where they can reach densities that are much higher (~50 lizards/ha) than in natural areas (~4-10 lizards/ha). We hypothesized that one reason for the high densities observed in these towns may be due to reduced predation pressure. We used model Texas horned lizards to test whether predation levels were lower in two south Texas towns than on a nearby ranch. We constructed models from urethane foam, a material that is ideal for preserving marks left behind by predators. Models (n = 126) and control pieces of foam (n = 21) were left in the field for 9 days in each location in early and late summer and subsequent predation marks were categorized by predator taxa. We observed significantly more predation attempts on the models than on controls and significantly fewer attempts in town (n = 1) compared to the ranch (n = 60). On the ranch, avian predation attempts appear to be common especially when the models did not match the color of the soil. Our results suggest that human modified environments that have suitable habitat and food resources may provide a refuge for some prey species like horned lizards from predators.