Herbivore Density Research Articles

Disease Outbreak in a Keystone Grazer Population Brings Hope to the Recovery of Macroalgal Forests in a Barren Dominated Island

Macroalgal forests play a key role in shallow temperate rocky reefs worldwide, supporting communities with high productivity and providing several ecosystem services. Sea urchin grazing has been increasingly influencing spatial and temporal variation in algae distributions and it has become the main cause for the loss of these habitats in many coastal areas, causing a phase shift from macroalgae habitats to barren grounds. The low productive barrens often establish as alternative stable states and only a major reduction in sea urchin density can trigger the recovery of macroalgal forests. The present study aims to assess if the 2018 disease outbreak, responsible for a strong reduction in the sea urchinDiadema africanumdensities in Madeira Island, was able to trigger a reverse shift from barren grounds into macroalgae-dominated state. By assessing the diversity and abundance of benthic sessile organisms, macroinvertebrates and fishes before, during and after that particular mass mortality event, we evaluate changes in benthic assemblages and relate them to variations in grazer and herbivore densities. Our results revealed a clear shift from barren state to a macroalgae habitat, with barrens characterized by bare substrate, sessile invertebrate and Crustose Coralline Algae (CCA) disappearing after the mortality event. Overall variations in benthic assemblages was best explained by four taxa (among grazers and herbivores species). However, it was the 2018 demise ofD. africanumand its density reduction that most contributed to the reverse shift from a long stable barren state to a richer benthic assemblage with higher abundance of macroalgae. Despite this recent increase in macroalgae dominated habitats, their stability and persistence in Madeira Island is fragile, since it was triggered by an unpredictable disease outbreak and depends on howD. africanumpopulations will recover. With no control mechanisms, local urchin populations can easily reach the tipping point needed to promote a new shift into barren states. New conservation measures and active restoration are likely required to maintain and promote the local stability of macroalgal forests.

Influence of understory vegetation on soil bacterial communities and nitrogen cycling gene abundance in cool-temperate and sub-alpine forests along an elevational gradient

Understanding how the community structures and functions of soil microbes respond to environmental changes is essential for predicting the dynamics of ecosystem functions. Elevational gradients are an ideal setting for “natural experiments” on the relationships between soil microbes and environmental factors. However, little is known about elevational patterns of soil microbial functions and their interactions with aboveground vegetation. We examined community structures and nitrogen cycling gene abundance of soil bacteria in 20 vegetation survey quadrats in cool-temperate and sub-alpine forests along an elevational gradient (1050–2000 m above sea level) in central Japan. The diversity of soil bacterial communities was investigated based on terminal restriction fragment length polymorphisms (T-RFLP) in the 16S rRNA gene. The abundance of soil bacteria and key functional groups involved in nitrogen cycling was determined by quantifying the 16S rRNA and bacterial genes related to nitrogen fixation (nifH), ammonia oxidation (amoA), and denitrification (nosZ). The terminal restriction fragment (T-RF) richness of soil bacteria showed no relationship with elevation, but was negatively associated with soil nitrate-nitrogen and the species richness of understory vegetation. The abundance of all bacteria and nitrogen functional groups showed hump-shaped relationships with elevation, and was positively associated with soil water content and understory stem density. These results highlight that community structures and nitrogen cycling gene abundance of soil microbes along the elevational gradient can be explained by soil properties associated with understory vegetation. This suggests that vegetation decline caused by environmental changes, such as climate warming, land use change, and increased herbivore density, may deteriorate soil ecosystem functions through aboveground–belowground interactions.

Multi-scale mosaics in top-down pest control by ants from natural coffee forests to plantations.

While top-down control plays an important role in shaping both natural and agricultural food webs, we lack insights into how top-down control effects vary across spatial scales. We used a multi-scale survey of top-down control of coffee pests and diseases by arboreal ants to examine if colony location creates a small-scale mosaic in top-down control around trees and if the strength of that control varies between sites at the landscape scale. We investigated pest and disease levels on coffee shrubs at different distances from shade trees with and without a Crematogaster spp. ant colony in 59 sites along a coffee management intensity gradient in southwestern Ethiopia. Within sites, ants significantly suppressed herbivory and coffee leaf rust at distances less than 10m from nesting trees. Top-down control varied between sites, with stronger top-down control of free-feeding herbivory near ant colonies at sites with lower management intensity and stronger top-down control of a skeletonizer at sites with higher canopy cover. We conclude that the strength of top-down control by ants is highly heterogeneous across spatial scales, as a consequence of the biology of the predator at the small scale and herbivore density or changes in herbivore-ant interactions at the landscape scale.

An exotic herbivore reinforces competition between exotic and native plants

Abstract Despite increasing evidence that herbivore‐mediated indirect effects play a major role in plant competition, it is unclear how and when they contribute to plant invasiveness. The outcomes of herbivore‐mediated indirect effects are primarily dependent on the environment and have complex interactions with the direct interactions between plants. We evaluated the herbivore‐mediated indirect effects of Solidago altissima (Asteraceae) on other co‐occurring native Asteraceae species at multiple sites in a native range [the United States (US)] and in an introduced range (Japan) using common garden experiments. We examined the effect of S. altissima on herbivore damage, above‐ground vegetative and reproductive traits of the co‐occurring Asteraceae species at sites with different densities of a herbivore, the lace bug, Corythucha marmorata, which is native to the US and introduced in Japan. We observed increased lace bug herbivory in plants grown with S. altissima in Japan but decreased lace bug herbivory in the US. We did not find consistent effect of S. altissima on aboveground vegetative production of co‐occurring plants in either ranges. Flower production decreased in plants grown with S. altissima in Japan because of both direct competition and increased herbivory. Direct competition and apparent competition via lace bug herbivory interacted to produce a strong negative effect of S. altissima on co‐occurring plants only in Japan. Synthesis. The findings imply that evolutionary history and the local environment jointly affect herbivore‐mediated indirect effects, which play a large role in shaping the pattern of herbivory and plant competition. Another implication of our results is that exotic herbivores may reinforce the negative effects of exotic plants on native plants under high herbivore density environments.

The link between climate change and biodiversity of lacustrine inhabitants and terrestrial plant communities of the Uvs Nuur Basin (Mongolia) during the last three millennia

The paper is focused on changes in biodiversity, the environment, and human activity in the Uvs Nuur Basin during the last three millennia based on biological and geochemical proxies from the lake Bayan Nuur. Regions with high biodiversity and relatively low anthropogenic pressures are typically the most vulnerable to both climate change and human activities. One such area is the Uvs Nuur Basin located on the north of the Great Lake Depression of Mongolia. The main objective of this study is to assess changes in the past biodiversity of the lake’s microflora and microfauna, and surrounding vegetation biodiversity in the Uvs Nuur Basin, and to determine the main drivers of diversity change. Based on the analysis of pollen and chironomids we conclude that the most humid and afforested phase was between 1400 and 1800 CE. We assume that the Little Ice Age in the Uvs Nuur Basin was humid with mean annual precipitation ca. 305 mm/year and mean July temperature about 13°C. Conversely, the warmest and most arid period was between 650 and 1350 CE with mean annual precipitation ca. 280 mm/year and mean July temperature of about 16°C, attributed to the Medieval Warm Period. The biodiversity of terrestrial plants, chironomids, and Cladocera positive react to changes in annual precipitation and July temperature, whereas diatoms do not correlate directly to the climatic factors. The diversity and the evenness of plants are strongly correlated with the change in the leading biomes. The calculated species turnover suggests no significant changes in plant and Cladocera taxa composition, but significant changes in diatom and chironomid communities. This may be explained by the instability of lake ecology due to the fluctuation of the salinity and acidity of the water. An additional aim was to assess if dung fungi in lacustrine sediments reflect changes in human population density around the lake. We found that neither historical sources of human presence nor the influx of coprophilous fungi are correlated with the inferred climate changes. Coprophilous fungi can be used as individual or additional sources of assessment for the peopling and human-related herbivore density including overgrazing of the studied area.

Land-use intensity affects the potential for apparent competition within and between habitats.

Arthropod communities dwelling in adjacent habitats are able to impact one another via shared natural enemies. In agricultural landscapes, drastic differences in resource availability between crop and non-crop habitats cause variation in insect herbivore densities over short distances, potentially driving inter-habitat effects. Moreover, the composition of the landscape in which the habitats are embedded likely affects realised attack rates from natural enemies via impacts on local arthropod community structure. Here, we examine indirect effects between herbivore species within and between habitat types by calculating the potential for apparent competition between multiple populations. Firstly, we aim to determine how disparities in resource availability impact the strength of the potential for apparent competition occurring between habitats, secondly to examine the impact of landscape composition upon these effects, and finally to couch these observations in reality by investigating the link between the potential for apparent competition and realised attack rates. We used DNA metabarcoding to characterise host-parasitoid interactions within two habitat types (with divergent nutrient inputs) at 11 locations with variable landscape composition within an agroecosystem context. We then used these interaction networks to estimate the potential for apparent competition between each host pair and to compare expected versus realised attack rates across the system. Shared natural enemies were found to structure host herbivore communities within and across habitat boundaries. The size of this effect was related to the resource availability of habitats, such that the habitat with high nutrient input exerted a stronger effect. The overall potential for apparent competition declined with increasing land-use intensity in the surrounding landscape and exhibited a discernible impact on realised attack rates upon herbivore species. Thus, our results suggest that increasing the proportion of perennial habitat in agroecosystems could increase the prevalence of indirect effects such as apparent competition among insect herbivore communities, potentially leading to enhanced population regulation via increased attack rates from natural enemies like parasitoid wasps.

Neighbourhood effect of faba bean (Vicia faba L.) on density of vegetation-dwelling natural biocontrol agents in winter wheat

Legume crops such as faba bean (Vicia faba L.) have been underrepresented in conventional cropping systems in Europe for decades for economic reasons, even though faba bean is a native crop and suitable to diversify local cropping systems. While the environmental benefits that go along with faba bean cropping are well established, there is a gap of knowledge on the effects faba bean may have on biodiversity and associated ecosystem services, such as natural biocontrol in agricultural landscapes.The aim of the present field study was to quantify neighbourhood effects of faba bean on densities of vegetation- dwelling natural biocontrol agents and herbivores in adjacent winter wheat. Densities of predators, herbivores, parasitized aphids (mummies) and leaf damage by the cereal leaf beetle (CLB) were assessed by repeated visual counts in conventionally managed winter wheat crops. In winter wheat adjacent to faba bean, total predator density was higher than in wheat adjacent to winter wheat, independent of the observation period. This effect was not reflected in the predator-prey ratio though. The total density of mummies and parasitism rate were not affected by the neighbouring faba bean crop. Predator density decreased towards the field centre. CLB leaf damage and yield were not affected by the neighbouring crop. All densities were affected by the observation period. The effects were measurable in spite of the external management such as insecticide application, which had a negative effect on both predator and herbivore densities. The present study sheds first light on faba bean effects on natural biocontrol agents in conventionally managed agro-ecosystems. While few, effects were measurable, which shows the need for further research on the association of faba bean cropping with the ecosystem service natural biocontrol.

Indirect plant defenses: volatile organic compounds and extrafloral nectar

Indirect plant defense is an important component in regulating population dynamics and the structure of numerous communities in different ecosystems. These defenses mainly involve the emission of volatile organic compounds (VOCs) induced after damage by an herbivore. VOCs can play several ecological roles, such as help natural enemies locate prey or hosts, attract or repel other herbivores, mediate communication between neighboring plants and among different parts of the same plant, and affect the behavior of pollinators and seed dispersers. In addition to VOCs, some plants produce extrafloral nectar, which can enhance plant defense, by attracting, retaining, and increasing the efficiency of some natural enemies; however, among the associated costs, these compounds can attract other herbivorous species and exclude some natural enemies due to competition. Many factors can influence the production of indirect defenses by plants, such as the individual species, life stage, density of herbivores, age, abiotic factors, as well as the association of plants with symbiotic microorganisms. The potential of indirect plant defenses to reduce herbivory and increase the plant fitness has been well demonstrated. Indirect plant defenses may have ecological costs but can express phenotypic plasticity, as plants can reduce or increase the production of defenses according to the associated herbivory rate. Such variable expression of characteristics provides a barrier against the evolution of resistance by the associated herbivores. In this article, we intend to provide a review on volatile organic compounds and extrafloral nectar as indirect plant defenses, including some costs and benefits of these defense mechanisms.

Influence of Vineyard Inter-Row Groundcover Vegetation Management on Arthropod Assemblages in the Vineyards of North-Eastern Italy.

Simple SummaryHabitat simplification and use of pesticides in vineyard agro-ecosystems simplified arthropod communities, reducing natural pest control. In this context, habitat management practices could be useful strategies to provide fundamental sources for sustaining natural enemies. The effects of habitat management practices on pests and beneficial arthropods were evaluated in vineyards of North-eastern Italy through different field experiments. We reduced mowing frequency of inter-row spontaneous grasses, compared different timing of mowing of a green manure mixture, and different green manure mixtures. The abundance of key natural enemies (e.g., predatory mites, parasitic wasps and spiders) and some grapevine leafhoppers increased when the grass mowing frequency was reduced. Many beneficial arthropods increased in numbers in organic vineyards. Late mowing of green manure favored spiders and parasitic wasps but not herbivores associated with grapevines. The experiments on the comparison of green manure mixtures did not significantly affect the arthropod communities. Groundcover management practices could enhance beneficial arthropod abundance, but the adoption of this practice should be carefully evaluated when pests occur. In this study, the effects of habitat management practices on both pests and beneficial arthropods were evaluated in vineyards of North-eastern Italy through different field experiments: (1) mowing of inter-row spontaneous grasses in conventional and organic vineyards, (2) different timing of mowing of a green manure mixture, and (3) comparing different green manure mixtures. The first experiment followed a split-plot design, while randomized block design was used in the second and third experiment. In each experiment arthropods were sampled using different methods: leaf sampling, beating and sweep net sampling. Non-mowed spontaneous grasses in inter-rows of vineyards favored the abundance of natural enemies (e.g., predatory mites, parasitic wasps and spiders), and sometimes grapevine leafhoppers. Many arthropod species were recorded in higher numbers in organic vineyards. Late mowing of green manure favored beneficial arthropods (e.g., spiders and parasitic wasps), while it did not influence herbivore density. Groundcover management practices, aimed at increasing plant biodiversity in vineyards, could be a useful tool to enhance beneficial arthropod abundance, although the adoption of this practice should be carefully evaluated when pests occur. Semi-natural areas can contribute to create a more pest-stable agro-ecosystem and should be integrated with appropriate ecological infrastructures surrounding vineyards.

Effects of herbivory by the urchin Diadema antillarum on early restoration success of the coral Acropora cervicornis in the central Caribbean

In an era of coral reef decline, coral restoration is receiving increasing attention, with many recent developments in culture and transplant techniques. However, how the ecological processes operating on coral reefs influence the success of restoration efforts remains largely unexplored, particularly during the first months after outplanting which are considered crucial for colony survival. Herbivory is a key process well-known to maintain a coral-dominated state, and in the Caribbean Sea, the long-spine urchin Diadema antillarum is thought to aid coral success by removing algae from seafloor substrate that might otherwise outcompete coral outplants. In this study, we conducted a three-month manipulative experiment in southeastern Dominican Republic to test the effect of Diadema antillarum density on percent living tissue and growth rate of outplanted fragments of the critically endangered coral species Acropora cervicornis. Increasing herbivore density had no significant effect on coral survival or growth but did increase the percent of living tissue when urchin abundance was 3× ambient levels. The greatest growth and survival outcomes were instead related to the initial size of the outplanted coral and were reduced through predation by the fireworm Hermodice carunculata. Our results highlight the potential importance of considering ecological processes like herbivory and predation to maximize the success of ecological restoration.

Herbivores reduce seedling recruitment in alpine plant communities

Through changes in climate and other environmental factors, alpine tundra ecosystems are subject to increased cover of erect shrubs, reduced predictability of rodent dynamics and changes in wild and domesticated herbivore densities. To predict the dynamics of these ecosystems, we need to understand how these simultaneous changes affect alpine vegetation. In the long term, vegetation dynamics may depend critically on seedling recruitment. To study drivers of alpine plant seedling recruitment, we set up a field experiment where we manipulated the opportunity for plant–plant interactions through vegetation removal and introduction of willow transplants, the occurrence of herbivory through caging of plots, and then sowed 14 species into the plots. We replicated the experiment in three common alpine vegetation types (heath, meadow andSalixshrubland) and recorded seedling emergence and survival over five years. Strong effects of vegetation removal and substantial differences in recruitment among dominant vegetation types suggested important effects of local vegetation on the recruitment success of vascular‐plant seedlings. Similarly, herbivore exclusion had strong positive effects on recruitment success. This effect arose primarily via reduced seedling mortality in plots from which herbivores had been experimentally excluded and became noticeably stronger over time. In contrast, we detected no consistent effects of experimental willow shrub introduction on seedling recruitment. These results demonstrate that large and small herbivores can affect alpine plant seedling recruitment negatively by trampling and feeding on seedlings. Importantly, the effects became stronger over time, suggesting that effects of herbivory on seedling recruitment accumulates over time and may relate to recruitment phases beyond initial seedling emergence.

Sea Urchins Play an Increasingly Important Role for Coral Resilience Across Reefs in Taiwan

Herbivores are an important functional group that control algae, create new space, and promote recruitment for coral recovery. However, on many coral reefs, overfishing has greatly decreased the density of herbivores, especially fishes and gastropods, impairing coral resilience. On such overfished reefs, remnant herbivores that are not target species of local fisheries, e.g., sea urchins, are expected to play an increasingly important role, yet few studies, except for those in the Caribbean and Kenya have examined non-fish herbivores in relation to coral resilience. Here, we conducted field surveys at 30 sites along three coral reefs in Taiwan between 2016 and 2017, to examine the relative importance of six key factors for coral resilience: herbivore abundance (fishes, gastropods, sea urchins), coral cover, macroalgal cover, habitat complexity, water depth, and wave exposure. The density of juvenile coral was used as a proxy of coral resilience. Diadematid sea urchins (Echinothrix spp. and Diadema spp.) dominated most sites (19 of 30 sites) and multivariable regression models showed sea urchin density as the best positive predictor of coral juvenile density. The results elucidated the increasing role diadematid sea urchins play as remnant herbivores on overfished coral reefs in Taiwan. Given that overfishing is a widespread issue, this phenomenon may be occurring globally. More studies are needed to examine the role of remnant, but often ignored, sea urchin herbivory on coral resilience. Reef managers should consider monitoring locally remnant herbivores and incorporating them into management strategies.

Invasive predator disrupts link between predator evenness and herbivore suppression

Biodiversity provided by non-crop plants has long been thought to strengthen conservation biological control by providing food and habitat for natural enemies. More recently, greater evenness among natural enemies has also been suggested to promote strong top-down control, but habitat characteristics and management strategies that promote or disrupt evenness among predators remain unclear. We examined effects of non-crop plants, and the activity density of the invasive intraguild predator Pterostichus melanarius (Coleoptera: Carabidae), on evenness among predators of the crucifer flea beetle (Phyllotreta cruciferae; Coleoptera: Chrysomelidae). We sampled ground-active predators, flea beetles, and in-row coverage of non-crop vegetation on 52 Brassica fields across three US states, and used structural equation models to evaluate direct and indirect, predator-mediated effects of non-crop plant cover on pest abundance. We found that non-crop plant cover and high evenness among predators associated with higher predator activity and indirectly with lower herbivore densities, consistent with stronger biocontrol. However, non-crop plants attracted the invader P. melanarius. In turn, P. melanarius linked with lower evenness among other ground-active predators, while showing no direct effect on flea beetles, suggesting potential disruptive interference by P. melanarius. While non-crop plants are widely known to attract diverse predators, it may be difficult for growers to manipulate plant communities that increase enemy evenness and promote natural pest control if intraguild predators commonly benefit from these resources as well. More generally, our results suggest a need for closer examination of role of predator-predator interactions in relationships between plant diversity and biological control across agroecosystems.

Differential herbivore occupancy of fire-manipulated savannas in the Satara region of the Kruger National Park, South Africa

The Kruger National Park’s (KNP) long-running experimental burn plots (EBPs) have a history of research projects, which improve the understanding of fire in savanna ecosystems. Using data from KNP’s aerial censuses (2005–2016) and in situ dung count data (2008–2017), this study assessed (1) herbivore densities on the Satara, N’Wanetsi and Marheya EBPs, on annual, triennial and no-burn treatments and across pre-, during and post-drought climate conditions; (2) herbivore densities of these EBPs relative to their non-manipulated surroundings and (3) the extent to which distance to water and rainfall influence ungulate densities. The results revealed that herbivore mean density differed significantly between the three EBPs of Satara and across their fire treatments. N’Wanetsi showed the highest density (0.30 animals/ha), whilst the lowest was found at Marheya (0.12 animals/ha). Overall, pre-drought density was higher on the annual plots (0.56 animals/ha), whilst higher post-drought density was evidenced on the triennial plots (0.80 animals/ha). On average, there were significantly higher herbivore densities on the EBPs (2.54 animals/ha) compared to the surrounding matrix at the larger scales of the Satara management section (0.15 animals/ha) and the central KNP (0.18 animals/ha). A positive correlation between herbivore mean density estimate and distance to water was shown. However, grazer mean density across fire treatments was strongly correlated to rainfall.Conservation implications: Given the variation in fire regimes and their application, and the non-uniform and elevated herbivore densities of the EBPs, inferences from the EBPs cannot be made to the larger KNP. The trials should rather be viewed as an isolated, fire herbivory experiment. It is also recommended to align the experiment with South African National Parks’ mandate by including biodiversity parameters like small mammals and insects in the monitoring of the plots.

Global impacts of fertilization and herbivore removal on soil net nitrogen mineralization are modulated by local climate and soil properties.

Soil nitrogen (N) availability is critical for grassland functioning. However, human activities have increased the supply of biologically limiting nutrients, and changed the density and identity of mammalian herbivores. These anthropogenic changes may alter net soil N mineralization (soil net Nmin ), that is, the net balance between N mineralization and immobilization, which could severely impact grassland structure and functioning. Yet, to date, little is known about how fertilization and herbivore removal individually, or jointly, affect soil net Nmin across a wide range of grasslands that vary in soil and climatic properties. Here we collected data from 22 grasslands on five continents, all part of a globally replicated experiment, to assess how fertilization and herbivore removal affected potential (laboratory-based) and realized (field-based) soil net Nmin . Herbivore removal in the absence of fertilization did not alter potential and realized soil net Nmin . However, fertilization alone and in combination with herbivore removal consistently increased potential soil net Nmin. Realized soil net Nmin , in contrast, significantly decreased in fertilized plots where herbivores were removed. Treatment effects on potential and realized soil net Nmin were contingent on site-specific soil and climatic properties. Fertilization effects on potential soil net Nmin were larger at sites with higher mean annual precipitation (MAP) and temperature of the wettest quarter (T.q.wet). Reciprocally, realized soil net Nmin declined most strongly with fertilization and herbivore removal at sites with lower MAP and higher T.q.wet. In summary, our findings show that anthropogenic nutrient enrichment, herbivore exclusion and alterations in future climatic conditions can negatively impact soil net Nmin across global grasslands under realistic field conditions. This is an important context-dependent knowledge for grassland management worldwide.

Response of Kalahari vegetation to seasonal climate and herbivory: Results of 15 years of vegetation monitoring

AbstractQuestionsThe arid Kalahari is prone to desertification as a result of climate change and/or land use. We analysed the effects of climatic variables and game herbivory on the vegetation composition to answer the question of how different life‐form types respond to climate, browsers and grazers as drivers of vegetation change.LocationThe study was situated in the arid savanna of the South African Kalahari.MethodsVegetation monitoring was conducted on 20 randomly selected permanent plots (100 m2) within a biodiversity observatory. For each plot, individuals per species (abundance) were counted annually and grouped into eight life‐form types (annual and perennial graminoid and annual and perennial forb, geophyte, dwarf shrub, large shrub and tree). We ran generalised linear mixed models (GLMM) with abundance per life‐form type as response variable and a seasonal drought index (Standardised Precipitation–Evapotranspiration Index [SPEI]), total annual rainfall, year, density of large game and springbok as fixed effects, plot as random effect and year as random slope.ResultsSeasonal SPEI and density of large game and springbok had the strongest effect on abundance per life‐form type. Annual rainfall did not show any effect. The grazing large game had positive effects on the abundance of herbaceous life forms and dwarf shrubs. The predominantly browsing springbok had negative effects on perennial forbs, dwarf shrubs and trees. Directional trends in abundance per life form over time (increase of annual and decrease of perennial graminoids and forbs, increase of large shrubs) and decrease of total annual cover suggest early stages of vegetation degradation and shrub encroachment in response to both herbivory and climate.ConclusionsOur study showed that studies aimed at understanding the dynamics of arid systems should include both variance of intra‐annual climatic conditions and herbivore density as environmental drivers, related to abundance per life‐form/strategy type to reveal their specific responses to the environment.

Competitor densities, habitat, and weather: effects on interspecific interactions between wild deer species.

There is a growing interest on the potential interplay between weather, habitat, and interspecific competition on population dynamics of wild herbivores. Favorable environmental conditions may buffer the negative effects of competition; conversely, competition may be expected to be stronger under harsh environmental conditions. We investigated relationships between competitor abundance, weather, and habitat cover on density and local distribution of a medium‐sized herbivore, the roe deer Capreolus capreolus, as well as its spatial overlap with fallow deer Dama dama in a Mediterranean protected area. Over 11 years (2007–2017), roe deer density was not affected by spring–summer rainfall in the previous year and decreased with increasing density of fallow deer in the previous year. Hence, over the considered temporal scale, results supported a major role of competition over weather in influencing population trends of roe deer. At a finer spatial scale, roe deer occupancy was negatively affected by local abundance of fallow deer, especially in “poorer” habitats. We found a slight support for a positive effect of fallow deer density on interspecific spatial overlap. Moreover, fine‐scale spatial overlap between deer species increased with decreasing rainfall in spring–summer. Fallow deer were introduced to our study area in historical times and their role as superior competitors over roe deer has been found also in other study areas. We suggest a potential role of harsh weather conditions during the growing season of vegetation (i.e. scarce rainfall) in triggering the potential for ecological overlap, emphasizing the negative effects of interspecific competition.

Kelp forests

Vergés and Campbell introduce the kelp forest ecosystem.

Unravelling effects of grazing intensity on genetic diversity and fitness of desert vegetation

Biodiversity conservation focuses on species and/or populations, but preserving genetic diversity and structure has received limited attention and even less maintaining species evolutionary potential over generations. Genetic diversity is an essential component of biodiversity enabling species’ persistence, particularly under disturbances. Via sexual reproduction genetic diversity is transmitted across generations and greater outcrossing in parental populations will lead to greater genetic diversity in their offspring. Grazing by exotic large herbivores is one of the main disturbances driving biodiversity loss threatening rangelands sustainability worldwide. We investigated grazing effects on fitness and genetic diversity of parental and offspring cohorts of Prosopis alpataco from Patagonian Monte Desert. We collected fresh leaves and seeds from 10 independent rangelands with different herbivore density, forming a grazing gradient, and estimated genetic parameters from allele frequencies using isoenzymes. We recorded plant size, seed weight, seed set, seedling emergence and mortality as proxies of plant fitness. Applying regression models and path analysis (D-separation) approaches we observed that increasing grazing reduced seed set and seedling emergence, and significantly increased seedling mortality. Parental and offspring suffered from inbreeding. Moreover, we found genetic diversity loss throughout cohorts in all rangelands, however, this loss was relatively lower at intermediate grazing intensities. The introduction of large herbivores in unmanaged rangelands affected vegetation structure, jeopardizing their evolutionary potential and system sustainability. Therefore, natural revegetation may be compromised by aggravated genetic diversity losses along generations that might be deepened in drylands under forecasted climate change. This highlights the importance of evaluating and conserving genetic diversity.

Terrestrial threats dominate the waterbird landscape of fear in a savannah pan wetland system

Natural or anthropogenic disturbances (stimuli that trigger a behavioural response from animals) can have direct consequences on fitness and population trends. This study aimed at investigating the relative influence of three types of disturbances (mammalian herbivores, terrestrial threats from ground predators and aerial threats) on the responses by waterbirds at waterpans in Hwange National Park (HNP, Zimbabwe) and adjacent land uses. Thirteen waterpans were monitored during daylight hours between years 2015 and 2017 and responses of waterbirds to the three forms of disturbances were recorded. Logistic regressions revealed that the likelihood of responding was highest after terrestrial threats; with individuals/groups that were initially engaged in non-feeding activities that allowed vigilance, responding the most. Wildfowl species spent significantly longer time flying (compared to waders and generalists), more so in communal areas (CAs) than HNP, and after terrestrial threats compared to aerial threats and herbivore disturbances. We did not find any differences in probability of responding across land uses probably because there is less human disturbance in HNP, but predation risk is high. Further, even though there are less terrestrial predators in CAs, domestic dogs may be maintaining the stimuli. We conclude that terrestrial threats are least tolerated, with species most susceptible to human predation (i.e. wildfowl) losing more time avoiding them. Interestingly, only acute aerial threats induced departure from waterpans. Our findings have a direct implication for waterbird conservation as herbivore and human density in this area are currently increasing.