A dynamical trichotomy for structured populations experiencing positive density-dependence in stochastic environments

Positive density-dependence occurs when individuals experience increased survivorship, growth, or reproduction with increased population densities. Mechanisms leading to these positive relationships include mate limitation, saturating predation risk, and cooperative breeding and foraging. Individuals within these populations may differ in age, size, or geographic location and thereby structure these populations. Here, I study structured population models accounting for positive density-dependence and environmental stochasticity i.e. random fluctuations in the demographic rates of the population. Under an accessibility assumption (roughly, stochastic fluctuations can lead to populations getting small and large), these models are shown to exhibit a dynamical trichotomy: (i) for all initial conditions, the population goes asymptotically extinct with probability one, (ii) for all positive initial conditions, the population persists and asymptotically exhibits unbounded growth, and (iii) for all positive initial conditions, there is a positive probability of asymptotic extinction and a complementary positive probability of unbounded growth. The main results are illustrated with applications to spatially structured populations with an Allee effect and age-structured populations experiencing mate limitation

Discovery-dominance trade-off among widespread invasive ant species.

Ants are among the most problematic invasive species. They displace numerous native species, alter ecosystem processes, and can have negative impacts on agriculture and human health. In part, their success might stem from a departure from the discovery-dominance trade-off that can promote co-existence in native ant communities, that is, invasive ants are thought to be at the same time behaviorally dominant and faster discoverers of resources, compared to native species. However, it has not yet been tested whether similar asymmetries in behavioral dominance, exploration, and recruitment abilities also exist among invasive species. Here, we establish a dominance hierarchy among four of the most problematic invasive ants (Linepithema humile, Lasius neglectus, Wasmannia auropunctata, Pheidole megacephala) that may be able to arrive and establish in the same areas in the future. To assess behavioral dominance, we used confrontation experiments, testing the aggressiveness in individual and group interactions between all species pairs. In addition, to compare discovery efficiency, we tested the species' capacity to locate a food resource in a maze, and the capacity to recruit nestmates to exploit a food resource. The four species differed greatly in their capacity to discover resources and to recruit nestmates and to dominate the other species. Our results are consistent with a discovery-dominance trade-off. The species that showed the highest level of interspecific aggressiveness and dominance during dyadic interactions

The Limits to Sustainability Science: Ecological Constraints or Endless Innovation?

Ecological principles must govern sustainability, yet sustainability science is largely concerned with social-environmental interactions and barely considers physical limits on resource use. Whether it is possible to overcome such limits can be contested, but the issues raised by a macroecological perspective should be a fundamental part of the United Nations Conference on Sustainable Development (Rio+20)

Rare Species Are Valued Big Time

Background: It has recently been postulated that the value humans place on rarity could cause the extinction of rare species. This is because people are willing to pay the high costs of exploiting the last individuals. Many hobbies, such as ecotourism or the keeping of exotic pets may cause this effect – known as the anthropogenic Allee effect. However, the entire theory relies on the insofar undemonstrated assumption that people do value rarity. Methodology/Principal Findings: In order to quantify how much people valued rare species relative to common ones, we created online slideshows of photographs of either rare or common species on an Internet web site. The slideshow with photographs of rare species attracted more visitors, and visitors spent, in general, more time waiting to view it. Conclusions/Significance: We provide evidence that people value rare more than common species. As we did not target consumers of a specific market, this finding suggests that the anthropogenic Allee effect is likely be driven by a large part of the population. Given the substantial participation in our online experiment, we highlight the potential of the world wide web resource as a tool for conservation action. However, the evidence presented here that the general public value rare species, combined with the assumption that anthropogenic Allee effect is operating, implies that conservationists should be prudent when using rarity to promote conservation.Peer reviewe

Colony-colony interactions between highly invasive ants

Among invasive species, ants are a particularly prominent group with enormous impacts on native biodiversity and ecosystem functioning. Globalization and on-going climate change are likely to increase the rate of ant invasions in the future, leading to simultaneous introductions of several highly invasive species within the same area, Here, we investigate pairwise interactions among four highly invasive species, Linepithema humile,Lashis neglectus, Pheidole megacephala and Wasmannia auropunctata, at the whole colony level, using a laboratory set-up. :Each colony consisted of 300 workers and one queen. The number of surviving workers in the competing colonies was recorded daily over 7 weeks. We modelled the survival of each colony during pairwise colony interactions, using a nonlinear model characterizing the survival dynamics of each colony individually. The least dominant species was P. megacephala, which always went extinct. Interactions among the three other species showed more complex dynamics, rendering the outcome of the interactions less predictable. Overall, W auropunctata and L neglectus were the most dominant species. This study shows the importance of scaling up to the colony level in order to gain realism in predicting the outcome of multiple invasions

Using Dynamic Stochastic Modelling to Estimate Population Risk Factors in Infectious Disease: The Example of FIV in 15 Cat Populations

BACKGROUND:In natural cat populations, Feline Immunodeficiency Virus (FIV) is transmitted through bites between individuals. Factors such as the density of cats within the population or the sex-ratio can have potentially strong effects on the frequency of fight between individuals and hence appear as important population risk factors for FIV. METHODOLOGY/PRINCIPAL FINDINGS:To study such population risk factors, we present data on FIV prevalence in 15 cat populations in northeastern France. We investigate five key social factors of cat populations; the density of cats, the sex-ratio, the number of males and the mean age of males and females within the population. We overcome the problem of dependence in the infective status data using sexually-structured dynamic stochastic models. Only the age of males and females had an effect (p = 0.043 and p = 0.02, respectively) on the male-to-female transmission rate. Due to multiple tests, it is even likely that these effects are, in reality, not significant. Finally we show that, in our study area, the data can be explained by a very simple model that does not invoke any risk factor. CONCLUSION:Our conclusion is that, in host-parasite systems in general, fluctuations due to stochasticity in the transmission process are naturally very large and may alone explain a larger part of the variability in observed disease prevalence between populations than previously expected. Finally, we determined confidence intervals for the simple model parameters that can be used to further aid in management of the disease

Understanding Urban Demand for Wild Meat in Vietnam: Implications for Conservation Actions

Vietnam is a significant consumer of wildlife, particularly wild meat, in urban restaurant settings. To meet this demand, poaching of wildlife is widespread, threatening regional and international biodiversity. Previous interventions to tackle illegal and potentially unsustainable consumption of wild meat in Vietnam have generally focused on limiting supply. While critical, they have been impeded by a lack of resources, the presence of increasingly organised criminal networks and corruption. Attention is, therefore, turning to the consumer, but a paucity of research investigating consumer demand for wild meat will impede the creation of effective consumer-centred interventions. Here we used a mixed-methods research approach comprising a hypothetical choice modelling survey and qualitative interviews to explore the drivers of wild meat consumption and consumer preferences among residents of Ho Chi Minh City, Vietnam. Our findings indicate that demand for wild meat is heterogeneous and highly context specific. Wild-sourced, rare, and expensive wild meat-types are eaten by those situated towards the top of the societal hierarchy to convey wealth and status and are commonly consumed in lucrative business contexts. Cheaper, legal and farmed substitutes for wild-sourced meats are also consumed, but typically in more casual consumption or social drinking settings. We explore the implications of our results for current conservation interventions in Vietnam that attempt to tackle illegal and potentially unsustainable trade in and consumption of wild meat and detail how our research informs future consumer-centric conservation actions

Predators reduce extinction risk in noisy metapopulations

Background Spatial structure across fragmented landscapes can enhance regional population persistence by promoting local “rescue effects.” In small, vulnerable populations, where chance or random events between individuals may have disproportionately large effects on species interactions, such local processes are particularly important. However, existing theory often only describes the dynamics of metapopulations at regional scales, neglecting the role of multispecies population dynamics within habitat patches. Findings By coupling analysis across spatial scales we quantified the interaction between local scale population regulation, regional dispersal and noise processes in the dynamics of experimental host-parasitoid metapopulations. We find that increasing community complexity increases negative correlation between local population dynamics. A potential mechanism underpinning this finding was explored using a simple population dynamic model. Conclusions Our results suggest a paradox: parasitism, whilst clearly damaging to hosts at the individual level, reduces extinction risk at the population level

Mechanistic reconciliation of community and invasion ecology

CITATION: Latombe, G., et al. 2021. Mechanistic reconciliation of community and invasion ecology. Ecosphere, 12(2):e03359, doi:10.1002/ecs2.3359.The original publication is available at https://esajournals.onlinelibrary.wiley.comCommunity and invasion ecology have mostly grown independently. There is substantial overlap in the processes captured by different models in the two fields, and various frameworks have been developed to reduce this redundancy and synthesize information content. Despite broad recognition that community and invasion ecology are interconnected, a process‐based framework synthesizing models across these two fields is lacking. Here we review 65 representative community and invasion models and propose a common framework articulated around six processes (dispersal, drift, abiotic interactions, within‐guild interactions, cross‐guild interactions, and genetic changes). The framework is designed to synthesize the content of the two fields, provide a general perspective on their development, and enable their comparison. The application of this framework and of a novel method based on network theory reveals some lack of coherence between the two fields, despite some historical similarities. Community ecology models are characterized by combinations of multiple processes, likely reflecting the search for an overarching theory to explain community assembly and structure, drawing predominantly on interaction processes, but also accounting largely for the other processes. In contrast, most models in invasion ecology invoke fewer processes and focus more on interactions between introduced species and their novel biotic and abiotic environment. The historical dominance of interaction processes and their independent developments in the two fields is also reflected in the lower level of coherence for models involving interactions, compared to models involving dispersal, drift, and genetic changes. It appears that community ecology, with a longer history than invasion ecology, has transitioned from the search for single explanations for patterns observed in nature to investigate how processes may interact mechanistically, thereby generating and testing hypotheses. Our framework paves the way for a similar transition in invasion ecology, to better capture the dynamics of multiple alien species introduced in complex communities. Reciprocally, applying insights from invasion to community ecology will help us understand and predict the future of ecological communities in the Anthropocene, in which human activities are weakening species’ natural boundaries. Ultimately, the successful integration of the two fields could advance a predictive ecology that is urgently required in a rapidly changing world.https://esajournals.onlinelibrary.wiley.com/doi/full/10.1002/ecs2.3359Publisher's versio

Status, trends and future dynamics of biodiversity and ecosystems underpinning nature's contributions to people

Biodiversity at the species and ecosystem levels is currently under multiple threats almost everywhere in the Asia-Pacific region, and in many areas the situation is now critical (well established). Of the various ecosystems, lowland evergreen forests, alpine ecosystems, limestone karsts, inland wetlands, and estuarine and coastal habitats are most threatened (well established). Genetic diversity within species, both wild and domestic, is also decreasing in many cases as a result of decreasing ranges (established but incomplete). In several countries there has been a small increase in the forest cover which is mostly attributed to monoculture forestry plantations and enabling policies of the governments. Forest fires associated with rapid loss of forest cover is leading to enormous environmental and socio-economic loss (well established) {3.2.1; 3.2.2; 3.2.3; 3.2.4; 3.2.5; 3.3.1}. There has been a steady decline in the populations of large vertebrates due to poaching and illegal trade in wildlife parts and products in the Asia-Pacific region (well established). As a result, most of these species now survive only in the best-managed protected areas (well established). Widespread loss of large vertebrates has had a measureable impact on several forest functions and services, including seed dispersal (established but incomplete). Australia has the highest rate of mammal extinction (>10 per cent) of any continent globally. Bird extinctions on individual Pacific islands range from 15.4 per cent to 87.5 per cent for those with good fossil records, and these extinctions have resulted in the loss of many ecological functions previously performed by birds (well established). Besides wildlife, there is a massive regional trade in timber, traditional medicines and other products (well established). Without adequate protection, remediation and proper policies, the current decline in biodiversity and nature's contributions to people on land, in freshwaters, and in the sea will threaten the quality of life of future generations in the Asia-Pacific region {3.2.1.1; 3.2.1.2; 3.2.1.4; 3.2.1.7; 3.2.2.1; 3.3.1} With the current rate of human population growth, expansion of urban industrial environments, transformation of agriculture in favour of high yielding varieties, transforming forests to uniform plantations of oil palm, rubber or timber trees, the biodiversity and nature's contributions to people in the Asia-Pacific region are likely to be adversely affected in the coming decades (well established). It is predicted that most of the biodiversity in the next few decades may be confined to protected areas or in places where the local communities have taken the lead in local level conservation in lieu of economic incentives and equitable compensation by the stake-holders. Unprecedented increase in human population of the Asia-Pacific region has stressed the fragile ecosystems to their limits; while arable cropping has been extended to sites which were not entirely suitable for it, resulting in soil degradation and erosion (well established) {3.2.1.1; 3.2.1.2; 3.2.1.5; 3.2.2.2; 3.2.2.4; 3.3; 3.3.1; 3.3.6; 3.4}. Freshwater ecosystems in the Asia-Pacific region support more than 28 per cent of aquatic and semi-aquatic species but nearly 37 per cent of these species are threatened due to anthropogenic and climatic drivers (well established). Cumulative impacts of global warming and damming of rivers in some of the river basins will have significant negative impacts on fish production and environmental flows (well established). Likewise, degradation of wetlands has had severe negative impacts on migratory waterfowl, fish production and local livelihoods (well established). However, there are scientific data gaps on the current status of biodiversity and nature's contributions to people in most of the river basins, inland wetlands and peatlands of the region {3.2.2.1; 3.2.2.2; 3.2.2.3; 3.2.2.4}. Coastal and marine habitats are likewise threatened due to commercial aquaculture, overfishing, and pollution affecting biodiversity and nature's contributions to people (well established). Detailed analyses of fisheries production in the region have shown severe decline in recent decades. It is projected that if unsustainable fishing practices continue, there could be no exploitable stocks of fish by as early as 2048. This could lead to trophic cascades and collapse of marine ecosystems (established but incomplete). Loss of seagrass beds which forms main diet of several threatened species such as dugong is a major concern (well established). There is a need to conduct systematic and region-wide assessment of fisheries stocks and coastal habitat in the region to aid conservation, management and restoration. {3.1.3.1; 3.2.3.3; 3.2.3.6; 3.2.4.6; 3.4}. Mangrove ecosystems in the Asia-Pacific region are most diverse in the world. They support a rich biodiversity and provide a range of provisioning, regulating and supporting services, which are crucial for the livelihood of local communities (well established). Both mangrove and intertidal habitats form a buffer from siltation for offshore coral reefs protection hence affecting productivity of reefs including seagrass. However, up to 75 per cent of the mangroves have been degraded or converted in recent decades (well established). The conversion of mangroves to aquaculture, rice, oil palm, and other land-use changes is leading to the loss of the buffer between sea and land which can reduce the impact of natural disasters such as cyclones and tsunamis. It is projected that rise in sea level due to global warming would pose the biggest threat to mangroves, thereby affecting nature's contributions to people especially in Bangladesh, Philippines, New Zealand, Viet Nam and China (well established) {3.2.3.1; 3.2.3.2; 3.3.4}. There has been a steady increase in the number, abundance and impacts of invasive alien species in the Asia-Pacific region, negatively affecting native biodiversity, ecosystem functioning and socio-cultural environments (well established). The total annual loss caused by invasive alien species has been estimated at US$35.5 billion in SE Asia and US$9B in Australia. Costs to agriculture due to invasive alien species are likewise immense in the region {3.2.1.1; 3.2.1.2; 3.2.1.4; 3.2.1.5; 3.2.1.6; 3.2.1.7; 3.2.2.1; 3.2.2.2; 3.2.2.3; 3.2.3.6; 3.3.5}. There has been a nearly 30 per cent decline in biocultural diversity in the Asia-Pacific region since the 1970s (well established). Decline of linguistic diversity has been catastrophic in the indigenous Australian and Trans-New Guinean families, as a result of a shifting away from small indigenous languages towards larger, national or regional languages (well established). Linguistic and biological diversity often coincide in the Asia-Pacific region and parallel strategies need to be developed for their conservation. National conservation priorities should take into consideration the bioculturally rich areas that are facing great threats {3.2.5; 3.2.5.2; 3.2.5.4; 3.4}. Protected Area coverage in the Asia-Pacific region has increased substantially since last three decades. Despite this progress, however, at least 75 per cent of Key Biodiversity Areas remain unprotected, suggesting that the region is not on track to conserve areas of particular importance for biodiversity, as called for under Aichi Target 11 (well established). Oceania has the highest overall Protected Area coverage in the region. North-East Asia has the highest proportion of Key Biodiversity Areas covered by Protected Areas, but only 1 per cent of its marine area is protected (well established) {3.2.5.6; 3.2.6; 3.2.6.1}. The Asia-Pacific region has high levels of endemism, and some 25 per cent of the region’s endemic species are facing high extinction risks as per the IUCN Red List. Endemic species in some subregions face an extinction risk as high as 46 per cent of endemic species threatened in South Asia (well established). South-East Asia has the greatest number of threatened species and the fastest increases in extinction risk (Red List Index) in the Asia-Pacific region. North Asian endemic species extinction risk is also higher than the regional average; the high percentage of Data Deficient species (36 per cent) indicates that more research and conservation action are needed for endemic species in this subregion (well established) {3.2.1; 3.2.2; 3.2.6.2; 3.3.4}. Some aspects of biodiversity have recently started to recover in several countries in the Asia-Pacific region (established but incomplete). This recovery has resulted from various changes, including population concentration in cities, increased agricultural production per unit area, increasing conservation awareness among citizens, and the enabling policies of the governments. Future trends of biodiversity in the Asia-Pacific region will largely depend on whether other countries will follow this recovering trajectory by stabilizing land/sea use change, manage their natural resources sustainably, and cooperating with each other in meeting the Aichi Targets and the Sustainable Development Goals {3.2.1.5; 3.2.3.5; 3.3.1; 3.3.3; 3.3.6}. Given that the scientific information on the status and trends of biodiversity and nature's contributions to people is not available uniformly across all ecosystems and habitats in the region, the national governments are encouraged to initiate systematic documentation and monitoring of health of ecosystems and ecosystem flows (established but incomplete). Saving terrestrial fauna especially big mammals and other fauna that require large roaming areas such as Orangutans, proboscis monkey, hornbills, tigers, Sumatran rhinoceros, gaurs and Asian elephants can be done by connecting large tracts of forests with wildlife corridors or through rehabilitation projects; the same goes for coastal and marine, freshwater and other ecosystems in the region {3.2.1.1; 3.2.2.4; 3.3.4; 3.4}