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High prices for rare species can drive large populations extinct: the anthropogenic Allee effect revisited
Abstract and Figures
Consumer demand for plant and animal products threatens many populations with extinction. The anthropogenic Allee effect (AAE) proposes that such extinctions can be caused by prices for wildlife products increasing with species rarity. This price-rarity relationship creates financial incentives to extract the last remaining individuals of a population, despite higher search and harvest costs. The AAE has become a standard approach for conceptualizing the threat of economic markets on endangered species. Despite its potential importance for conservation, AAE theory is based on a simple graphical model with limited analysis of possible population trajectories. By specifying a general class of functions for price-rarity relationships, we provide the first theoretical analysis of AAE models, and show that the classic theory can understate the risk of species extinction. AAE theory proposes that only populations below a critical Allee threshold will go extinct due to increasing price-rarity relationships. Our analysis shows that this threshold can be much higher than the original theory suggests, depending on initial harvest effort. More alarmingly, even species with population sizes above this Allee threshold, for which AAE predicts persistence, can be destined to extinction. Introducing even a minimum price for harvested individuals, close to zero, can cause large populations to cross the classic anthropogenic Allee threshold on a trajectory towards extinction. These results suggest that traditional AAE theory may give a false sense of security when managing large harvested populations.
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... A pioneering model in this field is that of. 16 More recently, variable price models have received more attention with an increasing number of publications, in particular 17,19,[21][22][23][24]29 and in the context of fish infectious disease. 38 Accounting for a variable price is crucial in cases where commercial species are over-exploited, causing a significant decrease in abundance, resulting in a reduced supply with a sustained high demand, leading to an increase in price over prolonged periods. ...
... Therefore, incorporating the Holling type II model into fisheries models highlights these constraints and underscores the importance of appropriate management measures to ensure the long-term sustainability of fish populations beyond this saturation point. In contrast to previous studies 17,19,21,24,29 where the price dynamics depends on the di↵erence between the demand and the supply, through a multiplicative constant, Model (2.1) further assumes that the price equation is proportional to the price itself. This modification in the price equation has a significant implication, as it ensures that the positive domain R 3+ remains positively invariant. ...
We present a bioeconomic fishery model with variable price based on supply and demand. The model considers three variables: resource biomass, fishing e↵ort, and market price. Rapid price changes classify the fishery system as a slow-fast system. Two main cases arise: catastrophic equilibrium (CE) with overexploitation and fish extinction, and a sustainable fishery equilibrium. We aim to determine conditions for maximum sustainable yield by optimizing cost per unit of fishing e↵ort. Additionally, we explore conditions to prevent extinction and restore sustainable fishing. Marine protected areas (MPAs) can restore fish stocks by destabilizing the catastrophic equilibrium and maintaining a stable positive equilibrium. A model incorporating an MPA and fish movement is proposed, suggesting a small carrying capacity-to-surface area ratio in the fishing zone. Optimal total catch can be achieved by selecting the appropriate MPA surface area.
... In order to grow, the initial population must be at a sufficiently high density above this threshold. In the case of a harvested population, a high price of the resource due in particular to its scarcity can also induce an Allee effect [4]. ...
We developed a mathematical model to study the effects of non-pharmaceutical interventions (NPIs) on the dynamics of an epidemic. The level of intervention was assessed as a fraction of the population being isolated and depended on the level of incidence of the epidemic in the population. We performed a mathematical analysis of the model and showed that, depending on the choice of the prevalence-dependent isolation function, it is possible to create new endemic equilibria and to change the stability of the disease-free equilibrium for which the epidemic vanishes. The model was then applied to the case of the COVID-19 pandemic. Several NPI management strategies were considered. In the case of an NPI intensity increasing with the level of infection, it is possible to avoid the initial epidemic peak of great amplitude that would have occurred without intervention and to stabilize the epidemic at a chosen and sufficiently low endemic level. In the case of an NPI intensity decreasing with the level of infection, the epidemic can be driven to extinction by generating an "Allee" effect: when the incidence is below a given level, the epidemic goes extinct whereas, above it, the epidemic will still be able take hold at a lower endemic level. Simulations illustrate that appropriate NPIs could make the COVID-19 vanish relatively fast. We show that, in the context of the COVID-19 pandemic, most countries have not chosen to use the most efficient strategies.
... Several contributions have focused on bioeconomic aspects in fisheries models, [18], and particularly in the case where the price of the resource on the market is variable, [10], [11], [13], [17]. Taking into account a variable price is important in the case of over-exploited commercial species whose abundance can decrease significantly, which causes a decrease in supply with a demand that remains large and finally an increase in the price over long periods. ...
We propose a bio-economic model of a fishery describing the variations of the fish stock, the fishing effort and the price of the resource on the market supposed to depend on supply and demand. The originality of this model comes from taking into account the storage of part of the resource for a certain time before being put up for sale on the market. Taking into account the supposedly fast price dynamics compared to the other mechanisms involved and after integration of the stock equation, the system is reduced to a system of two delayed differential equations. The qualitative analysis of the model is carried out with the search for equilibrium points and the study of their stability. The study shows the existence of a catastrophic equilibrium corresponding to the extinction of the resource and one or two sustainable fishery equilibrium points that can coexist under certain conditions. The model shows that storing part of the resource makes it possible to avoid a catastrophic situation with the extinction of the fish stock and to stabilize the fishery in the long term. The study also shows that the price variation of the resource has a stabilizing effect by avoiding the appearance of periodic solutions associated with a stable limit cycle surrounding a sustainable fishery equilibrium point resulting from a Hopf bifurcation, which is contrary to the case without price variation where this is possible.
... Galapagos giant tortoises are legally protected under CITES; however, rare or endemic species like Galapagos giant tortoises may be especially targeted by IWT because of their scarcity. Species rarity can cause an extinction vortex, the Anthropogenic Allee Effect, in which financial incentives lead to the extraction of the last remaining individuals in the wild (Courchamp et al., 2006), which can threaten even initially large populations (Holden & McDonald-Madden, 2017). Several Galapagos endemic species such as land and marine iguanas (Conolophus subcristatus and Amblyrhynchus cristatus, respectively) and giant tortoises have been targeted by IWT over the past decade with strong demand coming from Europe (Auliya et al., 2016). ...
Illegal Wildlife Trade (IWT) is a cause for global concern as pressure stemming from IWT threatens wild species and can even lead to extinction. Galapagos giant tortoises are a group of threatened species protected under CITES, which forbids their import–export for international trade; however, IWT of this group persists. In this study, we describe the use of two extensive genetic repositories of mitochondrial and nuclear microsatellite markers for Galapagos giant tortoises to identify an unsuspected source of trafficked juvenile tortoises. Our genetic analyses, together with morphological and captive‐born registry data, provide evidence that the smuggled juveniles were from two breeding centers dedicated toward conservation located on the Galapagos islands of San Cristobal and Isabela. This is the first documentation of smuggled tortoises being taken from breeding centers rather than the wild. The findings from our genetic analysis provided key evidence that enabled legal investigation. This case demonstrates the importance of the comprehensive genetic characterization of Galapagos giant tortoises and the suitability of standard genetic markers for identifying the species and islands of origin of trafficked animals. We also discuss the efficacy, adequacy, and reach of existing measures against IWT. Overall, this case illustrates an important application of long‐term and comprehensive genetic repositories of endangered species and the crucial role of collaborations among academic laboratories maintaining those repositories, local practitioners responsible for species protection, and the bodies that implement and enforce antitrafficking regulations.
... So, harvesting models ( [13]- [18]) are getting so much importance in the dynamics of the preypredator system. Allee effect ( [19]- [23]) is another recent trend to work with these types of models. The positive density reliance of populace enlargement at squat densities is known as Allee effect ( [24]- [31]). ...
In this paper, we introduce a prey-predator system with Allee effect in prey where both the prey and predator species are subject to harvesting and exhibit herd behaviour. The new idea of this paper is to consider the Allee effect, herd behaviour and harversing together. Herd behaviour may be proved as a
buffer against environmental obstacles. On the contrary, Allee effect and harvesting together may wash out the population from the system. So, the optimal harvesting policy is significant for the ecosystem concerned with our proposed model. Moreover, taking some hypothetical data, a rigorous numerical illustration and sensitivity analysis of the main parameters are offered here to validate the mathematical findings. To summarise, we can say that our model is an endeavor aiming at the ecological balance in nature.
... This utilization pattern may indicate the anthropogenic Allee effect, which predicts the increasing tendency to exploit the gradually becoming rarer species. This can force a species to an end (Holden and McDonald-Madden 2017). ...
Mandal SK, Rahaman CH. 2022. Perception and application of zootherapy for the management of cattle diseases occurred in northern laterite region of West Bengal, India. Asian J Ethnobiol 5: 12-19. The present study aims to invent the glory of traditional knowledge about zootherapy for livestock diseases in the northern laterite region of West Bengal, India. Semi-structured and open interviews were taken for data collection. Data were analyzed with statistical indices like use mention factor (UM) and use value index (UV). A total of 21 zoological specimens have been recorded. Mammals are the most common species (8 species) used in this region for livestock health care. It has been found that in 57% of cases, endo- & exoskeletal structures like bone, feather, horn, scale, shell, beak, teeth, etc., are used as ethnoveterinary medicine. Four species have been identified as the most frequently used species in the region are Coracias benghalensis (Linnaeus, 1758) (UM=16; UV=0.12), Herpestes javanicus palustris (Ghose, 1965) (UM=12; UV=0.09), Varanus bengalensis (Daudin, 1802) (UM=11; UV=0.08) and Lamellidens marginalis (Lamarck, 1819) (UM=11; UV=0.08). Among the recorded species, more than 50% are enlisted in the IUCN Red List. The present study provides baseline information regarding the depth of ethnozoological knowledge and its current status in the studied area, which will further help frame some conservation strategies for the medicinally important and threatened animal species.
Strong rarity value is the phenomenon that an increase in scarcity of a species (of plants or animals) leads to a price increase which more than compensates increased search costs and lower numbers found or caught. Tipping here is a regime shift moving the system into a low resource-level state from which it is impossible to escape unless measures to restore the resource are taken for a long period of time. We engineer a model in which agents wishing to maximize their limiting average rewards have two choices at every stage of the play, restraint or no-restraint (“overfish”). Overfishing damages the resource, causes tipping and induces scarcity which in turn creates rarity value. We find that Pareto-efficient equilibrium outcomes for very patient agents may require substantial overexploitation of the resource inducing serious threats to its sustainability. However, equilibrium behavior yields a sufficiently rich scheme of outcomes that leave room for viable compromises between ecologically and economically maximalistic policies.
Anecdotal evidence suggests that there is interspecific competition between black‐backed jackal ( Canis mesomelas ) and caracal ( Caracal caracal ) on farmland in South Africa. Home range data were used across both years (1983–2016) and provinces, as well as polynomial interpolation, to quantitatively assess changes in the population of caracal and black‐backed jackal over time. The jackal abundance estimates had low uncertainty, while the caracal data had high uncertainty. A Gaussian model of interspecific competition was developed, using the properties of the Gaussian model and the more reliable jackal abundance data to reduce the uncertainty associated with the caracal data. It was found that caracals have actually declined in South Africa over the past few decades. Caracals are both beneficial to society in terms of trade and other uses and a threat to farmers in terms of livestock predation. To explore the drivers for hunting further, a predator–prey model was developed. The model found that killing for trade is not the main driver for declines in caracal numbers. However, reducing the persecution of caracal on farmland actually stabilises the number of black‐backed jackal, resulting in ‘win–win’ outcomes for both farmers and caracal. A concerted Africa‐wide response to caracal declines is needed.
Understanding drivers of demand for exotic pets may help inform adequate conservation strategies to address unsustainable trade. Here, we used a best-worst scaling approach to understand the variety of preferences and motivations for owning exotic pets. Respondents (316 from 33 countries) preferred exotic pets that were captive-bred, had rare aesthetic features, and were common in the wild and abundant in the market. Species that were at risk of extinction, in short supply, sourced from the wild, and under trade restrictions were the least favoured by respondents. Feelings of care, such as attachment, affection, nurture, as well as curiosity and being passionate about the species, were dominant motivations for pet keepers. Respondents were willing to support the conservation of species in the wild. Our findings highlight that relational dimensions are among the most important aspects influencing decisions to own exotic pets. Certification systems of origin that supports animal welfare and conservation may help consumers support sustainable trade in exotic pet species. However, attention should be paid to challenges throughout the supply chain and not to incentivize consumers' preferences for rare genetic features as this may pose a risk to the conservation of species in the wild. When planning conservation initiatives and policies, considering relational dimensions may provide novel insights to better foster meaningful expressions of care with animals in the wild, as opposed to animals as exotic pets. Fostering care, as a normative human sense of kinship with non-humans, could help channeling "demand for ownership" towards "stewardship re-lations" with nature.
The unsustainable harvest of species for the global wildlife trade is a major cause of vertebrate extinction. Through the Anthropogenic Allee Effect (AAE), overexploitation to extinction can occur when a species’ rarity drives up its market price, enabling profitable harvest of all remaining individuals. Even in the absence of rarity value, however, the harvest of other species can subsidize the overexploitation of a rare species to the point of extinction, a phenomenon termed opportunistic exploitation. These two pathways to extinction have been considered independently, but many traded species experience them simultaneously. In this study, we develop a simple model that incorporates these mechanisms simultaneously and demonstrate that including multiple harvest strategies with market‐based feedbacks fundamentally alters rare species extinction risk and the rate at which overexploitation occurs. As a pertinent case study, we consider the harvest of ground pangolins (Smutsia temminckii). Our results show that pangolin extinction was generally associated with high rarity value, the use of multiple harvest strategies, and the simultaneous harvest of a common species that has a fast life‐history. Pangolin population depletion and short‐term extinction risk were greatest when harvesters used a combination of pursuit and opportunistic (i.e. multi‐species) harvest strategies. Policy implications. Our results suggest that feedbacks between multiple financial incentives to overharvest can exacerbate the risk of extinction of rare species. As a result, continuing to address AAE and opportunistic exploitation as separate extinction pathways may insufficiently capture extinction risk for many exploited species. Criteria for assessing extinction risk or harvest sustainability of exploited species should incorporate multiple drivers of harvest pressure, with an expanded focus on including species with high rarity value that are exploited in multi‐species harvest regimes.
Significance
Many threatened species including elephants, sturgeons, and bluefin tunas are harvested for high-value products. Species can be driven extinct if incentives to harvest do not diminish as populations decline; this occurs if harvest prices rise faster than costs with declining stock. Whereas recent conservation attention for these species has largely focused on market demand, we show—using a theoretical model and an empirical review—that contractions in species’ geographic ranges, which stabilize costs and may be especially common among terrestrial species, might often play a larger role in maintaining harvest incentives. Forces impacting ranges—such as patchy and declining habitats, schooling/herding behavior, and climate change—therefore merit greater attention in assessing overharvesting threats.
The threats of old are still the dominant drivers of current species loss, indicates an analysis of IUCN Red List data by Sean Maxwell and colleagues.
The demand for wildlife products drives an illegal trade estimated to be worth up to $10 billion per year, ranking it amongst the top transnational crimes in terms of value. Orchids are one of the best-selling plants in the legal horticultural trade but are also traded illegally and make up 70% of all species listed by the Convention on the International Trade in Endangered Species (CITES). To study consumer preferences for horticultural orchids we use choice experiments to survey 522 orchid buyers online and at large international orchid shows. Using latent class modelling we show that different groups of consumers in our sample have distinct preferences, and that these groups are based on gender, genera grown, online purchasing and type of grower. Over half of our sample, likely to be buyers of mass-produced orchids, prefer white, multi-flowered plants. Of greater conservation interest were a smaller group consisting of male hobbyist growers who buy their orchids online, and who were willing to pay significantly more for species that are rare in trade. This is the first in-depth study of consumer preferences in the international orchid trade and our findings confirm the importance of rarity as a driver of hobbyist trade. We show that market-research methods are a new tool for conservationists that could provide evidence for more effective conservation of species threatened by trade, especially via campaigns that focus on demand reduction or behaviour change.
Evaluations of wildlife population dynamics have the potential to convey valuable information on the type of pressure affecting a population and could help predict future changes in the population's trajectory. Greater understanding of different patterns of population declines could provide a useful mechanism for assessing decline severity in the wild and identifying those populations that are more likely to exhibit severe declines. We identified 93 incidences of decline within 75 populations of mammalian species using a time-series analysis method. These included linear, quadratic convex (accelerating) declines, exponential concave (decelerating) declines and quadratic concave declines (representing recovering populations). Excluding linear declines left a data set of 85 declines to model the relationship between each decline-curve type and a range of biological, anthropogenic and time-series descriptor explanatory variables. None of the decline-curve types were spatially or phylogenetically clustered. The only characteristic that could be consistently associated with any curve type was the time at which they were more likely to occur within a time series. Quadratic convex declines were more likely to occur at the start of the time series, while recovering curve shapes (quadratic concave declines) were more likely at the end of the time series. Synthesis and applications. The ability to link certain factors with specific decline dynamics across a number of mammalian populations is useful for management purposes as it provides decision-makers with potential triggers upon which to base their conservation actions. We propose that the identification of quadratic convex declines could be used as an early-warning signal of potentially severe decline dynamics. For such a population, increased population monitoring effort should be deployed to diagnose the cause of its decline and avert possible extinctions. Conversely, the presence of a quadratic concave decline suggests that the population has already undergone a period of serious decline but is now in the process of recovery. Such populations will require different types of conservation actions, focussing on enhancing their chances of recovery.
All three surviving elephant species are facing dramatic declines. Poaching driven by consumer demand for ivory in Asia is an important driver of their demise especially in Africa, making their plight a global issue, which has to be addressed by international policy. Michael Gross reports.
Understanding the traits that drive the demand for exotic pets is crucial for improving our ability to prevent the introduction of new invasive species. We investigated the factors influencing species availability within the Australian cagebird trade. We predicted that species price should be an informative indicator of the species abundance in the trade, and that physical attributes, origin of the species, and limitations for free trade and for captive breeding should be important drivers for species price. We investigated the quantitative relationship between species price and these factors using phylogenetically informed models.
The overexploitation of wildlife species is a serious problem in the field of biodiversity conservation. The species subjected to natural Allee effects are even more threatened by exploitation. Moreover, for many wildlife species, their rarity can fuel their exploitation by making them disproportionately desirable and consequently increasing their market price. In this paper, a mathematical model is proposed and analyzed to study how the value that consumers place on rarity can threaten the survival of a species subjected to natural Allee effects. It is assumed that the value of a species increases as its density declines. The analysis of model shows that the increase in the consumers' response to rarity can drive the system to admit Hopf-bifurcation and heteroclinic bifurcation. The occurrence of the heteroclinic cycle indicates that the increase in consumers' response to rarity can cause the extinction of the species. It is found that an increase in the Allee threshold causes a decrease in the threshold value of consumers' response below which extinction is inevitable.
Kenya's government delivered a powerful message against elephant poaching and the illegal ivory trade on 30 April by burning 105 tonnes of ivory, worth up to US$220 million. With stockpile destruction on the rise, it is important to evaluate the impact of this strategy on elephant populations.
Since 1989, 21 countries have burned or crushed 263 tonnes of ivory — most of it (86%) in the past 5 years (see go.nature.com/ivory). However, there is no published evidence so far that these events reduce poaching.
Destroying ivory stockpiles risks a perverse outcome: ivory becomes rarer, fetching higher prices and increasing poaching and illegal stockpiling (see M. 't Sas-Rolfes et al. Pachyderm 55, 62–77; 2014). This has prompted calls by some for a highly controlled legal ivory trade to secure elephant populations (J. F. Walker and D. Stiles Science 328, 1633–1634; 2010) — an option that ivory destruction removes.
It is therefore crucial to track the effects of Kenya's largest-ever ivory burn. Time is short and the stakes are high.
Evaluations of wildlife population dynamics have the potential to convey valuable information on the type of pressure affecting a population and could help predict future changes in the population's trajectory. Greater understanding of different patterns of population declines could provide a useful mechanism for assessing decline severity in the wild and identifying those populations that are more likely to exhibit severe declines.
We identified 93 incidences of decline within 75 populations of mammalian species using a time‐series analysis method. These included linear, quadratic convex (accelerating) declines, exponential concave (decelerating) declines and quadratic concave declines (representing recovering populations). Excluding linear declines left a data set of 85 declines to model the relationship between each decline‐curve type and a range of biological, anthropogenic and time‐series descriptor explanatory variables.
None of the decline‐curve types were spatially or phylogenetically clustered. The only characteristic that could be consistently associated with any curve type was the time at which they were more likely to occur within a time series. Quadratic convex declines were more likely to occur at the start of the time series, while recovering curve shapes (quadratic concave declines) were more likely at the end of the time series.
Synthesis and applications . The ability to link certain factors with specific decline dynamics across a number of mammalian populations is useful for management purposes as it provides decision‐makers with potential triggers upon which to base their conservation actions. We propose that the identification of quadratic convex declines could be used as an early‐warning signal of potentially severe decline dynamics. For such a population, increased population monitoring effort should be deployed to diagnose the cause of its decline and avert possible extinctions. Conversely, the presence of a quadratic concave decline suggests that the population has already undergone a period of serious decline but is now in the process of recovery. Such populations will require different types of conservation actions, focussing on enhancing their chances of recovery.