Current Constraints and Future Directions in Estimating Coextinction

Conservation Biology (Impact Factor: 4.17). 01/2010; 24(3):682 - 690. DOI: 10.1111/j.1523-1739.2009.01398.x


Coextinction is a poorly quantified phenomenon, but results of recent modeling suggest high losses to global biodiversity through the loss of dependent species when hosts go extinct. There are critical gaps in coextinction theory, and we outline these in a framework to direct future research toward more accurate estimates of coextinction rates. Specifically, the most critical priorities include acquisition of more accurate host data, including the threat status of host species; acquisition of data on the use of hosts by dependent species across a wide array of localities, habitats, and breadth of both hosts and dependents; development of models that incorporate correlates of nonrandom host and dependent extinctions, such as phylogeny and traits that increase extinction-proneness; and determination of whether dependents are being lost before their hosts and adjusting models accordingly. Without synergistic development of better empirical data and more realistic models to estimate the number of cothreatened species and coextinction rates, the contribution of coextinction to global declines in biodiversity will remain unknown and unmanaged.
Resumen: La coextinción es un fenómeno poco cuantificado, pero los resultados de modelos recientes sugieren grandes pérdidas de biodiversidad local mediante la pérdida de especies dependientes cuando los hospederos se extinguen. Hay vacíos críticos en la teoría de coextincíón, y los delineamos en un marco de referencia para dirigir la investigación futura hacia estimaciones más precisas de las tasas de coextinción. Específicamente, las prioridades más críticas incluyen la obtención de datos más precisos de los hospederos, incluyendo el estatus de amenaza de las especie hospedera; obtención de datos sobre el uso de hospederos por especies dependientes en una amplia gama de localidades, hábitats y amplitud tanto de hospederos como dependientes; desarrollo de modelos que incorporen correlaciones de extinciones no aleatorias de hospederos y dependientes, como la filogenia y atributos que incrementan la susceptibilidad a la extinción; y determinar sí los dependientes se pierden antes que sus hospederos y consecuentemente ajustar los modelos. Sin el desarrollo sinérgico de mejores datos empíricos y modelos más realistas para estimar el número de especies coamenazadas y las tasas de coextinción, la contribución de coextinción a las declinaciones globales de biodiversidad permanecerá desconocida y no podrá ser manejada.

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Available from: Michael Andrew Mccarthy, Sep 11, 2014
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    • "Conversely, the mechanisms and the relevance of the fourth cause, i.e. extinction cascades and/or co-extinctions, have been often underrated, even if their importance has been known for a long time (Stork and Lyal, 1993), and they have been identified by different models as fundamental drivers of species loss (Koh et al., 2004a; Dunn, 2009; Dunn et al., 2009). This subject, however, has recently received increasing attention , and has been thoroughly investigated in a series of studies focusing on the potential role of co-extinctions in biodiversity loss (see, for example, Koh et al., 2004b; Ekl€ of and Ebenman, 2006; Borrvall and Ebenman, 2006; Roopnarine, 2006; Rezende et al., 2007; Nichols et al., 2009; Moir et al., 2010; Sahasrabudhe and Motter, 2011). "
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    ABSTRACT: Human induced ecosystem alterations and climate change are expected to drive several species to extinction. In this context, the attention of public opinion, and hence conservationists' efforts, are often targeted towards species having emotional, recreational and/or economical value. This tendency may result in a high number of extinctions happening unnoticed. Among these, many could involve parasites. Several studies have highlighted various reasons why we should care about this, that go far beyond the fact that parasites are amazingly diverse. A growing corpus of evidence suggests that parasites contribute much to ecosystems both in terms of biomass and services, and the seemingly paradoxical idea that a healthy ecosystem is one rich in parasites is becoming key to the whole concept of parasite conservation. Although various articles have covered different aspects of hosteparasite co-extinctions, I feel that some important conceptual issues still need to be formally addressed. In this review, I will attempt at clarifying some of them, with the aim of providing researchers with a unifying conceptual framework that could help them designing future studies. In doing this, I will try to draw a more clear distinction between the (co-)evolutionary and the ecological dimensions of co-extinction studies, since the ongoing processes that are putting parasites at risk now operate at a scale that is extremely different from the one that has shaped host-parasite networks throughout million years of co-evolution. Moreover, I will emphasize how the complexity of direct and indirect effects of parasites on ecosystems makes it much challenging to identify the mechanisms possibly leading to co-extinction events, and to predict how such events will affect ecosystems in the long run.
    International Journal for Parasitology: Parasites and Wildlife 09/2015; DOI:10.1016/j.ijppaw.2015.08.007
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    • "Our estimates confirmed specialist parasites as the most vulnerable to coextinction. Because parasites ultimately need their hosts for persistence, the number of host species a parasite is associated with is the most crucial parasite trait determining its risk of extinction (Moir et al., 2010). Hence, parasites that exploit different host species have the advantage of being less threatened by extinction, but this comes with the cost of overcoming the physiological and behavioural resistance of different hosts. "
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    ABSTRACT: Amphibians are known as the most threatened vertebrate group. One of the outcomes of a species' extinction is the coextinction of its dependents. Here, we estimate the extinction risk of helminth parasites of South America anurans. Parasite coextinction probabilities were modeled, assuming parasite specificity and host vulnerability to extinction as determinants. Parasite species associated with few hosts were the most prone to extinction, and extinction risk varied amongst helminth species of different taxonomic groups and life cycle complexity. Considering host vulnerability in the model decreased the extinction probability of most parasites species. However, parasite specificity and host vulnerability combined to increase the extinction probabilities of 44% of the helminth species reported in a single anuran species.
    International journal for parasitology 09/2015; DOI:10.1016/j.ijpara.2015.08.010 · 3.87 Impact Factor
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    • "As the transmission of parasites depends in part upon sufficient contact among infected and susceptible hosts (McCallum, Barlow & Hone 2001), extinction processes may decrease the density or abundance of hosts below critical thresholds for parasites to transmit effectively (Deredec & Courchamp 2003; De Castro & Bolker 2005). Although theory suggests that coextinction of hosts and parasites is a common phenomenon, empirical support is scarce and only a few instances of coextinction have been documented (Dunn et al. 2009; Moir et al. 2010). An analysis of parasite richness among wild primates revealed that threatened host species were associated with fewer parasite species compared to non-threatened hosts (Altizer , Nunn & Lindenfors 2007). "
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    ABSTRACT: Host extinction can alter disease transmission dynamics, influence parasite extinction, and ultimately change the nature of host-parasite systems. While theory predicts that single-host parasites are among the parasite species most susceptible to extinction following declines in their hosts, documented parasite extinctions are rare.Using a comparative approach, we investigate how the richness of single-host and multi-host parasites is influenced by extinction risk among ungulate and carnivore hosts. Host-parasite associations for free-living carnivores (order Carnivora) and terrestrial ungulates (orders Perrisodactlya + Cetartiodactlya minus cetaceans) were merged with host trait data and IUCN Red List status to explore the distribution of single-host and multi-host parasites among threatened and non-threatened hosts.We find that threatened ungulates harbour a higher proportion of single-host parasites compared to non-threatened ungulates, which is explained by decreases in the richness of multi-host parasites. However, among carnivores threat status is not a significant predictor of the proportion of single-host parasites, or the richness of single-host or multi-host parasites.The loss of multi-host parasites from threatened ungulates may be explained by decreased cross-species contact as hosts decline and habitats become fragmented. Among carnivores threat status may not be important in predicting patterns of parasite specificity because host decline results in equal losses of both single-host parasites and multi-host parasites through reduction in average population density and frequency of cross-species contact.Our results contrast with current models of parasite coextinction and highlight the need for updated theories that are applicable across host groups and account for both inter and intraspecific contact.This article is protected by copyright. All rights reserved.
    Journal of Animal Ecology 01/2015; 84(4). DOI:10.1111/1365-2656.12342 · 4.50 Impact Factor
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