Coextinction

Abstract: To assess the coextinction of species (the loss of a species upon the loss of another), we present a probabilistic model, scaled with empirical data. The model examines the relationship between coextinction levels (proportion of species extinct) of affiliates and their hosts across a wide range of coevolved interspecific systems: pollinating Ficus wasps and Ficus, parasites and their hosts, butterflies and their larval host plants, and ant butterflies and their host ants. Applying a nomographic method based on mean host specificity (number of host species per affiliate species), we estimate that 6300 affiliate species are “coendangered” with host species currently listed as endangered. Current extinction estimates need to be recalibrated by taking species coextinctions into account.

Abstract: Plants and their pollinators and seed dispersers form complex networks of interdependences. These networks have a well-defined architecture that strongly affects biodiversity maintenance. Using a phylogenetic approach, Rezende et al. show that past evolutionary history of plants and animals partly explains the network patterns. Closely related species tend to play similar roles in the network. As a result, coextinction cascades following a species extinction affect taxonomically related species, resulting in a non-random pruning of the evolutionary tree. From a conservation standpoint, this means that cascades of coextinction may spread across related species, further increasing the erosion of taxonomic diversity. A phylogenetic approach is used to show that past evolutionary history partly explains network patterns that link plants and their pollinators and seed dispersers. Species close in the phylogeny tend to play similar roles in the network. As a result, co-extinction cascades following the extinction of a species affect taxonomically related species, resulting in a non-random pruning of the evolutionary tree. The interactions between plants and their animal pollinators and seed dispersers have moulded much of Earth’s biodiversity1,2,3. Recently, it has been shown that these mutually beneficial interactions form complex networks with a well-defined architecture that may contribute to biodiversity persistence4,5,6,7,8. Little is known, however, about which ecological and evolutionary processes generate these network patterns3,9. Here we use phylogenetic methods10,11 to show that the phylogenetic relationships of species predict the number of interactions they exhibit in more than one-third of the networks, and the identity of the species with which they interact in about half of the networks. As a consequence of the phylogenetic effects on interaction patterns, simulated extinction events tend to trigger coextinction cascades of related species. This results in a non-random pruning of the evolutionary tree12,13 and a more pronounced loss of taxonomic diversity than expected in the absence of a phylogenetic signal. Our results emphasize how the simultaneous consideration of phylogenetic information and network architecture can contribute to our understanding of the structure and fate of species-rich communities.

Abstract: The effects of species declines and extinction on biotic interactions remain poorly understood. The loss of a species is expected to result in the loss of other species that depend on it (coextinction), leading to cascading effects across trophic levels. Such effects are likely to be most severe in mutualistic and parasitic interactions. Indeed, models suggest that coextinction may be the most common form of biodiversity loss. Paradoxically, few historical or contemporary coextinction events have actually been recorded. We review the current knowledge of coextinction by: (i) considering plausible explanations for the discrepancy between predicted and observed coextinction rates; (ii) exploring the potential consequences of coextinctions; (iii) discussing the interactions and synergies between coextinction and other drivers of species loss, particularly climate change; and (iv) suggesting the way forward for understanding the phenomenon of coextinction, which may well be the most insidious threat to global biodiversity.

Abstract: The extinction of a single species is rarely an isolated event. Instead, dependent parasites, commensals, and mutualist partners (affiliates) face the risk of coextinction as their hosts or partners decline and fail. Species interactions in ecological networks can transmit the effects of primary extinctions within and between trophic levels, causing secondary extinctions and extinction cascades. Documenting coextinctions is complicated by ignorance of host specificity, limitations of historical collections, incomplete systematics of affiliate taxa, and lack of experimental studies. Host shifts may reduce the rate of coextinctions, but they are poorly understood. In the absence of better empirical records of coextinctions, statistical models estimate the rates of past and future coextinctions, and based on primary extinctions and interactions among species, network models explore extinction cascades. Models predict and historical evidence reveals that the threat of coextinction is influenced by both host a...