Do asynchronies in extinction debt affect the structure of trophic networks? A case study of antagonistic butterfly larvae–plant networks

Guardiola M., Stefanescu C., Rod F., Pino J. (2018) Do asynchronies in extinction debt affect the structure of trophic networks? A case study of antagonistic butterfly larvae–plant networks. Oikos. 127: 803-813.
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Doi: 10.1111/oik.04536

Resum:

Habitat loss and fragmentation affect species richness in fragmented habitats and can lead to immediate or time-delayed species extinctions. Asynchronies in extinction and extinction debt between interacting species may have severe effects on ecological networks. However, these effects remain largely unknown. We evaluated the effects of habitat patch and landscape changes on antagonistic butterfly larvae–plant trophic networks in Mediterranean grasslands in which previous studies had shown the existence of extinction debt in plants but not in butterflies. We sampled current species richness of habitat-specialist and generalist butterflies and vascular plants in 26 grasslands. We assessed the direct effects of historical and current patch and landscape characteristics on species richness and on butterfly larvae–plant trophic network metrics and robustness. Although positive species- and interactions–area relationships were found in all networks, structure and robustness was only affected by patch and landscape changes in networks involving the subset of butterfly specialists. Larger patches had more species (butterflies and host plants) and interactions but also more compartments, which decreased network connectance but increased network stability. Moreover, most likely due to the rescue effect, patch connectivity increased host-plant species (but not butterfly) richness and total links, and network robustness in specialist networks. On the other hand, patch area loss decreased robustness in specialist butterfly larvae–plant networks and made them more prone to collapse against host plant extinctions. Finally, in all butterfly larvae–plant networks we also detected a past patch and landscape effect on network asymmetry, which indicates that there were different extinction rates and extinction debts for butterflies and host plants. We conclude that asynchronies in extinction and extinction debt in butterfly–plant networks provoked by patch and landscape changes caused changes in species richness and network links in all networks, as well as changes in network structure and robustness in specialist networks. © 2017 The Authors

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General declines in Mediterranean butterflies over the last two decades are modulated by species traits

Melero Y., Stefanescu C., Pino J. (2016) General declines in Mediterranean butterflies over the last two decades are modulated by species traits. Biological Conservation. 201: 336-342.
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Doi: 10.1016/j.biocon.2016.07.029

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Species' responses to environmental changes are highly idiosyncratic and context-dependent. Although intrinsic traits (i.e. those that define species niches) may play a key role, little empirical evidence exists regarding their relationship to demographic responses. We used data for 66 butterfly species representing five ecological and two life-history traits to study the effect these factors have on population growth rates and variations in populations. Using a novel methodological approach, we provide here improved estimates of population change. Our results reveal declines in 70% and increases in 23% of the studied species, clear evidence of more serious population declines in Catalan butterflies than those that have previously been reported. Declines were associated with species' degree of habitat specialisation and the number of generations. For all species, fluctuations were greater within than between years and, on average, the latter was 1.5 times greater. Our results indicated that habitat specialists and multivoltine species are more likely to suffer severe annual fluctuations in population abundance; and that multivoltine species and extreme larval specialists had the most marked fluctuations within seasons. We also found higher resilience to environmental changes in generalist species, which is concordant with biotic homogenisation in disturbed communities. However, among the declining species there were also many generalists, which indicates a potential general reduction in this group that goes beyond faunal homogenisation. Given butterflies are biodiversity indicators, these patterns are a possible reflection of an overall impoverishment in biodiversity. © 2016 Elsevier Ltd

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El deute d’extinció: una amenaça latent en una Catalunya canviant?.

Pino J, Guardiola M, Rodà F, Stefanescu C (2011) El deute d’extinció: una amenaça latent en una Catalunya canviant?. L'Atzavara 20: 17-27.

Habitat fragmentation causes immediate and time-delayed biodiversity loss at different trophic levels

Krauss J., Bommarco R., Guardiola M., Heikkinen R.K., Helm A., Kuussaari M., Lindborg R., Öckinger E., Pärtel M., Pino J., Pöyry J., Raatikainen K.M., Sang A., Stefanescu C., Teder T., Zobel M., Steffan-Dewenter I. (2010) Habitat fragmentation causes immediate and time-delayed biodiversity loss at different trophic levels. Ecology Letters. 13: 597-605.
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Doi: 10.1111/j.1461-0248.2010.01457.x

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Intensification or abandonment of agricultural land use has led to a severe decline of semi-natural habitats across Europe. This can cause immediate loss of species but also time-delayed extinctions, known as the extinction debt. In a pan-European study of 147 fragmented grassland remnants, we found differences in the extinction debt of species from different trophic levels. Present-day species richness of long-lived vascular plant specialists was better explained by past than current landscape patterns, indicating an extinction debt. In contrast, short-lived butterfly specialists showed no evidence for an extinction debt at a time scale of c. 40 years. Our results indicate that management strategies maintaining the status quo of fragmented habitats are insufficient, as time-delayed extinctions and associated co-extinctions will lead to further biodiversity loss in the future. © 2010 Blackwell Publishing Ltd/CNRS.

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Extinction debt: a challenge for biodiversity conservation

Kuussaari M., Bommarco R., Heikkinen R.K., Helm A., Krauss J., Lindborg R., Öckinger E., Pärtel M., Pino J., Rodà F., Stefanescu C., Teder T., Zobel M., Steffan-Dewenter I. (2009) Extinction debt: a challenge for biodiversity conservation. Trends in Ecology and Evolution. 24: 564-571.
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Doi: 10.1016/j.tree.2009.04.011

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Local extinction of species can occur with a substantial delay following habitat loss or degradation. Accumulating evidence suggests that such extinction debts pose a significant but often unrecognized challenge for biodiversity conservation across a wide range of taxa and ecosystems. Species with long generation times and populations near their extinction threshold are most likely to have an extinction debt. However, as long as a species that is predicted to become extinct still persists, there is time for conservation measures such as habitat restoration and landscape management. Standardized long-term monitoring, more high-quality empirical studies on different taxa and ecosystems and further development of analytical methods will help to better quantify extinction debt and protect biodiversity. © 2009 Elsevier Ltd. All rights reserved.

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