viernes, 29 de mayo de 2020

Land-use history impacts functional diversity across multiple trophic groups 

Le Provost et al., 2019

Land-use change is a major driver of biodiversity loss worldwide. Although biodiversity often shows a delayed response to land-use change, previous studies have typically focused on a narrow range of current landscape factors and have largely ignored the role of land-use history in shaping plant and animal communities and their functional characteristics. Here, we used a unique database of 220,000 land-use records to investigate how 20-y of land-use changes have affected functional diversity across multiple trophic groups (primary producers, mutualists, herbivores, invertebrate predators, and vertebrate predators) in 75 grassland fields with a broad range of land-use histories. The effects of land-use history on multitrophic trait diversity were as strong as other drivers known to impact biodiversity, e.g., grassland management and current landscape composition. The diversity of animal mobility and resource-acquisition traits was lower in landscapes where much of the land had been historically converted from grassland to crop. In contrast, functional biodiversity was higher in landscapes containing old permanent grasslands, most likely because they offer a stable and high-quality habitat refuge for species with low mobility and specialized feeding niches. Our study shows that grassland-to-crop conversion has long-lasting impacts on the functional biodiversity of agricultural ecosystems. Accordingly, land-use legacy effects must be considered in conservation programs aiming to protect agricultural biodiversity. In particular, the retention of permanent grassland sanctuaries within intensive landscapes may offset ecological debts.

Importance of the drivers of multitrait diversity, mobility trait diversity, resource-acquisition trait diversity, and body size trait diversity. Relative effects (% R2), resulting from a model averaging procedure, were calculated for each group of predictors (i.e., land-use history, current land use, and the species pool). All predictors were scaled to interpret parameter estimates on a comparable scale. Note that for mobility, resource-acquisition, and body size trait diversity, we focused on animal traits and excluded plant traits from the analyses. Results were consistent considering spatial scales ranging from 500 to 1500 m radii surrounding the sampled grasslands.


miércoles, 27 de mayo de 2020

On a first approximation, and setting aside vertebrate chauvinism, it can be said that essentially all organisms are insects.

Robert May
Third generation of Desert Locusts about to hit East and Central Africa.
Photo: oxfam 

martes, 26 de mayo de 2020

Water lily harvest in Vietnam.
Images: Pham Huy Trung, via @mediasocum on Instagram
Epidemias - Una Perspectiva Ecológica

lunes, 25 de mayo de 2020

domingo, 24 de mayo de 2020

Increasing crop heterogeneity enhances multitrophic diversity across agricultural regions  
Sirami et al., 2020

Agricultural landscape homogenization has detrimental effects on biodiversity and key ecosystem services. Increasing agricultural landscape heterogeneity by increasing seminatural cover can help to mitigate biodiversity loss. However, the amount of seminatural cover is generally low and difficult to increase in many intensively managed agricultural landscapes. We hypothesized that increasing the heterogeneity of the crop mosaic itself (hereafter “crop heterogeneity”) can also have positive effects on biodiversity. In 8 contrasting regions of Europe and North America, we selected 435 landscapes along independent gradients of crop diversity and mean field size. Within each landscape, we selected 3 sampling sites in 1, 2, or 3 crop types. We sampled 7 taxa (plants, bees, butterflies, hoverflies, carabids, spiders, and birds) and calculated a synthetic index of multitrophic diversity at the landscape level. Increasing crop heterogeneity was more beneficial for multitrophic diversity than increasing seminatural cover. For instance, the effect of decreasing mean field size from 5 to 2.8 ha was as strong as the effect of increasing seminatural cover from 0.5 to 11%. Decreasing mean field size benefited multitrophic diversity even in the absence of seminatural vegetation between fields. Increasing the number of crop types sampled had a positive effect on landscape-level multitrophic diversity. However, the effect of increasing crop diversity in the landscape surrounding fields sampled depended on the amount of seminatural cover. Our study provides large-scale, multitrophic, cross-regional evidence that increasing crop heterogeneity can be an effective way to increase biodiversity in agricultural landscapes without taking land out of agricultural production.

(A) Traditional and (B) alternative representations of agricultural landscape heterogeneity, focusing either on seminatural heterogeneity or crop heterogeneity, are associated with distinct hypotheses.

viernes, 22 de mayo de 2020

Believe me who have tried. Thou wilt find something more in woods than in books. Trees and rocks will teach what thou canst not hear from a master.​

Bernard of Clairvaux (1841).

jueves, 21 de mayo de 2020

Self-perpetuating ecological–evolutionary dynamics in an agricultural host–parasite system 
Ives et al. 2020

Ecological and evolutionary processes may become intertwined when they operate on similar time scales. Here we show ecological–evolutionary dynamics between parasitoids and aphids containing heritable symbionts that confer resistance against parasitism. In a large-scale field experiment, we manipulated the aphid’s host plant to create ecological conditions that either favoured or disfavoured the parasitoid. The result was rapid evolutionary divergence of aphid resistance between treatment populations. Consistent with ecological–evolutionary dynamics, the resistant aphid populations then had reduced parasitism and increased population growth rates. We fit a model to quantify costs (reduced intrinsic rates of increase) and benefits of resistance. We also performed genetic assays on 5 years of field samples that showed persistent but highly variable frequencies of aphid clones containing protective symbionts; these patterns were consistent with simulations from the model. Our results show (1) rapid evolution that is intertwined with ecological dynamics and (2) variation in selection that prevents traits from becoming fixed, which together generate self-perpetuating ecological–evolutionary dynamics.

Field experiment showing eco–evo dynamics. Between mid-summer and autumn 2015 (panels on the left), the asynchronous harvesting treatment was applied in two hoop houses to maintain aphid habitat and increased parasitoid populations (top two panels) or synchronously to decrease parasitism pressure on aphids (bottom two panels). We counted aphids (solid and dashed black lines for the two hoop houses in each treatment) by visual inspection of 500 stems per cage; s.e.m. bars are given but in some cases are covered by the dots. Our index of parasitism (red lines) is the number of mummies as a proportion of the number of mummies and aphids. Peak parasitism rates (on 20 and 26 August and 2 September 2015) were higher in the asynchronous hoop houses (P = 0.007, Supplementary Information). The narrow panels give the estimated demographic rates (for the hoop houses in the panels above them) from the fitted model (Extended Data Fig. 8). The estimated daily parasitoid attack rates (a(t) in equation (2)) is given in red and the densityindependent relative aphid survival (z(t) in equation (2)) is given in blue, with solid and dashed lines corresponding to the two replicates. Note that the relative aphid survival is scaled to the maximum estimated survival in 2015, so values greater than 1 in 2016 imply higher survival than the 2015 maximum. The estimated proportion of resistant clones is given by black lines and the black points with s.e.m. give the proportion of Hamiltonella–APSE3 clones from the genetic symbiont surveys.


martes, 19 de mayo de 2020

Young seedling of Arabidopsis thaliana, with red-colored nuclei and green-colored cell membraneses 
Photo: Fernan Federici