Acorn - weevil interactions in a mixed-oak forest: Outcomes for larval growth and plant recruitment

Munoz A., Bonal R., Espelta J.M. (2014) Acorn - weevil interactions in a mixed-oak forest: Outcomes for larval growth and plant recruitment. Forest Ecology and Management. 322: 98-105.
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Doi: 10.1016/j.foreco.2014.02.039

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Weevils are the most important pre-dispersal acorn predators in the Mediterranean region, where oaks often form mixed forests and different weevil species can coexist. The performance of weevil larvae depends in great extent on their feeding activities inside the infested acorns that, in turn, are known to reduce the viability of acorns. In this paper, we have analysed the interactions among the weevil community and four oak species (Quercus pyrenaica, Quercus suber, Quercus faginea and Quercus ilex) coexisting in a Mediterranean mixed-oak forest. DNA sequencing of weevil larvae revealed four different weevil species (Curculio elephas, Curculio glandium, Curculio pellitus and Curculio venosus) infesting the acorns of the four oak species. Oak species differed in acorn size, and weevil species also differed in body size. Weevil species showed some degree of specificity among the four oak species, but specificity was not related to variations in acorn size. By contrast, larval development and seedling recruitment were mostly driven by inter-specific differences in larval and acorn size. Larger seeded species suffered less seed damages by weevils (i.e. embryo predation and cotyledon consumption), thus reducing the impacts of acorn infestation in seedling emergence and seedling size. Larval development for the largest weevil species C. elephas was constrained by cotyledon depletion in all acorn species. Yet, this pattern was not observed for other weevil species. Larval size of the same weevil species also varied among different oak species after controlling for the amount of cotyledon eaten by larvae, thus, variation of other acorn traits among acorn species (e.g. chemical composition) may also have consequences for the performance of weevil larvae. It is likely that other variables operating at population level, such as temporal and spatial changes in acorn production or phenological variations of weevils and oaks, are also implicated in the complex functioning of these outstanding mixed-oak forests where natural regeneration seems to be threatened. © 2014 Elsevier B.V.

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Variation of predator satiation and seed abortion as seed defense mechanisms across an altitudinal range

Peguero G., Bonal R., Espelta J.M. (2014) Variation of predator satiation and seed abortion as seed defense mechanisms across an altitudinal range. Basic and Applied Ecology. 15: 269-276.
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Doi: 10.1016/j.baae.2014.03.006

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Predator satiation and seed abortion have been reported as effective mechanisms reducing pre-dispersal seed predation, however, whether they may act simultaneously and whether their contribution to seed defense may spatially vary has been barely addressed. Across the altitudinal range of the dry tropical tree Acacia pennatula we investigated the importance of seed production and seed abortion as defense mechanisms against its pre-dispersal seed predators (Mimosestes spp.). Additionally, we measured the potential relationship between the number of seeds that escaped predation and plant recruitment. Predator satiation was effective since greater fruit production was associated with a lower proportion of predated seeds, while high seed abortion rates were related to increases in larval mortality. Although both mechanisms were present simultaneously, their relative contribution varied considerably across the altitudinal range: predator satiation was favored in the middle parts of the range, where seed production is much higher, whereas seed abortion was particularly relevant at the peripheral sites and especially high at the upper margin. The number of seeds that escaped predation was related to seedling density at plot level, indicating the demographic significance of these defense mechanisms against pre-dispersal seed predation. Overall, these results highlight the importance of considering spatial variability when analyzing seed defense traits and they also suggest considering predator satiation and seed abortion as two complementary mechanisms to reduce seed loss. © 2014 Gesellschaft für Ökologie.

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Endozoochory and Fire as Germination Triggers in Neotropical Dry Forests: An Experimental Test

Peguero G., Espelta J.M. (2014) Endozoochory and Fire as Germination Triggers in Neotropical Dry Forests: An Experimental Test. Biotropica. 46: 83-89.
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Doi: 10.1111/btp.12076

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Endozoochory and fire are crucial ecological factors determining germination success and recruitment in many plant species. Fire is a well-known germination trigger while endozoochory may allow seed dispersal along with an increase in germination. Their interaction has rarely been addressed, however, even though both factors are pervasive in human-transformed ecosystems like most Neotropical Dry Forests (NDF). For three common Mesoamerican tree species (Acacia pennatula, Enterolobium cyclocarpum, and Guazuma ulmifolia), we used feeding trials to assess the preference of cattle, which are their main seed dispersal agent. We also experimentally tested the interaction between gut passage and fire as triggers of germination. The fruits of the three species were eaten by cattle, but the small seeds of G. ulmifolia were ingested 10-fold more than those of the other species. While gut passage did not have any effect on germination, heat-shocks above 90 °C increased the number of germinating seeds by 15 percent. These results suggest that cattle may be a key dispersal vector in NDF, but that fire may be an important germination trigger. Physical dormancy in these species may have been selected for by extinct megaherbivores because it was a key trait ensuring seed survival after gut passage. However, in light of the recent expansion of cattle-ranching and fire occurrence in NDF, it has become a useful exaptation facilitating the colonization of disturbed areas. © 2013 The Association for Tropical Biology and Conservation.

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Land use change trajectories, conservation status and social importance of dry forests in Nicaragua

Ravera F., Tarrason D., Espelta J.M. (2014) Land use change trajectories, conservation status and social importance of dry forests in Nicaragua. Environmental Conservation. : 0-0.
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Doi: 10.1017/S0376892914000186

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Interdisciplinary studies have proved the interconnectedness of history and ecology relevant to forest conservation proposals and management policies. Engaging local views and concerns in the evaluation and monitoring process can lead to more robust knowledge in the pursuit of effective conservation. This study aimed to assess the degree to which land use change trajectories influence the state of tropical dry forest conservation, as evaluated by scientists and local people. Focusing on northern Nicaragua, the research identified three historical trajectories for types and magnitude of forest disturbance. The assessment process included inventorying sites under different trajectories and integrating ecological and social indicators (namely local perceptions of biodiversity value and concern over species threat). The different land use change trajectories had no influence on the present structure of the dry forest, but strongly affected species diversity, composition and their social importance. The study provided evidence of positive species selection by farmers, which suggested a feedback loop between ecological conditions, social value and awareness of conservation. Copyright © Foundation for Environmental Conservation 2014.

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Seeding phenology influences wood mouse seed choices: The overlooked role of timing in the foraging decisions by seed-dispersing rodents

Sunyer P., Espelta J.M., Bonal R., Munoz A. (2014) Seeding phenology influences wood mouse seed choices: The overlooked role of timing in the foraging decisions by seed-dispersing rodents. Behavioral Ecology and Sociobiology. 68: 1205-1213.
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Doi: 10.1007/s00265-014-1731-x

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Scatter-hoarding rodents influence the population dynamics of plants by acting as seed predators and dispersers. Therefore, rodent foraging preferences for certain seed traits (species, size, condition) have been extensively studied. However, to what extent these preferences are fixed or they track the temporal changes on seed characteristics due to phenological differences has been seldom explored. We studied the temporal variability in seed preferences by wood mouse (Apodemus sylvaticus), according to phenological changes in seed characteristics of two co-occurring oaks (Quercus ilex and Quercus pubescens). The phenology of acorn abundance and the acorn predation/dispersal patterns by rodents were monitored over an entire seeding season. Results revealed temporal changes in rodent preferences for acorns of the two oaks, matching their different seeding phenology (earlier in Q. pubescens and later in Q. ilex). On the other hand, whatever the species considered, rodents preferred larger and sound acorns along the entire season, although the dispersal of infested ones increased slightly during the peaks of acorn drop. The observed influence of seeding phenology on seed choices by rodents warns about inferring definite conclusions regarding their foraging behavior when arising from short-term experiments. Indeed, this study reveals that foraging preferences may be highly dynamic and context-dependent for some seed traits (e.g., species and condition), rather than fixed behavioral patterns. Plasticity in rodent foraging choices may allow them to successfully exploit different oaks with uncoupled seeding phenologies, while potentially favoring their coexistence. © 2014 Springer-Verlag Berlin Heidelberg.

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