Pre-dispersal acorn predation in mixed oak forests: interspecific differences are driven by the interplay among seed phenology, seed size and predator size (original) (raw)
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Invasive oaks escape pre-dispersal insect seed predation and trap enemies in their seeds
Integrative zoology, 2018
Species introduced to habitats outside their native range often escape control by their natural enemies. Besides competing with native species, an alien species might also affect the native herbivores by introducing a new source of different quality food. Here, we describe the case of northern red oak (Quercus rubra) invasion in Europe. We collected data on insect (moth Cydia spp. and weevil Curculio spp.) seed predation of northern red oak in its native (USA, North America) and invasive (Poland, Europe) range, as well as for sessile oaks (Quercus petrea) in Europe. We also evaluated the quality of acorns as hosts for weevil larvae by collecting infested acorns and measuring weevil developmental success, and quantifying acorn traits such as seed mass, tannins, lipids and protein concentration. We used DNA barcoding to identify insects to the species level. The predation by moths was similar and very low in both species and in both ranges. However, red oaks escape pre-dispersal seed ...
Satiation of predispersal seed predators: the importance of considering both plant and seed levels
Evolutionary Ecology, 2007
Plants can reduce the fitness costs of granivory by satiating seed predators. The most common satiation mechanism is the production of large crops, which ensures that a proportion of the seeds survive predation. Nevertheless, satiation of small granivores at the seed level may also exist. Larger seeds would satiate more efficiently, enhancing the probability of seed survival after having been attacked. However, a larger seed size could compromise the efficiency of satiation by means of large crops if there were a negative relationship between seed size and the number of seeds produced by an individual plant. We analyze both types of satiation in the interaction between the holm oak Quercus ilex and the chestnut weevil Curculio elephas. Both crop size and acorn size differed strongly in a sample of 32 trees. Larger crop sizes satiated weevils, and higher proportions of the seeds were not attacked as crop size increased. Larger seeds also satiated weevil larvae, as a larger acorn size increased the likelihood of embryo survival. Seedling size was strongly related to acorn size and was reduced by weevil attack, but seedlings coming from large weeviled acorns were still larger. The number and the size of the acorns produced by individual trees were negatively related. Larger proportions of the crop were infested in oaks producing less numerous crops of larger acorns. However, contrary to expectations, these trees did not satiate more effectively at the seed level either. Effective satiation by larger acorns was precluded by larger multi-infestation rates associated to smaller seed crops, in such a way that the proportion of attacked seeds that survived did not vary among trees with different acorn sizes. These results highlight the need of considering satiation by means of large crops and large seeds in studies of predispersal seed predation. Long-term monitoring on individual oaks will help to assess whether there is a trade-off between the number and the size of the acorns Ó Springer Science+Business Media B.V. 2006 and, if it existed, how it could condition the fitness consequences of both types of satiation.
Ecological Entomology, 2007
1. The abscission of seeds infested by insects is common in many plants and has been proposed as a defensive mechanism, although its negative consequences for insects have rarely been assessed. 2. We assessed the consequences of seed abscission studying the interactions between the holm oak Quercus ilex and the chestnut weevil Curculio elephas , its main predispersal seed predator. Female weevils oviposit into the acorns and the larvae must complete their development inside a single acorn feeding on the cotyledons. The growth of the infested acorns is suppressed because they are prematurely abscised. 3. Female weevils oviposit along the acorn growing period; hence, the size of the infested acorns increased with date. The growth of the larvae inside the smaller, early infested, acorns was constrained because food (i.e. cotyledons) was frequently depleted. Larval size increased with the date along with the size of the infested acorns, but it declined slightly in the latest dates as a result of the higher conspecific competition provoked by the larger number of larvae per acorn. 4. The present results demonstrate that premature seed abscission by Q. ilex had negative consequences for C. elephas , as a smaller acorn size reduced food availability and constrained larval size, a key insect life history trait. At the same time, it is suggested that the growth suppression of infested acorns may condition the oviposition phenology of these insects according to their body size. These results need to be considered in further research in the context of the evolutionary significance of premature seed abscission as a defensive mechanism.
2021
Simple Summary Seed predation is an antagonistic interaction that can limit plant population dynamics. We investigated the interaction between Quercus faginea and two specialized pre-dispersal insect seed predators (weevils and moths) during two years of contrasting crop size to determine the consequences of oak reproductive investment on seed production and insect performance. Crop and acorn size were lower during the second year, although seed predation rates by insects were similar during both crop years. Oaks producing more acorns reduced seed predation by insects during the large crop year and thus improved their reproductive success, and those producing bigger acorns experienced higher levels of seed predation, and more insect larvae developed inside the available acorns during the low crop year. Inter- and intra-specific insect competition increased during the low crop year and were affected by tannin content in acorns. Despite substantial between-year variations in crop and ...
Integrative Zoology, 2017
Insect herbivory decreases plant fitness by constraining plant growth, survival and reproductive output. Most studies on the effects of herbivory in trees rely on correlational inter-individual comparisons and could thus be affected by confounding factors linked to both herbivory and plant performance. Using the Mediterranean Holm oak (Quercus ilex) as study model, we followed an experimental approach in which leaf-feeding insects (mainly This article is protected by copyright. All rights reserved. Lepidoptera caterpillars) were excluded from some shoots in all study trees. Shoots subjected to herbivore exclusion exhibited lower defoliation rates and produced more acorns than control shoots. Defoliation constrained shoot growth throughout the study period, but had no effect on the number of female flowers produced per shoot. Acorn production was, however, lower in control shoots due to their higher abortion rates, and also to their greater mortality risk during summer drought, as shoots with fewer leaves were less likely to survive. Plant reaction to herbivory inhibits certain physiological pathways involved in plant growth what, together with the effects of physical damage, reduce the amount and efficiency of the photosynthetic tissue. This increases their vulnerability to environmental stresses such as water deficit, which limit resource assimilation. Defoliation should occupy a main place among the factors affecting oak regeneration, as it may suppose a significant source of seed loss previous to pre-dispersal acorn predation. Further experimental studies could help to elucidate its effects in contrasting environments. In Mediterranean regions, the harsher droughts predicted by Climate Change models could worsen the effects of insect herbivory on oak reproductive output.
Intraguild predation of weevils by livestock reduces acorn pests in oak silvopastoral systems
Journal of Pest Science, 2020
Iberian oak savannahs are traditional silvopastoral systems in which acorns constitute a key food source for livestock. Acorn feeding insects provoke significant economic losses; however, the high natural value of Iberian oak savannahs precludes any chemical treatment. This paper shows a novel way of biological pest control based on promoting livestock predation on these insects. Female Curculio elephas (Coleoptera: Curculionidae) oviposit into developing acorns, which are prematurely abscised before reaching their potential size. Larvae still spend 20 days feeding on the cotyledons after acorn drop, being during this period very vulnerable to predation by livestock. We experimentally assessed that cows, pigs and sheep ate sound and infested acorns in the same proportion, so that infestation rates were lower in those Iberian oak savannahs in which livestock density was higher. An effective biological control of Curculio elephas weevils should involve an early predation of infested acorns by livestock, preferentially within 10 days after falling. Doing this, most larvae will be predated before completing their development and, in addition, the nutritional value of infested acorns will still be high (cotyledons not yet depleted by weevils). We encourage landowners to increase livestock densities during September-October, when the infested acorn dropping peaks. These increased densities should rotate over the farm and be maintained at the same plot for a maximum of 3 years in a row. Otherwise, a prolonged and concentrated livestock predation on sound acorns and seedlings would hamper long-term oak regeneration. Keywords Natural pest control • Dehesa • Curculio elephas • Livestock management • Ecological intensification • Intraguild predation Key messages • Curculio elephas provokes large acorn losses in Iberian oak savannahs with free-range livestock. • Infested acorns are prematurely abscised, thus making larvae vulnerable to predation by large post-dispersal seed predators. • Livestock consumes early dropped infested acorns in the same proportion than sound ones. • High livestock densities when infested acorn dropping peaks (September-October) reduce acorn infestation rates. • Locally increased livestock density can control acorn pests, but it should rotate among areas within the farms to avoid long-term harmful effects on oak regeneration. Communicated by C. Stauffer.
Positive cascade effects of forest fragmentation on acorn weevils mediated by seed size enlargement
Insect Conservation and Diversity, 2012
1. Today, forest fragmentation is one of the major threats to biodiversity worldwide. In this context, fragmented populations of specialised forest organisms face an increasing risk of extinction because of factors such as local food scarcity. Nonetheless, the role of food availability may differ depending on organism size, which is expected to determine the energy requirements and mobility between fragments.