Carregant...
Tipus de document
TesiVersió
Versió publicadaData de publicació
Llicència de publicació
Si us plau utilitzeu sempre aquest identificador per citar o enllaçar aquest document: https://hdl.handle.net/2445/128064
Pre-dispersal seed predation by weevils (Curculio spp.): The role of host-specificity, resource availability and environmental factors
Títol de la revista
Autors
Director/Tutor
ISSN de la revista
Títol del volum
Recurs relacionat
Resum
[eng] Pre-dispersal seed predation (PDSP, hereafter) significantly reduces plant reproductive output. The negative effects on plant fitness have triggered the development of different strategies to protect the seeds and/or reduce the impact of PDSP. These strategies, in turn, have promoted insect trophic specialization by means of morphological, physiological and behavioral adaptations. The close relationship between specialist insects and their host plants conditions insect community assemblage and population dynamics. Specialization would favour multi-species co-occurrence according to the Competitive Exclusion Principle, as different species cannot use the same limited resources. At the same time, specificity makes these species strongly dependent on a particular trophic resource, so that host plant population dynamics may lead to bottom-up forces influencing insect numbers. In this Thesis, I have studied the consequences of trophic specialization on species assemblage and demography in the most prevalent pre-dispersal predators of oak Quercus spp., chestnuts Castanea sativa and hazelnut Corylus avellana seeds, namely the weevils of the genus Curculio (Coleoptera: Curculionidae). Using DNA barcoding I could identify larvae infesting the seeds to the species level and hence assess resource partitioning among Curculio spp. in oak-hazelnut mixed forests. These forests were distributed along a latitudinal gradient in which the degree of overlap in the timing of seeding between the two species differed. The results showed that there was a strict host-based segregation, as the species found in hazelnuts was never recorded on oak acorns and vice versa. Contrary to other studies, segregation of seed parasites was not driven by seed size, as the seeds of both plants were large enough to host the larvae of any species. Rather, co-existence was more likely modulated by the combination of time partitioning, and probably by dissimilarities in dispersal-dormancy strategies among weevils. The timing of oogenesis differs among Curculio spp. and does the timing of seeding between oaks and hazelnuts. Early maturing hazelnuts are thus exploited only by Curculio nucum, as its eggs mature earlier too. Such specialization on a patchily distributed host plant conditioned its population genetics, as gene-flow between populations showed restrictions undetected in the other Curculio spp. that fed on the widespread oaks. Regarding the bottom-up effects of food availability on insect numbers we assessed that, as expected, irregular seed crops (masting) conditions weevil population dynamics and certainly help reducing acorn predation in Mediterranean oaks. However, we found that the effects of rainfall stochasticity on the success of weevil emergence from the soil (i.e. rain is needed to soften the soil) contributed to decrease seed predation in a similar magnitude to masting. The present Thesis stresses the need of introducing the time/phenology component (i. e. egg maturation, timing of seeding) to assess the mechanisms underlying host plant-specialist insect associations. Also, it shows that, despite their specificity, other environmental variables apart from food availability condition weevil numbers. This result must be considered in further studies on the significance of oak masting as a strategy to reduce pre-dispersal seed predation. Lastly, the results provide an insight into the potential consequences of Global Change on the communities of these specialist insects linked to oaks. The populations of a narrow specialist like the hazelnut feeding C. nucum will be very vulnerable to forest fragmentation, which will reduce more severely inter-population gene-flow and lead to population bottlenecks. In turn, climate change (e.g. temperature rising, rainfall decrease) could disrupt the matching phenologies of insects and their host plants and reduce insect population size.
Matèries (anglès)
Citació
Citació
ARIAS-LECLAIRE, Harold. Pre-dispersal seed predation by weevils (Curculio spp.): The role of host-specificity, resource availability and environmental factors. [consulta: 13 de desembre de 2025]. [Disponible a: https://hdl.handle.net/2445/128064]