@article {15270,
	title = {Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks},
	journal = {Oecologia (Berlin)},
	volume = {161},
	number = {3},
	year = {2009},
	month = {September},
	pages = {559-568},
	abstract = {The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0\%) as in Q. ilex (20.0\%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60\%) than in Q. ilex (21\%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects.},
	isbn = {0029-8549},
	author = {Espelta, Josep Maria and Cortes, P. and Molowny-Horas, R. and Retana, J.}
}
@article {14594,
	title = {Acorn crop size and pre-dispersal predation determine inter-specific differences in the recruitment of co-occurring oaks},
	journal = {Oecologia (Berlin)},
	volume = {161},
	number = {3},
	year = {2009},
	month = {September},
	pages = {559-568},
	abstract = {The contribution of pre-dispersal seed predation to inter-specific differences in recruitment remains elusive. In species with no resistance mechanisms, differences in pre-dispersal predation may arise from differences in seed abundance (plant satiation) or in the ability of seeds to survive insect infestation (seed satiation). This study aimed to analyse the impact of pre-dispersal acorn predation by weevils in two co-occurring Mediterranean oaks (Quercus ilex and Quercus humilis) and to compare its relevance with other processes involved in recruitment. We monitored the patterns of acorn production and acorn infestation by weevils and we conducted experimental tests of acorn germination after weevil infestation, post-dispersal predation and seedling establishment in mixed forests. Monitoring and experimental data were integrated in a simulation model to test for the effects of pre-dispersal predation in recruitment. In both oaks pre-dispersal acorn infestation decreased with increasing acorn crop size (plant satiation). This benefited Q. ilex which exhibited stronger masting behaviour than Q. humilis, with almost a single and outstanding reproductive event in 6 years. Acorn infestation was more than twice as high in Q. humilis (47.0\%) as in Q. ilex (20.0\%) irrespective of the number of seeds produced by each species. Although germination of infested acorns (seed satiation) was higher in Q. humilis (60\%) than in Q. ilex (21\%), this could barely mitigate the higher infestation rate in the former species, to reduce seed loss. Conversely to pre-dispersal predation, no inter-specific differences were observed either in post-dispersal predation or seedling establishment. Our results indicate that pre-dispersal predation may contribute to differences in seed supply, and ultimately in recruitment, between co-existing oaks. Moreover, they suggest that seed satiation can barely offset differences in seed infestation rates. This serves as a warning against overemphasising seed satiation as a mechanism to overcome seed predation by insects.},
	isbn = {0029-8549},
	author = {Espelta, Josep Maria and Cortes, P. and Molowny-Horas, R. and Retana, J.}
}
@article {13494,
	title = {Additive effects of aboveground and belowground herbivores on the dominance of spotted knapweed (Centaurea stoebe)},
	journal = {Oecologia (Berlin)},
	volume = {164},
	number = {3},
	year = {2010},
	month = {Nov},
	pages = {701-712},
	abstract = {Spotted knapweed (Centaurea stoebe) is found in over 3 million ha of rangeland and forests across North America, and evidence supporting the use of biological control as a regional method to reduce infestations and their associated impacts remains inconclusive. Several species of insects have been reported to reduce plant densities in some areas; however, rigorous studies that test combinations of these species and the influence of resource availability are lacking. We examined the singular and combined effects of herbivory by a root weevil (Cyphocleonus achates) and a flower head weevil (Larinus minutus) on the growth and flower production of C. stoebe. We also manipulated soil resource fertility as an additional factor that could explain the outcomes of contradictory biological control herbivore effects on C. stoebe. In a greenhouse study, herbivory by C. achates decreased flower production for plants across all resource environments. In a caged common garden study, the negative effects of herbivory also did not interact with soil nutrient status. However, the presence of plant competition further decreased knapweed growth, and the negative effects of concurrent herbivory by C. achates and L. minutus on plant biomass and flower production were additive. Derived within the context of variable levels of soil nutrient availability and competing vegetation, these results support the cumulative stress hypothesis and the contention that combined above- and belowground herbivory can reduce spotted knapweed densities and reduce the ecological and economic impacts of this species in rangelands of western North America.},
	keywords = {Cyphocleonus achates, Larinus minutus},
	isbn = {0029-8549},
	author = {Knochel, David G. and Monson, Nathan D. and Seastedt, Timothy R.}
}
@article {13106,
	title = {Elevated CO2 and aboveground-belowground herbivory by the clover root weevil},
	journal = {Oecologia (Berlin)},
	volume = {162},
	number = {1},
	year = {2010},
	month = {January},
	pages = {209-216},
	abstract = {Predicted increases in atmospheric carbon dioxide (CO2) concentrations are expected to increase primary productivity in many terrestrial ecosystems, which could lead to plants becoming N limited. Studies suggest that legumes may partially overcome this by increasing biological nitrogen fixation. However, these studies have not yet considered how these changes may be affected by the altered dynamics of insect herbivores feeding on the plant. This study investigated how elevated CO2 (700 [mu]l l-1) affected the clover root weevil (Sitona lepidus), a significant pest of white clover (Trifolium repens). Adults feed on leaves aboveground where they lay eggs; soil-dwelling larvae initially feed on root nodules that house N2-fixing bacteria. Foliar C:N ratios rose by 9\% at elevated CO2, but the biggest responses were observed belowground, with increases in root mass (85\% greater) and nodule abundance (220\% more abundant). Root C:N ratios increased significantly from 10.95 to 11.60 under elevated CO2, which increased even further to 13.13 when nodules were attacked by larval S. lepidus. Adult S. lepidus consumed significantly more leaf tissue at elevated CO2 (0.47 cm2 day-1) compared with ambient CO2 (0.35 cm2 day-1), suggesting compensatory feeding, but laid 23\% fewer eggs at elevated CO2. Even though fewer eggs were laid at elevated CO2, 38\% more larvae were recovered suggesting that larval survival was much better under elevated CO2. Increased larval abundance and performance at elevated CO2 were positively correlated with the number of nodules available. In conclusion, reduced foliar quality at elevated CO2 was generally disadvantageous for adult S. lepidus living aboveground, but extremely beneficial for S. lepidus larvae living belowground, due to the enhanced nodulation. Climate change may, therefore, enhance biological nitrogen fixation by T. repens, but potential benefits (e.g. provision of N without chemical fertilizers) may be undermined by larger populations of S. lepidus larvae belowground.},
	keywords = {Sitona lepidus},
	isbn = {0029-8549},
	author = {Johnson, Scott N. and McNicol, James W.}
}
@article {11271,
	title = {Responses of parasitoids to saproxylic hosts and habitat: a multi-scale study using experimental logs},
	journal = {Oecologia (Berlin)},
	volume = {155},
	number = {1},
	year = {2008},
	month = {February},
	pages = {63-74},
	type = {Article},
	abstract = {Species belonging to higher trophic levels are particularly vulnerable to habitat loss and consequential host population declines, but detection of effects depends on observation scale. We investigated the effects of habitat and host availability at multiple scales on parasitoids of early successional saproxylic beetles in middle boreal Sweden, where forestry has led to habitat fragmentation and coarse woody debris (CWD) loss. Parasitoid wasps and beetle hosts were collected from nine locations, each containing three spruce-dominated stand types (clear-cut, mature managed and unmanaged stands), using emergence traps on experimental CWD. We measured local CWD volumes and determined the availability of forests of a suitable age within the landscape. We tested parasitoid responses to stand type, CWD volume, abundance of known and probable hosts and longitude. Additionally, we tested whether parasitoids responded to the area of habitat of a suitable age within radii from 0.2 to 10 km. Stand type appeared in best-fit models for all common species, suggesting that wasps respond strongly to habitat at local scales. Longitude (largely climate) featured commonly, but CWD volume was never significant. Host abundance appeared in best-fit models for three of five common species, proving significant only for Bracon obscurator, the abundance of which correlated with that of Orthotomicus laricis at both trap and site levels. Rhimphoctona spp. also correlated significantly with its known host Tetropium castaneum at the trap level. B. obscurator responded to habitat area at scales of 0.6-1 km and Cosmophorus regius responded at radii greater than 7 km, while the larger species did not respond strongly to habitat area. The role of habitat area at greater scales thus varied greatly amongst species, but our data suggest that dispersal of these common early successional species may not be strongly restricted at the current scale of fragmentation of their boreal habitats.},
	keywords = {Dryocoetes, Hylastes, Hylurgops, Ips typographus, Orthotomicus, Pityogenes},
	isbn = {0029-8549},
	author = {Gibb, H. and Hilszczanski, J. and Hjalten, J. and Danell, K. and Ball, J. P. and Pettersson, R. B. and Alinvi, O.}
}
@article {9437,
	title = {Multi-trophic effects of ungulate intraguild predation on acorn weevils},
	journal = {Oecologia (Berlin)},
	volume = {152},
	number = {3},
	year = {2007},
	month = {June},
	pages = {533-540},
	abstract = {Predators and parasitoids may contribute to controlling the population sizes of phytophagous insects, and this has been shown to benefit plants. Phytophagous insects may also be killed by other herbivores (intraguild predation), usually larger-sized vertebrates that ingest insects accidentally while feeding on common food sources. We studied the intraguild predation on acorn weevils by ungulates and assessed the consequences for weevil populations. Infested acorns are prematurely abscised and the weevil larvae finish their development inside the acorns after being dropped. Our results show that weevil larvae were killed by ungulates eating the infested acorns on the ground. Ungulates did not discriminate between infested and sound acorns, and the probability of a larva being incidentally eaten was inversely related to acorn availability. Thus, predation risk was enhanced by the premature drop of infested acorns when acorn availability on the ground was low. Predation rates on infested acorns were much higher where ungulates were present, and acorn infestation rates were significantly lower. However, ungulates did not provide the oaks any net benefit, since the reduction of infestation rates was not enough to compensate for the large amounts of sound acorns eaten by ungulates. Seed predation is usually studied as a progressive loss of seeds by pre- and post-dispersal predators, but the interactions between them are usually not considered. We show that intraguild predation on insects by large ungulates had an effect on the structure of the foraging guild, as the proportion of acorns predated by insects decreased; however, replicating the same experimental design in different ecological scenarios would increase the strength of these results. In conclusion, the present study shows the importance of considering the multi-trophic interactions between seed predators in order to have a complete picture of granivory.},
	keywords = {Curculio},
	isbn = {0029-8549},
	author = {Bonal, Raul and Munoz, Alberto}
}
@article {9435,
	title = {Complex selection on life-history traits and the maintenance of variation in exaggerated rostrum length in acorn weevils},
	journal = {Oecologia (Berlin)},
	volume = {167},
	number = {4},
	year = {2011},
	month = {Dec},
	pages = {1053-1061},
	abstract = {Trophic interactions can trigger the development of exaggerated specialized characters and promote morphological diversification. For example, acorn weevils (genus Curculio) present strikingly long rostrums, which are used by females to perforate oviposition holes through the seed coat. Species exhibiting longer rostrums are known to exploit larger acorns, and therefore rostrum length is thought to be subject to selection to match the preferred acorn type. However, rostrum length is strongly correlated with body size, and morphological divergence could result from either selection on rostrum length for optimal food exploitation or from other pressures acting on body size. We collected infested acorns at oak forests where the large Curculio elephas and the small-bodied Curculio glandium co-occur. There were no interspecific differences in adult female body size to rostrum length allometric relationships, and rostrum length is equally correlated with body size in either species. MtDNA-based species identification showed that C. glandium larvae were present within acorns of all sizes, whereas C. elephas larvae were restricted to acorns above a minimum size, irrespective of oak species. Hence, exploitation of large acorns can hardly have triggered rostrum enlargement, as the small sized C. glandium adults (with short rostrums) could perforate and oviposit in both small and large acorns. Rather, increased rostrum length is probably a by-product of the larger body sizes of individuals emerging from bigger acorns, which allow increased larval size and enhance larval survival likelihood. Summarizing, when exaggerated feeding traits co-vary with other body features, interspecific morphological variability may result from contrasting selective pressures acting on these correlated characters.},
	keywords = {Curculio, Curculio elephas},
	isbn = {0029-8549},
	author = {Bonal, Raul and Espelta, Josep Maria and Vogler, Alfried P.}
}
@article {6000,
	title = {Host resistance elicited by methyl jasmonate reduces emission of aggregation pheromones by the spruce bark beetle, Ips typographus},
	journal = {Oecologia (Berlin)},
	volume = {167},
	number = {3},
	year = {2011},
	month = {Nov},
	pages = {691-699},
	abstract = {We treated Norway spruce (Picea abies) stems with methyl jasmonate (MeJA) to determine possible quantitative and qualitative effects of induced tree defenses on pheromone emission by the spruce bark beetle Ips typographus. We measured the amounts of 2-methyl-3-buten-2-ol and (S)-cis-verbenol, the two main components of the beetle{\textquoteright}s aggregation pheromone, released from beetle entrance holes, along with phloem terpene content and beetle performance in MeJA-treated and untreated Norway spruce logs. As expected, phloem terpene levels were higher and beetle tunnel length was shorter (an indication of poor performance) in MeJA-treated logs relative to untreated logs. Parallel to the higher phloem terpene content and poorer beetle performance, beetles in MeJA-treated logs released significantly less 2-methyl-3-buten-2-ol and (S)-cis-verbenol, and the ratio between the two pheromone components was significantly altered. These results suggest that host resistance elicited by MeJA application reduces pheromone emission by I. typographus and alters the critical ratio between the two main pheromone components needed to elicit aggregation. The results also provide a mechanistic explanation for the reduced performance and attractivity observed in earlier studies when bark beetles colonize trees with elicited host defenses, and extend our understanding of the ecological functions of conifer resistance against bark beetles.},
	keywords = {Ips typographus},
	isbn = {0029-8549},
	author = {Zhao, Tao and Borg-Karlson, Anna-Karin and Erbilgin, Nadir and Krokene, Paal}
}
