The effects of climate change on oaks Quercus spp. Therefore, although isolated trees in the urban matrix harbor smaller populations of pre-dispersal seed predators than forest trees, their interactions with the two main groups of insects feeding on acorns are maintained, which points to their importance for the conservation of urban biodiversity. castanea seed size did not affect predation by moth larvae.
A positive relationship between seed predation by weevils and seed size was found in Q. Seed predation decreased similarly for weevils and moths in isolated trees, so we failed to find support for our second hypothesis. Inversely, predation by moths was higher in Q. rugosa, 0.93), than in the species with small acorns (Q. When only predated acorns were analyzed, predation by weevil larvae was larger than predation by moths in both oak species, although the probability of predation by weevils was higher in the oak species having large acorns (Q. The probability of predation was larger in acorns from trees in the forest (0.30) than in those from isolated trees (0.07), which confirmed the first hypothesis tree species identity did not have a significant effect on the proportion of predated acorns. From the whole sample, 17.3% of the acorns were predated by weevils and 3.8% by moths. We collected 1200 acorns of the two oak species (ten trees per species) in a protected oak forest and a nearby highway in southern Mexico City. Finally, we expected that moth predation would increase with seed size, as it does in weevils. A second hypothesis, based on reports that moths exhibit larger dispersal distances than weevils, was that isolated trees would have higher predation levels from moths than from weevils compared to their respective proportions in forest trees. Our hypothesis was that, since pre-dispersal seed predation depends on insect dispersal, acorns from isolated trees would have lower predation levels than acorns from trees in the forest. We compared these interactions between trees located in a protected forested area and trees isolated in an urban matrix. In this work we analyzed pre-dispersal seed predation by the two main groups of insects, weevils (Coleoptera Curculionidae) and moths (Lepidoptera: Tortricidae), whose larvae feed on the acorns of two oak species (Quercus rugosa and Q. However, it is still unknown the extent to which isolated trees, immersed in an urban matrix, maintain their interactions with insects that feed on their seeds. The implications of these findings to the development of sampling schemes for ecological studies of acorn and acorn-boring insects are also discussed.Īs urbanization proceeds, natural ecosystems surrounding cities are transformed, but usually some elements persist, notably trees from forest ecosystems. Possible mechanisms for explaining the dissimilar distribution of total and infested acorns within crown strata are discussed. Of those acorns found to contain insect larvae, 66% contained C. Dissection of 501 acorns revealed infestation rates of 38%. Significantly more infested acorns occurred in sampling strata within the northeasterly and south-facing sections of the crown. Within crowns, most acorns occurred in sampling strata within the south-facing section. Peak numbers of infested acorns appeared in mid-September. The frequency of insect-infested acorns on shoots during the season resembled a random distribution however, this resemblance was not significant. Acorn numbers were most abundant in May and logarithmically declined throughout the season. Overall, 25% of all acorns examined on shoots of sample trees revealed signs of insect-boring activity. Nine sampling strata in the tree crown were vertically aligned into blocks of three, each facing a different compass direction (NE, S, and NW). Terminal shoots from coast live oaks, Quercus agrifolia Neé, were sampled to determine the abundance and spatial distribution of acorns infested by the filbert weevil, Curculio occidentis (Casey), and the filbertworm, Cydia latiferreana (Walsingham), at a site in northern California during 1989.
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