Abstract. Considerable losses and degradation of heathlands (in moorlands and lowlands) have been reported across Europe, with Calluna vulgaris (heather) being replaced by other species, often grasses. Increasing atmospheric nitrogen deposition and overgrazing have been suggested as the driving factors behind this change. This possibility was investigated in a study of the interacting effects of nutrient inputs and grazing on heather and three grass species (Nardus stricta, Deschampsia cespitosa and D. flexuosa) in the field, on a moorland in northeastern Scotland. In addition, the interacting effects of increasing nutrients and Calluna canopy height on N. stricta and D. cespitosa were studied using turves in an outdoor experimental area. In the field, fencing had a larger effect than fertilizer on the growth of all species, except for N. stricta, the species most unpalatable to herbivores. Fencing led to an increase in the height of the Calluna canopy, which may reduce light availability for the grasses. In the turf experiment, the height of the Calluna canopy affected the diameter of the grass tussocks and percentage of green matter (i.e. live leaf material), with plants under the more closed Calluna canopies being smaller. This study suggests that the slow‐growing, evergreen Calluna is a more effective competitor than the faster growing grasses when it has a tall, intact canopy, even at increased levels of nutrient supply. However, overgrazing promotes gap formation in the Calluna canopy, providing an opportunity for grasses to take advantage of increased nutrients. Thus the conservation of heather moorlands requires an understanding of the grazing level which allows Calluna to maintain sufficient canopy structure to outcompete grasses for light.

Summary1. Spatial variation and covariation in host-plant quality, herbivore abundance and herbivore mortality were examined across the natural geographical range in Europe of holly Ilex aquifolium and the host-specific holly leaf-miner Phytomyza ilicis. 2. Although measures of host-plant quality showed substantial between-site variation, no simple spatial pattern in any of the measures (only phosphorus content and leaf mass showed correlations with latitude, longitude or altitude) was detected, and few correlations with tree or local site characteristics. 3. In contrast, measures of the abundance of the leaf-miner exhibited marked spatial patterns, resulting in a lack of simple covariance between leaf-miner abundance and host-plant quality. 4. Different apparent mortalities of the leaf-miner exhibited varied spatial patterns in their intensity, but no evidence of range-wide density dependence, again resulting in few patterns of covariance between intensity of mortality and measures of host-plant quality. 5. The population dynamics of the holly leaf-miner across its geographical range are complex. At any site, the mortality that a population experiences is the sum of largely independent yet spatially structured components, against a background of varying hostplant quality. Despite lacking any marked spatial structure, host-plant quality may have important local effects. These are difficult to detect regionally, and thus may principally contribute noise to regional patterns of levels of oviposition, abundance and mortality.

No abstract

In the UK, Panolis flammea (Denis & Schiffermüller) is a pest of monocultures of non-native lodgepole pine Pinus contorta Douglas, but not of the indigenous host Scots pine P. sylvestrisL. This difference in population dynamics may be due to the adaptation of P. flammea populations to the phenology, chemical composition and natural enemy complement of lodgepole pine. To ascertain if there was local adaptation of P. flammea populations to lodgepole pine, this study tested for improved performance of both larvae and adults on the host plant species from which they were sourced, compared with their performance on the alternative host plant species. No difference was found in the relative mean performance of populations sourced from Scots pine or lodgepole pine plantations, when fed on Scots or lodgepole pine foliage. Larvae grew faster on Scots pine but this difference did not translate into differences in pupal weight, female body weight or fecundity. Indeed, those insects that had fed on lodgepole pine had a longer lifespan than those that had fed on Scots pine, which, if translated into greater probability of mating or higher fecundity, could contribute to the observed outbreak dynamics in the field. The prediction that the observed outbreak dynamics of P. flammea can be explained by the existence of populations locally adapted to lodgepole pine was not supported. These results cast doubt on the use of larval growth parameters as surrogates of fitness in Lepidoptera.