No abstract

Butterfly assemblages within lowland monsoon forest were compared at four sites on Sumba, Indonesia that differed in terms of protection and exhibited associated differences in levels of human disturbance. A numerical method employing principal components analysis was devised for describing forest structure at each site. The first principal component (PRINI) grouped attributes tending towards dense forest with closely-spaced trees, a closed canopy and a poorly developed field layer, with trees that tended to be large with the point of inversion in the upper half of the trunk. The highest values for PRINI were recorded within protected forest, and PRINl values were considered to be a useful index of forest disturbance at each site. Species diversity of butterflies was highest in unprotected secondary forest. but was not affected by lower levels of disturbance. Those species occurring at highest density in secondary forest generally had wide geographical distributions, whereas those species occurring at highest density in undisturbed primary forest had restricted ranges of distribution, in most cases with a separate subspecies on Sumba. Overall, an index of biogeographical distinctiveness decreased with increasing disturbance, and this supports the hypothesis that the most characteristic species of undisturbed climax forest have the smallest geographical ranges of distribution. Species abundance data for butterflies fitted a log-normal distribution at all but the most disturbed site. These results indicate that the pattern of proportional abundance of tropical butterfly species may be used as an 'instantaneous' indicator of forest disturbance, and that changes in the structure of tropical forests in S.E. Asia resulting from human disturbance, even within partially-protected forest, may result in the presence of butterfly assemblages of higher species diversity but of lower biogeographical distinctiveness, and therefore of lower value in terms of the conservation of global biodiversity.

In insects, the outcome of intraspecific competition for food during development depends primarily upon larval density and larval sex, but effects will also depend on the particular trait under consideration and the species under study. Experimental manipulations of larval densities of a Madeiran population of the speckled wood butterfly Pararge aegeria confirmed that intraspecific competition affected growth. As densities increased P. aegeria adults were smaller and larval development periods were longer. Sexes responded differently to rearing density. Females were more adversely affected by high density than males, resulting in females having smaller masses at pupation. Survivorship was significantly higher for larvae reared at low densities. No density effect on adult sex ratios was observed. Intraspecific competition during the larval stage would appear to carry a higher cost for females than males. This may confer double disadvantage since females are dependent on their larval derived resources for reproduction as they have little opportunity to accumulate additional resources as adults. This suggests that shortages of larval food could affect fecundity directly. Males, however, may be able to compensate for a small size by feeding as adults and/or by altering their mate location tactics.

In insects, the outcome of intraspecific competition for food during development depends primarily upon larval density and larval sex, but effects will also depend on the particular trait under consideration and the species under study. Experimental manipulations of larval densities of a Madeiran population of the speckled wood butterfly Pararge aegeria confirmed that intraspecific competition affected growth. As densities increased P. aegeria adults were smaller and larval development periods were longer. Sexes responded differently to rearing density. Females were more adversely affected by high density than males, resulting in females having smaller masses at pupation. Survivorship was significantly higher for larvae reared at low densities. No density effect on adult sex ratios was observed. Intraspecific competition during the larval stage would appear to carry a higher cost for females than males. This may confer double disadvantage since females are dependent on their larval derived resources for reproduction as they have little opportunity to accumulate additional resources as adults. This suggests that shortages of larval food could affect fecundity directly. Males, however, may be able to compensate for a small size by feeding as adults and/or by altering their mate location tactics.

The small helicid snail Hekrostom paupercula occurs in the Azores and Madeira. Previously regarded as a single species, it was split into two genera on the basis of variation in shell morphology and genital anatomy: Heterostoma having a toothed shell and being hemiphallic, while Steenbergzu had a toothless shell and was euphallic. This division was first questioned when toothed shells (Hetcrostomu) in the Azores were found not to be hemiphallic. In this study the genitalia of 361 specimens from islands in the Madeira archipelago were examined. Four components of the genitalia were measured (penislepiphallus, flagellum, bursa stalk and bursa) for 158 individuals. Hemiphally was found to be rare, occurring in only a proportion of the populations at two localities and it did not correspond with the expected shell morphology-the shells were untoothed ( = Steenbergia), which is the opposite of that previously described.Variation in the genitalia was geographically based: Madeira and its nearest neighbour islands forming one group and the Porto Santo islands another. There is no evidence to suggest that the hemiphallic animals are more than an intraspecific form. It is suggested that the variation between the two island groups is reflective of allopatric differentiation. Without further evidence of divergence, H. paupercufa should be regarded as the sole species throughout the range and the genus Steenbergia should be suppressed.

Once mated, the optimal strategy for females of the monandrous butterfly, Pararge aegeria, is to avoid male contact and devote as much time as possible to ovipositing, as there is little advantage for females to engage in multiple matings. In other butterfly species the presence of males during egg laying has been shown to affect aspects of oviposition behavior and it has been suggested that repeated interference from males has the potential to reduce reproductive output. The aim of this study was to assess the effects of male presence during oviposition on reproductive output and behavior of a population of P. aegeria obtained from Madeira Island, Portugal, and maintained in the laboratory. Two experiments were performed where females were housed individually in small cages. Experiment 1 examined how social factors influenced the egg laying behavior of females. To do this the presence or absence of males was manipulated and egg size and number was measured over the first 14 days of oviposition. It was observed that when males were present during oviposition females made a trade-off between egg size and number. Experiment 2 examined how social factors affected oviposition site choice. Again, male presence/absence was manipulated, but in this experiment where the female laid her egg in relation to host quality was scored, and the size of the egg laid was measured. In the absence of males females selectively positioned their larger eggs on good quality host plants. However, selective oviposition was no longer observed when females were in the presence of males. We suggest that P. aegeria females from the Madeira Island population are adapted for a flexible oviposition strategy, governed by external cues, allowing a trade-off between egg size and number when the time available for egg laying is limiting.

Analyses of the habitat distributions and densities of Madeiran and La Gomeran butterflies and birds are used to test the predictions of the taxon cycle hypothesis. The predictions are as follows: recent colonists should occupy more habitats and be found at higher densities than endemic species or sub-species; colonists should predominate in the marginal habitats on the islands.The distributions of Madeiran and La Gomeran birds and butterflies do not conform to those predicted by the taxon cycle. Neither do the densities of the bird and butterfly species on either island. There is some evidence that recent colonizers occupy marginal habitats but we suggest that it is difficult to draw conclusions when man has greatly influenced the nature of the islands' habitats.

Two species of speckled wood butterfly occur in Medeira. Pararge xiphia is endemic and is very similar in morphology, behaviour and general ecology to P. aegeria which was first recorded on the island in 1976. We collected behavioural data on the males of the two species at sites where the indigenous laurel forest meets non‐native forest and agriculture. It is in these areas that the two species are found together in particularly high densities. Male Pararge butterflies defend sunlit areas of vegetation and attempt to exclude other butterflies. If a territorial intruder is a conspecific or the other Pararge species, extended chases or spiraling flights may take place. Interactions between the two Pararge species are longer and more likely to be escalated than those between either species and a range of other butterfly species. Pararge aegeria is more aggressive in its territorial behaviour than P. xiphia and the latter may be suffering more from the interactions. The results demonstrate that the two species are competing for space and therefore, that territorial behaviour could be a mechanism by which interspecific competition could be taking place. Any adaptive explanation for the interspecifc territoriality remains speculative but this recent and probably natural, colonization may provide an excellent opportunity to examine the role of interspecific competition in structuring communities. The arrival of P. aegeria on Madeira has created an almost unique natural experiment, the study of which will potentially avoid many of the problems traditionally associated with the study of competition.