Jukka Suhonen

Immunocompetence, developmental stability and wingspot size in the damselfly Calopteryx splendens L.

Calopteryx splendens males exhibit a remarkable variation in wing pigmentation both within and between populations. In this study, we examined whether the wingspots of male C.splendens are related to male quality. We measured the nylon implant encapsulation rate for 85 males and found that males with larger wingspots had a faster encapsulation rate, indicating a better immunocompetence. We also found that the encapsulation rate was positively correlated with the density of haemocytes in the haemolymph. Another measurement of male quality, fluctuating asymmetry of wingspots, correlated negatively with the size of the wingspots. Males with asymmetrical wingspots also had lower encapsulation rates than more symmetrical males. Our results suggest that the size of wingspot is an indicator of male quality in C.splendens.

Do pheromones reveal male immunocompetence

Pheromones function not only as mate attractors, but they may also relay important information to prospective mates. It has been shown that vertebrates can distinguish, via olfactory mechanisms, major histocompatibility complex types in their prospective mates. However, whether pheromones can transmit information about immunocompetence is unknown. Here, we show that female mealworm beetles (Tenebrio molitor) prefer pheromones from males with better immunocompetence, indicated by a faster encapsulation rate against a novel antigen, and higher levels of phenoloxidase in haemolymph. Thus, the present study indicates that pheromones could transmit information about males parasite resistance ability and may work as a reliable sexual ornament for female choice.

Predation Risk Influences the Use of Foraging Sites by Tits

In coniferous forests of Central Finland, tits (Paridae) and the Goldcrest (Regulus regulus) exploit nonrenewable resources in their group territories during the winter. Results of many studies have indicated that interspecific competition restricts the use of foraging sites in mixed—species winter flocks. However predation is a significant mortality factor in these species, and predation risk might also restrict the selection of foraging sites. The Pygmy Owl (Glaucidium passerinum) is the main diurnal predator of these small passerines during winter. Predation risk from the Pygmy Owl varies greatly with the availability of voles as alternative prey. The purpose of this study is to examine the effects of predation risk on the use of foraging sites in coniferous forest tits during winter. I collected foraging data from Willow (Parus montanus) and Crested Tits (P. cristatus) during one winter when vole populations had crashed and another winter when vole density was high to see if predation risk affects the selection of foraging sites by these species. Both Willow and Crested Tits changed to foraging in the inner parts of coniferous trees after the vole populations had crashed and when the Pygmy Owls started to hunt the tits. Additionally, in both pine and birch Willow Tits moved towards the treetops under high predation risk. Since all the foraging shifts were towards sites that are regarded to be safest from predation risk, it seems that predation risk in addition to interspecific competition influences the use of foraging sites by tits in coniferous forest.

Distribution and habitat selection of wintering birds in urban environments

Habitat selection of wintering land-birds was studied in 31 human settlements in Finland. A total of 26 wintering bird species representing 5155 individuals were observed. Between-year variation (CVB%) and short-term fluctuation within one winter (CVW%) in species richness (CVB=10% CVW=15%) were low, as were total numbers of birds (CVB=22% CVW=24%) and populations of the most common bird species (CVB=20–40% CVW=15–47%). The most abundant bird species (e.g., Passer domesticus, Parus major and Pica pica) occurred in most of the study sites. The total densities of omnivorous birds, sedentary birds and bird species that commonly use feeding tables were higher in a heavily urbanized areas than in moderately or less urbanized areas. According to the Canonical Correspondence Analysis, three corvid species populations, P. domesticus and Columba livia domestica were positively related to human population density. Corvus corone cornix and P. domesticus populations correlated positively with the proportion of the built-up areas in the study plots. The omnivorous diet of these species was a possible reason for their success in urban environments. Dendrocopus major, Parus montanus, Parus cristatus, Parus ater and Certhia familiaris were negatively related to the urbanization axis. These species live mainly in coniferous forest habitats and are probably unable to use deciduous-dominated urban parks in winter time. To attract these species, coniferous trees and shrubs should also be used in park management and planning in northern latitudes. Many species, like Pic. pica, Carduelis chloris and Parus caeruleus, were located at an intermediate place on an urban–forest gradient axis. We suppose that these species are the most probable candidates for colonizing or increasing their abundances in European towns and cities in near the future. All of these species use feeding tables, which help them to adapt to urban environments.

Interspecific aggression and character displacement in the damselfly Calopteryx splendens.

Problems in species recognition are thought to affect the evolution of secondary sexual characters mainly through avoidance of maladaptive hybridization. Another, but much less studied avenue for the evolution of sexual characters due to species recognition problems is through interspecific aggression. In the damselfly, Calopteryx splendens, males have pigmented wing spots as a sexual character. Large‐spotted males resemble males of another species, Calopteryx virgo, causing potential problems in species recognition. In this study, we investigate whether there is character displacement in wing spot size and whether interspecific aggression could cause this pattern. We found first that wing spot size of C. splendens in populations decreased with increasing relative abundance of C. virgo. Secondly, C. virgo males were more aggressive towards large‐ than small‐spotted C. splendens males. Thirdly, in interspecific contests C. virgo males had better territory holding ability than C. splendens males. These results suggest that interspecific aggression may have caused character displacement in wing spot size of C. splendens, because the intensity of aggression towards large‐spotted males is likely to increase with relative abundance of C. virgo males. Thus, interspecific aggression may be an evolutionarily significant force that is able to cause divergence in secondary sexual characters.

AVIAN PREDATION RISK MODIFIES BREEDING BIRD COMMUNITY ON A FARMLAND AREA

In farmland areas of western Finland more than four-fifths of breeding birds are migratory species, mostly small passerines. Migrants arrive at their breeding areas later than their main avian predators, European Kestrels (Falco tinnunculus). We provide ev- idence that avian predators are a major factor modifying the breeding bird assemblage of a large field. The distribution of kestrels (hence, predation) was manipulated using nest boxes, which are the only nesting places in open farmland. We counted birds on nine 25- ha plots in which a kestrel pair bred, and on nine control areas situated > 1000 m from the nearest kestrel nest in large agricultural fields during early summer 1992. We also counted birds on 15 transect lines (length 1000 m, width 100 m) radiating away from kestrel nests. Observations of the hunting behavior of breeding kestrels showed that kestrels mostly captured their prey items 140 g) were independent of the presence of kestrel nests. Skylarks (Alauda arvensis), the most abundant migratory species in the study area, bred less often near kestrel nests than farther away. The results of line transect counts corroborated results of area counts. Our conclusion is that predation risk influences habitat selection of small migratory species in open habitats where scarce vegetative cover gives little protection.

INTERSPECIFIC AGGRESSION CAUSES NEGATIVE SELECTION ON SEXUAL CHARACTERS

Abstract Interspecific aggression originating from mistaken species recognition may cause selection on secondary sexual characters, but this hypothesis has remained untested. Here we report a field experiment designed to test directly whether interspecific aggression causes selection on secondary sexual characters, wing spots, in wild damselfly populations. Males of Calopteryx virgo are more aggressive toward males of C. splendens with large than with small wing spots. This differential interspecific aggression may cause negative selection on wing spot size. Indeed, our results show that directional survival selection on wing spot size of C. splendens males was changed by experimental removal of C. virgo males. Without removal, directional selection went from positive to negative with increasing relative abundance of C. virgo males. In populations where C. virgo males were removed, this relationship disappeared. These results verify that interspecific aggression can cause negative selection on sexual characters. Thus, interspecific aggression has the potential to cause divergence on these characters between two species offering an alternative explanation for reinforcement for generating character displacement in secondary sexual characters.

Interspecific territoriality in Calopteryx damselflies: the role of secondary sexual characters

Interspecific territoriality is usually interpreted to result from interspecific interference competition, although it may also originate from mistaken species recognition. In the latter case, it may be based on similarity of secondary sexual characters. In the damselfly Calopteryx splendens, males have pigmented wing spots as a sexual character, and males with the largest spots resemble males of another species, Calopteryx virgo. Probably because of this resemblance, C. virgo males are more aggressive towards large- than small-spotted C. splendens males. We examined whether wing spot size of C. splendens males affects territorial interactions between the species. In a removal experiment, the number of territorial C. splendens increased after C. virgo males were removed. However, interspecific territoriality was incomplete since before the removal the territories of the species partially overlapped. Wing spot size of C. splendens seemed to affect interspecific territoriality: before the removal territorial and nonterritorial C. splendens males had similar spot sizes and the distance to the nearest C. virgo territory increased with wing spot size of C. splendens. In addition, after the removal of C. virgo, the relation between wing spot size and the distance to the nearest old C. virgo territory disappeared. Our results suggest that mistaken species recognition may account for the interspecific territorial behaviour in the two species. Furthermore, interspecific territoriality may cause negative selection on wing spot size and thus may explain character displacement in wing spot size of C. splendens males.

Predation risk and the organization of the Parus guild

Many studies indicate that interspecific competition restricts the use of foraging sites in mixed-species winter flocks of tits. However, predation is a strong mortality factor for members of the tit guild and predation risk may restrict the selection of foraging sites and organisation of the mixed-species tit flock. We evaluated pygmy owl (Glaucidium passerinum) predation can North European tits and goldcrests. A literature analysis of six areas showed clearly that pygmy owls feed more heavily on those species that forage on exterior tree parts (coal tit P. ater and golderest Regulus regulus)

Selecting networks of nature reserves: methods do affect the long-term outcome

Data on vascular plants of boreal lakes in Finland were used to compare the efficiency of reserve selection methods in representing four aspects of biodiversity over a 63 year period. These aspects included species richness, phylogenetic diversity, restricted range diversity and threatened species. Our results show that the efficiency of reserve selection methods depends on the selection criteria used and on the aspect of biodiversity under consideration. Heuristic methods and optimizing algorithms were nearly equally efficient in selecting lake networks over a small geographical range. In addition, a scoring procedure was observed to be efficient in maintaining different aspects of biodiversity over time. However, the random selection of lakes seems to be the most inefficient option for a reserve network. In general, reserve selection methods seem to favour lakes that maximize one aspect of diversity at the time of selection, but the network may not be the best option for maintaining the maximum diversity over time. The reserve selection methods do affect the long-term outcome but it is impossible to recommend one method over the others unequivocally.