Population structure of a large blue butterfly and its specialist parasitoid in a fragmented landscape

Habitat fragmentation may interrupt trophic interactions if herbivores and their specific parasitoids respond differently to decreasing connectivity of populations. Theoretical models predict that species at higher trophic levels are more negatively affected by isolation than lower trophic level species. By combining ecological data with genetic information from microsatellite markers we tested this hypothesis on the butterfly Maculinea nausithous and its specialist hymenopteran parasitoid Neotypus melanocephalus. We assessed the susceptibility of both species to habitat fragmentation by measuring population density, rate of parasitism, overall genetic differentiation (theta(ST)) and allelic richness in a large metapopulation. We also simulated the dynamics of genetic differentiation among local populations to asses the relative effects of migration rate, population size, and haplodiploid (parasitoid) and diploid (host) inheritance on metapopulation persistence. We show that parasitism by N. melanocephalus is less frequent at larger distances to the nearest neighbouring population of M. nausithous hosts, but that host density itself is not affected by isolation. Allelic richness was independent of isolation, but the mean genetic differentiation among local parasitoid populations increased with the distance between these populations. Overall, genetic differentiation in the parasitoid wasp was much greater than in the butterfly host and our simulations indicate that this difference is due to a combination of haplodiploidy and small local population sizes. Our results thus support the hypothesis that Neotypus parasitoid wasps are more sensitive to habitat fragmentation than their Maculinea butterfly hosts.     

Population modelling of the spatial interactions between Maculinea rebeli their initial foodplant Gentiana cruciata and Myrmica ants within a site

A spatial computer simulation model has been developed to assist our understanding of the ways in which Maculinea butterflies depend upon the spatial distribution and abundance of their initial foodplant and their Myrmica host ant. It was initially derived for the Maculinea rebeli-Myrmica schencki-Gentiana cruciata system. It relates the population processes of the competing host and other ant species to an underlying gradient of habitat quality and incorporates the impact of adopted Maculinea caterpillars on the growth and survival of individual ant nests. The model was initially calibrated for a large site in the Spanish Pyrenees, but has since been successfully tested on 12 French sites and another in Spain. On such sites, with M. rebeli present, there is a close relationship between Maculinea population density and the density of the early larval foodplant G. cruciata. Optimum gentian density is estimated to be about 1500 plants ha-1 on sites with the natural clumping of gentians found. However, any site management which added extra gentians, especially if filling the gaps, is predicted to reduce the Maculinea population. Meta-population studies of single species have shown that the size and spatial arrangement of patches of assumed uniformly suitable habitat can influence their population dynamics and persistence. Our modelling suggests that the spatial pattern of suitable habitat of varied quality within a single site can influence the local butterfly population size and perhaps also persistence. Despite being free-ranging over the whole area, the butterfly's dynamics may depend on the arrangement of habitat quality at a finer spatial scale, due to its interactions with ant species possessing narrower habitat niches and more localized dispersal. © Rapid Science Ltd. 1998     

Strong dispersal in a parasitoid wasp overwhelms habitat fragmentation and host population dynamics

The population dynamics of a parasite depend on species traits, host dynamics and the environment. Those dynamics are reflected in the genetic structure of the population. Habitat fragmentation has a greater impact on parasites than on their hosts because resource distribution is increasingly fragmented for species at higher trophic levels. This could lead to either more or less genetic structure than the host, depending on the relative dispersal rates of species. We examined the spatial genetic structure of the parasitoid wasp Hyposoter horticola, and how it was influenced by dispersal, host population dynamics and habitat fragmentation. The host, the Glanville fritillary butterfly, lives as a metapopulation in a fragmented landscape in the Åland Islands, Finland. We collected wasps throughout the 50 by 70 km archipelago and determined the genetic diversity, spatial population structure and genetic differentiation using 14 neutral DNA microsatellite loci. We compared the genetic structure of the wasp with that of the host butterfly using published genetic data collected over the shared landscape. Using maternity assignment, we also identified full‐siblings among the sampled parasitoids to estimate the dispersal range of individual females. We found that because the parasitoid is dispersive, it has low genetic structure, is not very sensitive to habitat fragmentation and has less spatial genetic structure than its butterfly host. The wasp is sensitive to regional rather than local host dynamics, and there is a geographic mosaic landscape for antagonistic co‐evolution of host resistance and parasite virulence.     

Does diet breadth control herbivorous insect distribution size? Life history and resource outlets for specialist butterflies

Although butterfly distributions are known to be positively correlated with the number of larval hostplants used it is not known to what extent larval hostplant number uniquely influences butterfly distributions and to what extent effects are indirect through other variables. This issue is central to understanding the part generalism and specialism in host use play in organism persistence and conservation. Here, we have modelled the links between larval hostplant number and butterfly distributions using data from the UK. The model identifies the key variables that connect number of hostplants used by butterflies and the size of butterfly distributions. Significant correlations between variables give support to the model. Access to more hostplants is shown to affect a number of resource and life history variables impinging on butterfly population abundances and butterfly distributions. Butterfly distributions are largely accounted for (R²>81%) by a set of resource and life history variables linked to numbers of hostplants: biotope occupancy, nectar sources used, utilities (the number of structures used by each life-cycle stage) and hostplant abundance. Application of partial regression demonstrates that the unique contribution of hostplant number to butterfly distributions is relatively small (R² = 14% to 33%), indicating that host use generalism has a limited direct impact on distributions. The modest correlations linking variables within the model illustrates that specialist phytophage feeders have a number of potential, distinct outlets, via resource and life history variables, to compensate for lack of supplementary larval hosts within their geographical ranges and enabling them to persist. Variables in the model each have considerable independence of action; without this, specialist feeders would have difficulty in expanding their distributions and acquiring new hosts, functionally-linked processes affecting evolutionary dynamics and persistence. We also question the nature of a direct functional link between local population abundance and distributions. Our model suggests a more complex functional relationship with implications for conserving insect herbivores.     

Spatial ecology of host–parasitoid interactions: a threatened butterfly and its specialised parasitoid

Habitat conservation for threatened temperate insect species is often guided by one of two paradigms: a metapopulation approach focusing on patch area, isolation and number; or a habitat approach focusing on maintaining high quality habitat for the focal species. Recent research has identified the additive and interacting importance of both approaches for maintaining populations of threatened butterflies. For specialised host-parasitoid interactions, understanding the consequences of habitat characteristics for the interacting species is important, because (1) specialised parasitoids are particularly vulnerable to the consequences of fragmentation, and (2) altered interaction frequencies resulting from changes to habitat management or the spatial configuration of habitat are likely to have consequences for host dynamics. The spatial ecology of Cotesia bignellii, a specialist parasitoid of the threatened butterfly Euphydryas aurinia, was investigated at two spatial scales: within habitat patches (at the scale of individual aggregations of larvae, or ‘webs’) and among habitat patches (the scale of local populations). Parasitism rates were investigated in relation to larval web size, vegetation sward height and host density. Within patches, the probability of a larval webs being parasitized increased significantly with increasing number of larvae in the web, and parasitism rates increased significantly with increasing web isolation. The proportion of webs parasitized was significantly and negatively correlated with cluster density. Among habitat patches the proportion of parasitized webs decreased as cluster density increased. Clusters with a high proportion of larval webs parasitized tended to have lower parasitism rates per larval web. These results support the call for relatively large and continuous habitat patches to maintain stable parasitoid and host populations. Conservation efforts directed towards maintenance of high host plant density could allow E. aurinia to reduce parasitism risk, while providing C. bignellii with sufficient larval webs to allow population persistence.     

Coevolutionary fine-tuning: evidence for genetic tracking between a specialist wasp parasitoid and its aphid host in a dual metapopulation interaction

In the interaction between two ecologically-associated species, the population structure of one species may affect the population structure of the other. Here, we examine the population structures of the aphid Metopeurum fuscoviride, a specialist on tansy Tanacetum vulgare, and its specialist primary hymenopterous parasitoid Lysiphlebus hirticornis, both of which are characterized by multivoltine life histories and a classic metapopulation structure. Samples of the aphid host and the parasitoid were collected from eight sites in and around Jena, Germany, where both insect species co-occur, and then were genotyped using suites of polymorphic microsatellite markers. The host aphid was greatly differentiated in terms of its spatial population genetic patterning, while the parasitoid was, in comparison, only moderately differentiated. There was a positive Mantel test correlation between pairwise shared allele distance (DAS) of the host and parasitoid, i.e. if host subpopulation samples were more similar between two particular sites, so were the parasitoid subpopulation samples. We argue that while the differences in the levels of genetic differentiation are due to the differences in the biology of the species, the correlations between host and parasitoid are indicative of dependence of the parasitoid population structure on that of its aphid host. The parasitoid is genetically tracking behind the aphid host, as can be expected in a classic metapopulation structure where host persistence depends on a delay between host and parasitoid colonization of the patch. The results may also have relevance to the Red Queen hypothesis, whereupon in the 'arms race' between parasitoid and its host, the latter 'attempts' to evolve away from the former.     

Metapopulation viability analysis of the bog fritillary butterfly using RAMAS/GIS

Many species living in man-shaped landscapes are restricted to small natural habitat patches and form metapopulations; predicting their future is a central issue in applied ecology. We examined the viability of the bog fritillary butterfly Proclossiana eunomia Esper, a specialist glacial relict species, in a highly fragmented landscape (<1% of suitable habitat in 10 km²), by way of population viability analysis. We used comprehensive data from a long-term study in which a patchy population was monitored during ten consecutive years to parameterise a spatially structured metapopulation model using commercially available platform RAMAS/GIS 3.0. Population growth rate was density-dependent and modulated by various climatic variables acting on different developmental stages of the butterfly. Density dependence was probably related to larval parasitism by a specific parasitoid. Population size was negatively affected by an increase in the mean temperature. Dispersal was modelled as the observed proportion of movements between patches, taking into account the probability of emigration out of a given patch. Our model provided results close to the picture of the system drawn from the field data and was considered as useful in making predictions about the metapopulation. Demographic parameters proved to have a far higher impact on metapopulation persistence than dispersal or correlation of local dynamics. Scenarios simulating both global warming and management of habitat patches by rustic herbivore grazing indicated a decrease in the viability of the metapopulation. Our results prompted the regional nature conservation agency to modify the planned management regime. We urge conservation biologists to use structured population models including local population dynamics for viability analysis targeted to such threatened metapopulations in highly fragmented landscapes.     

Resource use of specialist butterflies in agricultural landscapes: conservation lessons from the butterfly Phengaris (Maculinea) nausithous

Most of the European grassland butterfly species are dependent on species rich grasslands shaped by low intensity farming. Conservation of these specialist species in agricultural landscapes relies on knowledge of their essential resources and the spatial distribution of these resources. In The Netherlands, the dusky large blue Phengaris (Maculinea) nausithous butterflies were extinct until their reintroduction in 1990. In addition, a spontaneous recolonization of road verges in an agricultural landscape occurred in 2001 in the southern part of The Netherlands. We analyzed the use of the essential resources, both host plants and host ants, of the latter population during the summers of 2003 and 2005. First we tested whether the distribution of the butterflies during several years could be explained by both the presence of host plants as well as host ants, as we expected that the resource that limits the distribution of this species can differ between locations and over time. We found that oviposition site selection was related to the most abundant resource. While in 2003, site selection was best explained by the presence of the host ant Myrmica scabrinodis, in 2005 it was more strongly related to flowerhead availability of the host plant. We secondly compared the net displacement of individuals between the road verge population and the reintroduced population in the Moerputten meadows, since we expected that movement of individuals depends on the structure of their habitat. On the road verges, butterflies moved significantly shorter distances than on meadows, which limits the butterflies in finding their essential resources. Finally we analyzed the availability of the two essential resources in the surroundings of the road verge population. Given the short net displacement distances and the adverse landscape features for long-distance dispersal, this landscape analysis suggests that the Phengaris population at the Posterholt site is trapped on the recently recolonized road verges. These results highlight the importance of assessing the availability of essential resources across different years and locations relative to the movement of the butterflies, and the necessity to careful manage these resources for the conservation of specialist species in agricultural landscapes, such as this butterfly species.     

Causes and consequences of small population size for a specialist parasitoid wasp

The parasitoid wasp Cotesia melitaearum lives in extremely small extinction-prone populations in the Åland islands of southwest Finland. Intensive observational data from two generations, a laboratory competition experiment, and 8 years of survey data were used to measure the causes, extent and consequences of small population size for this parasitoid. In the spring generations of 1999 and of 2000 we observed 21 out of 23 and 26 populations respectively, ranging in size from 2 to 103 parasitoid cocoons. Within these populations the fraction of individuals surviving to adulthood decreased with increasing parasitoid population size. The largest source of mortality was predation (44%) followed by parasitism (20%) and unknown causes (10%). In the field about 30% of the host butterfly larvae are parasitized by a competing parasitoid, Hyposoter horticola. A laboratory competition experiment showed that C. melitaearum eggs died when laid in post-diapause host larvae occupied by H. horticola. Consequently one-third of the progeny of the over-wintering generation of C. melitaearum from the field die as a result of larval competition. The survey of host and parasitoid population dynamics over 8 years showed that extinction of local host butterfly populations occupied by the parasitoid was not associated with current parasitoid population size. Over the same period small parasitoid populations were more likely to become extinct than large populations. However, parasitoid population size was not related to parasitoid extinction when the host also became extinct. These data suggest that the parasitoid populations are kept small through the action of natural enemies and competitors, some of which are density dependent. Local populations are so small that they become extinct frequently and rarely measurably affect the population dynamics of their host. It is likely that this parasitoid persists in Åland because of the spatial asynchrony of local population dynamics.     

Habitat utilization of the Glanville fritillary butterfly in the Tianshan Mountains, China, and its implication for conservation

In 2004 and 2005, we investigated the distribution of the Glanville fritillary butterfly (Melitaea cinxia) and its host plant in the Tianshan Mountains of China, in order to clarify its habitat utilization. Female butterflies were almost captured on dry meadows on slopes, where plenty of host plant (Veronica spicata) is distributed. Although there are host plants on meadows at higher altitude (>2,050 m), no butterfly was found there. Among the meadows with host plants, a patch of dry meadow (newly-found meadow) was considered as a natal site because of the high density and freshness of butterflies. Unlike females, male butterflies were almost captured in valleys, where there are no host plants and fewer nectar plants. It might be related to specific mating system of M. cinxia in the study site, or specific environmental factors. Thus valleys are important habitat for males. Although the status of M. cinxia is yet unknown in China, we give some suggestions for conservation based on this study. First, dry meadows with host plants are the essential component for persistence of M. cinxia, among which the specific sites with more favourable conditions, such as natal site, are most important. Second, as a site with adult resource requirement, valleys should be included as part of the habitat of the butterfly. Finally, meadows at higher altitude are not utilized at present but they are potential habitats which need to be maintained for any shifts in altitudinal range in response to global warming in the future. Hence, the trade-off of present cost and future benefit should be taken into account when formulating a conservation strategy for M. cinxia in the Tianshan Mountains of China.     

Do distances among host patches and host density affect the distribution of a specialist parasitoid?

The effect of spatial habitat structure and patchiness may differ among species within a multi-trophic system. Theoretical models predict that species at higher trophic levels are more negatively affected by fragmentation than are their hosts or preys. The absence or presence of the higher trophic level, in turn, can affect the population dynamics of lower levels and even the stability of the trophic system as a whole. The present study examines different effects of spatial habitat structure with two field experiments, using as model system the parasitoid Cotesia popularis which is a specialist larval parasitoid of the herbivore Tyria jacobaeae. One experiment examines the colonisation rate of the parasitoid and the percentage parasitism at distances occurring on a natural scale; the other experiment examines the dispersal rate and the percentage parasitism in relation to the density of the herbivore and its host plant. C. popularis was able to reach artificial host populations at distances up to the largest distance created (at least 80 m from the nearest source population). Also, the percentage parasitism did not differ among the distances. The density experiment showed that the total number of herbivores parasitised was higher in patches with a high density of hosts, regardless of the density of the host plant. The percentage parasitism, however, was not related to the density of the host. The density of the host plant did have a (marginally) significant effect on the percentage parasitism, probably indicating that the parasitoid uses the host plant of the herbivore as a cue to find the herbivore itself. In conclusion, the parasitoid was not affected by the spatial habitat structure on spatial scales that are typical of local patches.     

High and dry or sunk and dunked: lessons for tallgrass prairies from quaking bogs

Northern Wisconsin bogs provide a natural experiment on butterfly population occurrence in a naturally highly fragmented vegetation type, which may provide insight on conserving butterflies in anthropogenically fragmented and degraded landscapes. We surveyed butterflies in bogs (about as unaffected by humans as possible, but naturally occurring over <1% of northern Wisconsin) primarily during 2002?C2009, with additional observations from 1986 to 2001. Different bog types had different bog-specialist butterfly faunas, but bog butterfly abundance also differed in similar vegetations among subregions. Some small isolated bogs held very high densities of specialist butterflies. Summer but not spring specialists frequented adjacent lowland roadsides and utilized a variety of non-native as well as native nectar sources. Paleo-entomology indicates that insects don??t evolve out of trouble; instead they move out of trouble. Given the low dispersal apparent today for species restricted to bogs, ??move?? might be better understood as ??hunkering?? within their vegetation as it expands and shrinks and moves around the landscape. Although bogs appeared to have more intact specialist butterfly faunas than tallgrass prairies (99.9% destroyed by human activities), bog butterflies do not live in average sites even in a relatively natural landscape. Just as bog butterflies are ??sunk and dunked?? in isolation, specialist butterflies elsewhere may have been left ??high and dry?? naturally, or are now due to human activities. Numerous studies have demonstrated that presence and abundance of specialist butterflies increase with increasing size and connectedness of habitat patches. But with long-term consistent vegetation, populations with high abundances in small isolated sites and with low numbers thinly occurring in large sites can be secure, as shown by bog butterflies.     

The impact of habitat fragmentation on trophic interactions of the monophagous butterfly <Emphasis Type="Italic">Polyommatus coridon</Emphasis>

Theory predicts that habitat fragmentation, including reduced area and connectivity of suitable habitat, changes multitrophic interactions. Species at the bottom of trophic cascades (host plants) are expected to be less negatively affected than higher trophic levels, such as herbivores and their parasitoids or predators. Here we test this hypothesis regarding the effects of habitat area and connectivity in a trophic system with three levels: first with the population size of the larval food plant Hippocrepis comosa, next with the population density of the monophagous butterfly species Polyommatus coridon and finally with its larval parasitism rate. Our results show no evidence for negative effects of habitat fragmentation on the food plant or on parasitism rates, but population density of adult P. coridon was reduced with decreasing connectivity. We conclude that the highly specialized butterfly species is more affected by habitat fragmentation than its larval food plant because of its higher trophic position. However, the butterfly host species was also more affected than its parasitoids, presumably because of lower resource specialization of local parasitoids which also frequently occur in alternative hosts. Therefore, conservation efforts should focus first on the most specialized species of interaction networks and second on higher trophic levels.     

Analysis of genetic diversity in a peatland specialist butterfly suggests an important role for habitat quality and small habitat patches

Understanding effects of habitat and landscape features on genetic variation is a prerequisite for the development of habitat and landscape management strategies aimed at conserving genetic diversity. While there has been considerable research on the effects of landscape structure on the genetics of populations, a recent review identified key biases in this body of work. The majority of landscape genetic studies investigate the intervening matrix’s influence on differentiation and gene flow among populations. Although characteristics of local habitat patches may be important determinants of genetic diversity, fewer studies have examined these relationships. Here we use node- and neighbourhood-based approaches to analyze correlates of genetic diversity in the bog copper (Lycaena epixanthe), a specialist butterfly endemic to temperate Nearctic peatlands that is threatened in parts of its range. Based on 190 repeatable and polymorphic amplified fragment length polymorphism loci, we found that genetic diversity was higher in habitat patches that were smaller and surrounded by more open water. Our results indicate that valuing small peatlands and preserving the surrounding water table may be important for conservation of genetic diversity in this highly specialized species. Our study highlights the importance of variables affecting habitat quality for conservation genetics.     

Effects of parasitoid community structure upon the population dynamics of the honeysuckle leafminer,Chromatomyia suikazurae (Diptera: Agromyzidae)

Population dynamics of a leafminer,Chromatomyia suikazurae (Agromyzidae, Diptera) and its parasitoid community were studied for ten years at seven natural populations along an altitudinal gradient in Japan. This species which mines leaves of a forest shrub,Lonicera gracilipes (Caprifoliaceae), was attacked by 25 hymenopterous parasitoid species. Annually, the parasitoid community structure varied less within a population than among populations. The seven parasitoid communities were clustered into three groups corresponding to the altitudinal gradient: (a) lowland communities dominated by late-attacking, generalist pupal idiobiont eulophids and with highest species diversity, (b) hillside communities dominated by an early-attacking, specialist larval-pupal koinobiont braconid and (c) highland communities dominated by an early-attacking, generalist larval idiobiont eulophid. Annual changes of the host larval densities among the local populations were largely synchronous rather than cyclic. Among these populations, host density levels and mortality patterns greatly varied. By analyzing these inter-populational differences of host mortality patterns, the following conclusions were drawn: (1) The host mortality patterns were determined by the host utilization patterns of the locally dominant species. (2) The host pupal mortality but not larval mortality was related to species diversity but not to species richness itself of each parasitoid community. (3) Density dependence was detected only in pupal mortality at a lowland population dominated by late-attacking pupal parasitoids. These results suggest that interspecific interactions of parasitoids add additive effects to host population dynamics dissimilarly among local populations with different parasitoid communities.     

Regulation of host diapause by an insect parasitoid

Abstract. 1. The interaction between larval development and parasitism by the braconid wasp Cotesia koebelei (Riley), was investigated in a population of the butterfly Euphydryas editha (Boisduval) (Nymphalidae). In this population, the butterfly host has an obligatory overwintering larval diapause.
2. It was found that E. editha larvae harbouring parasitoids were more likely to pass through an extra feeding instar before entering diapause than were non-parasitized conspecifics.
3. In addition, some individuals that were experimentally exposed to multiple parasitoid attacks bypassed diapause completely; these larvae passed through five or six feeding instars, reaching sizes typical of final instar post-diapause larvae.
4. The observed effect of superparasitism occurred regardless of whether the host larvae subsequently produced mature parasitoids, suggesting that parasitoid attack is sufficient to invoke the response.
5. It is proposed that the parasitoid C.koebelei regulates the number of pre-diapause feeding instars of its insect host E. editha, and that some component of the female venom, injected at oviposition, is responsible for this regulation.     

Dispersal, distribution, patch network and metapopulation dynamics of the dingy skipper butterfly (Erynnis tages)

Two general approaches have usually been taken towards understanding the distributions and dynamics of localised species in heterogeneous landscapes, namely habitat characterisation and metapopulation dynamics. We show how habitat and metapopulation dynamics interact to generate a highly localised distribution of a butterfly, despite the extremely widespread nature of the butterfly’s host plant. Egg placement, macro-habitat requirements and dispersal were studied for the butterfly Erynnis tages, in North Wales, where it shows a restricted distribution relative to that of its host plant, Lotus corniculatus. Females laid eggs disproportionately on large plants growing in hollows, with intermediate cover of bare ground and high cover of L. corniculatus. Ideal macro-habitat, studied at 100-m grid resolution, consisted of areas with high host plant densities, sheltered from wind, with light or no grazing or cutting. These specialised conditions are represented as localised patches in the landscape, and define the potential habitat network, within which metapopulation dynamics take place. Although there was a moderate (22%) level of exchange of individual E. tages among local populations, the total number of potential colonists in the whole system was low because source population sizes were small (≤200 individuals at peak in any site in 1997 and 1998). Four unoccupied but apparently suitable 500-m grid squares were colonised between 1997 and 1998, and isolated habitat was less likely to be occupied. Overall, our study suggests that long-term regional persistence of E. tages is very likely to depend on metapopulation processes within the restricted patch network, rather than on the long-term survival of local populations. Received: 25 May 1999 / Accepted: 9 August 1999     

Persistence in Massachusetts of the veined white butterfly due to use of the invasive form of cuckoo flower

The native pierid butterfly Pieris oleracea underwent a large range reduction in New England in the twentieth century, likely due to the introduction the invasive butterfly Pieris rapae (Lep.: Pieridae) to North America in 1860, and later the oligophagous parasitoid Cotesia glomerata (Hymenoptera: Braconidae) in 1884. Thought extirpated from the state by the 1970s, one large dense population of the butterfly was found in the mid 1980s in a flood plain meadow along the Housatonic River in Lenox, Berkshire Co., Massachusetts. We examined how this native pierid was able to maintain a relatively dense local population by feeding on a novel, invasive host plant, Cardamine pratensis (cuckoo flower), in a meadow habitat despite known parasitoid presence. We approached this question in three ways. First, we deployed trap host plants (cuckoo flower and collards) stocked host larvae (first and second instars of either P. rapae or P. oleracea) at the Lenox site and other locations to determine current rates of C. glomerata attack, for comparison with historical information. Second, we used olfactometer experiments to determine if C. glomerata females could detect the cuckoo flower volatiles released during P. oleracea larval feeding. Third, we used field-cage experiments to determine if the plant architecture found in the flood plain meadow inhibited the ability of C. glomerata females to locate and parasitize hosts. Specifically, we asked if overtopping vegetation prevented or reduced parasitism of P. oleracea larvae feeding on the covered basal rosettes of C. pratensis, which is the physical form of host plant for three of the four butterfly generations at the site.     

Life history and population size variability in a relict plant. Different routes towards long-term persistence

A central tenet of conservation biology is that population size affects the persistence of populations. However, many narrow endemic species combine small population ranges and sizes with long persistence, thereby challenging this tenet. I examined the performance of three different-sized populations of Petrocoptis pseudoviscosa (Caryophyllaceae), a palaeoendemic rupicolous herb distributed along a small valley in the Spanish Pyrenees. Reproductive and demographic parameters were recorded over 6 years, and deterministic and stochastic matrix models were constructed to explore population dynamics and extinction risk. Populations differed greatly in structure, fecundity, recruitment, survival rate, and life span. Strong differentiation in life-history parameters and their temporal variability resulted in differential population vulnerability under current conditions and simulated global changes such as habitat fragmentation or higher climatic fluctuations. This study provides insights into the capacity of narrow endemics to survive both at extreme environmental conditions and at small population sizes. When dealing with species conservation, the population size–extinction risk relationship may be too simplistic for ancient, ecologically restricted organisms, and some knowledge of life history may be most important to assess their future.