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ABSTRACT: We examined the long-term, 15-year pattern of population change in a network of 21 Rocky Mountain populations of Parnassius smintheus butterflies in response to climatic variation. We found that winter values of the broadscale climate variable, the Pacific Decadal Oscillation (PDO) index, were a strong predictor of annual population growth, much more so than were endogenous biotic factors related to population density. The relationship between PDO and population growth was nonlinear. Populations declined in years with extreme winter PDO values, when there were either extremely warm or extremely cold sea surface temperatures in the eastern Pacific relative to that in the western Pacific. Results suggest that more variable winters, and more frequent extremely cold or warm winters, will result in more frequent decline of these populations, a pattern exacerbated by the trend for increasingly variable winters seen over the past century.
Ecology 01/2013; 94(1):190-9. · 4.85 Impact Factor
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Journal of the Lepidopterists' Society 06/2012; 66(2):111-113. · 0.27 Impact Factor
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ABSTRACT: Climate change is occurring and insects are responding. Current challenges for ecologists and managers are predicting how organisms will respond to continuing climate change and determining how to mitigate potential negative effects. In contrast to broad scale predictions for climate change involving the distribution of species, in this article we highlight the many ways in which local populations of the Rocky Mountain Apollo butterfly (Parnassius smintheus Doubleday) are predicted to respond to climate change. Using experimental and observational data collected over the past 15 years, we detail both direct and indirect effects. In addition, we identify limitations in our knowledge restricting the ability to predict how populations will respond to climate change. Some changes, such as warmer winter temperatures, may have beneficial effects; however, most of the effects of climate change will be detrimental. Variability in snow cover during the overwintering period and habitat loss due to forest encroachment have the largest potential negative effects.
Insect Science 01/2011; 18:385-392. · 1.10 Impact Factor
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ABSTRACT: Rising treeline threatens the size and contiguity of alpine meadows worldwide. As trees encroach into previously open habitat, the movement and population dynamics of above-treeline alpine species may be disrupted. This process is well documented in studies of the Rocky Mountain apollo butterfly (Parnassius smintheus). However, subtler consequences of treeline rise remain poorly understood. In this study, we examine whether treeline proximity affects feeding behaviour of P. smintheus larvae, due to altered habitat affecting the distribution and availability of their host plant, lance-leaved stonecrop (Sedum lanceolatum). Understanding differential larval exploitation of food resources in relation to the treeline is an important step in predicting the consequences of continued treeline rise. Parnassius smintheus larvae feed more intensively on S. lanceolatum away from the treeline despite the relative paucity of hosts in these areas, and despite higher fitness penalties associated with the plant's herbivory-induced chemical defenses. Sedum lanceolatum growing near the treeline is less attractive, and therefore represents a less significant resource for P. smintheus larvae than its abundance might imply. If treeline rise continues, we suggest that this pattern of altered resource exploitation may represent a mechanism by which larvae are adversely affected even while adult movement among and within meadows appears sufficient for maintaining population health, and total host availability seems ample.
Oecologia 12/2010; 166(1):151-9. · 3.41 Impact Factor
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ABSTRACT: While many studies have examined factors potentially impacting the rate of local population extinction, few experimental studies have examined the consequences of extinction for spatial population dynamics. Here we report results from a large-scale, long-term experiment examining the effects of local population extinction for the dynamics of surrounding populations. From 2001–2008 we removed all adult butterflies from two large, neighboring populations within a system of 17 subpopulations of the Rocky Mountain Apollo butterfly, Parnassius smintheus. Surrounding populations were monitored using individual, mark–recapture methods. We found that population removal decreased immigration to surrounding populations in proportion to their connectivity to the removed populations. Correspondingly, within-generation population abundance declined. Despite these effects, we saw little consistent impact between generations. The extinction rates of surrounding populations were unaffected and local population growth was not consistently reduced by the lack of immigration. The broader results show that immigration affects local abundance within generations, but dynamics are mediated by density-dependence within populations and by broader density-independent factors acting between generations. The loss of immigrants resulting from extinction has little impact on the persistence of local populations in this system.
Oikos 06/2010; 119(12):1961 - 1969. · 3.06 Impact Factor
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ABSTRACT: Spatial population theory predicts that synchrony in the dynamics of local populations should decrease as dispersal among populations decreases. Thus, it would be expected that the extinction of local populations and the attendant loss of immigrants to surrounding populations would reduce synchrony. We tested this hypothesis through a large-scale experiment, simulation of the experimental system and general models. Experimental removal of two adjacent subpopulations of the Rocky Mountain Apollo butterfly, Parnassius smintheus within a network consisting of 15 other local populations resulted in a decrease in immigration to surrounding populations that was proportional to their connectivity to the removal populations. These populations also showed a significant increase in synchrony during population removal. The spatial extent of the synchrony showed good agreement with the predicted loss of immigrants owing to the removals. Simulation of the Parnassius system showed a similar short-term result and also indicated that permanent loss of populations produces structural changes increasing synchrony. General models indicate that an increase in synchrony following extinction occurs when populations undergoing extinction have different carrying capacities than surrounding populations. The result is not owing to biased migration per se, but rather is because of the number of immigrants relative to the carrying capacity. Synchrony following extinction should be most common for patchy populations, but can occur in any situation where carrying capacities differ. Overall, our results indicate that local extinction can create a positive feedback for extinction risk, increasing the probability of extinction for population networks by synchronizing their dynamics.
Proceedings of the Royal Society B: Biological Sciences 11/2009; 277(1682):729-37. · 5.41 Impact Factor
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ABSTRACT: Sympatric insect species that do not share sex pheromone components but have a common host and overlapping adult flight periods are potential targets for the development of a combined sex pheromone-based monitoring tool. A system using a single synthetic pheromone blend in a single lure to bait a single trap to monitor two pests simultaneously represents a novel approach. In this study, a combined pheromone-based monitoring system was developed for two lepidopterous defoliators of trembling aspen Populus tremuloides Michenaux in western Canada, Malacosoma disstria Hübner (Lepidoptera: Lasoicampidae) and Choristoneura conflictana (Walker) (Lepidoptera: Tortricidae). Efficacy and longevity of a lure containing both species' pheromones were tested. Immature stages of each species were sampled to evaluate the ability of pheromone traps baited with the combined lure to predict population density. The combined lure was as attractive to M. disstria and C. conflictana males as were traps baited with each species' pheromone alone. Lure age had no effect on attraction of male C. conflictana to the combined lure but had a negative effect on attraction of M. disstria. The number of male moths captured in traps baited with the combined lure was related to immature counts for both species. Pupal counts of M. disstria and larval counts of C. conflictana provided the best relationships with male captures. The combined lure does not attract M. disstria males in direct proportion to population density, because trap catch was comparatively low at high-density M. disstria sites.
Environmental Entomology 05/2009; 38(2):459-71. · 1.56 Impact Factor
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ABSTRACT: We investigate the effect of parasitoid phenology on host-parasitoid population cycles. Recent experimental research has shown that parasitized hosts can continue to interact with their unparasitized counterparts through competition. Parasitoid phenology, in particular the timing of emergence from the host, determines the duration of this competition. We construct a discrete-time host-parasitoid model in which within-generation dynamics associated with parasitoid timing is explicitly incorporated. We found that late-emerging parasitoids induce less severe, but more frequent, host outbreaks, independent of the choice of competition model. The competition experienced by the parasitized host reduces the parasitoids' numerical response to changes in host numbers, preventing the 'boom-bust' dynamics associated with more efficient parasitoids. We tested our findings against experimental data for the forest tent caterpillar (Malacosoma disstria Hübner) system, where a large number of consecutive years at a high host density is synonymous with severe forest damage.
Theoretical Population Biology 04/2009; 75(2-3):201-15. · 1.65 Impact Factor
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ABSTRACT: We examined the effects of isolation and site size on the abundance, density, emigration and immigration of the butterfly Parnassius smintheus in a series of sub-alpine meadows. Site size was measured either as habitat area or as number of host plants within each meadow. This distinction allowed us to test the hypothesis that population density measured over area (a generalized individuals-area relationship) should tend to decrease with increasing area due to inclusion of more ‘non-habitat’ in larger areas. In general, area measured either as meadow area or host plant abundance explained little deviance in butterfly abundance or movement. Immigration increased with the connectivity (the inverse of isolation) of meadows. We found that individuals-area relationships defined over meadow area showed patterns of decreasing butterfly density with increasing meadow area. This pattern was partially generated by a trend for host plant density to decrease with increasing meadow area. However, this trend was not universal as some small meadows had similar host plant densities to large meadows. Decreasing density with increasing meadow area primarily arose due to decreasing butterfly density with increasing host plant abundance, indicating that multiple mechanisms can produce decreasing population density with increasing area.
American Midland Naturalist 01/2009; · 0.62 Impact Factor
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ABSTRACT: 1. Reproductive asynchrony, where individuals in a population are short-lived relative to the population-level reproductive period, has been identified recently as a theoretical mechanism of the Allee effect that could operate in diverse plant and insect species. The degree to which this effect impinges on the growth potential of natural populations is not yet well understood. 2. Building on previous models of reproductive timing, we develop a general framework that allows a detailed, quantitative examination of the reproductive potential lost to asynchrony in small natural populations. 3. Our framework includes a range of biologically plausible submodels that allow details of mating biology of different species to be incorporated into the basic reproductive timing model. 4. We tailor the parameter estimation methods of the full model (basic model plus mating biology submodels) to take full advantage of data from detailed field studies of two species of Parnassius butterflies whose mating status may be assessed easily in the field. 5. We demonstrate that for both species, a substantial portion of the female population (6.5-18.6%) is expected to die unmated. These analyses provide the first direct, quantitative evidence of female reproductive failure due to asynchrony in small natural populations, and suggest that reproductive asynchrony exerts a strong and largely unappreciated influence on the population dynamics of these butterflies and other species with similarly asynchronous reproductive phenology.
Journal of Animal Ecology 08/2008; 77(4):746-56. · 4.94 Impact Factor
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ABSTRACT: Over the past 50 years, the rising tree line along Jumpingpound Ridge in the Rocky Mountains of Alberta, Canada, has reduced the area of alpine meadows and isolated populations that reside within them. By analyzing an 11-year data set of butterfly population sizes for 17 subpopulations along the ridge, we show that forest habitat separating alpine meadows decouples the dynamics of populations of the alpine butterfly Parnassius smintheus. Although the distance between populations is often negatively correlated with synchrony of dynamics, here we show that distance through forest, not Euclidean distance, determines the degree of synchrony. This effect is consistent with previous results demonstrating that encroaching forest reduces dispersal among populations and reduces gene flow. Decoupling dynamics produces more smaller independent populations, each with greater risk of local extinction, but decoupling may produce a lower risk of regional extinction in this capricious environment.
Proceedings of the National Academy of Sciences 09/2007; 104(34):13702-4. · 9.68 Impact Factor
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ABSTRACT: Migration is a key process for spatially structured populations. We examined how a variety of patch based metrics commonly used to predict the number of immigrants to a habitat patch performed based on data from three different years, in two distinct insect systems. The first system was an herbivorous beetle inhabiting patches of its host plant within a ‘typical’ patch network. In this system there were numerous patches located relatively close to one another, given the beetle's dispersal ability. The second system consisted of a butterfly inhabiting a series of 17 subalpine meadows. Here, the patches were arranged in a linear fashion and were more distant from each other. Overall, we found that the best models incorporating aspects of patch size and/or isolation explained a large (30–40%) amount of deviance in immigration, but there were considerable differences between the systems. For the first system, we found that metrics including the size of the target patch explained the highest proportion of deviance in immigrant numbers, while metrics based only on interpatch distances explained very little deviance. The situation was reversed for the second system. Metrics including the size of the target patch explained little deviance, while metrics based on the distance between patches explained the bulk of deviance in the number of immigrants. The results of our study show that the effects of patch size and isolation on the number of immigrants are highly important, but dependent on spatial scale, the organism studied, and how it responds to the spatial arrangement of patches. Correspondingly, there will be no single generalized metric to predict immigration for all cases. Given the dependency of the results on the system studied, we recommend that future studies provide explicit data on habitat areas and dispersal distance relative to interpatch distance to allow for meaningful comparison among organisms and systems.
Oikos 10/2005; 111(2):359 - 367. · 3.06 Impact Factor
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ABSTRACT: Levels of gene flow among populations vary both inter- and intraspecifically, and understanding the ecological bases of variation in levels of gene flow represents an important link between the ecological and evolutionary dynamics of populations. The effects of habitat spatial structure on gene flow have received considerable attention; however, most studies have been conducted at a single spatial scale and without background data on how individual movement is affected by landscape features. We examined the influence of habitat connectivity on inferred levels of gene flow in a high-altitude, meadow-dwelling butterfly, Parnassius smintheus. For this species, we had background data on the effects of landscape structure on both individual movement and on small-scale population genetic differentiation. We compared genetic differentiation and patterns of isolation by distance, based on variation at seven microsatellite loci, among three regions representing two levels of connectivity of high-altitude, nonforested habitats. We found that reduced connectivity of habitats, resulting from more forest cover at high altitudes, was associated with greater genetic differentiation among populations (higher estimated FST), a breakdown of isolation by distance, and overall lower levels of inferred gene flow. These observed differences were consistent with expectations based on our knowledge of the movement behaviour of this species and on previous population genetic analyses conducted at the smaller spatial scale. Our results indicate that the role of gene flow may vary among groups of populations depending on the interplay between individual movement and the structure of the surrounding landscape.
Molecular Ecology 07/2005; 14(7):1897-909. · 5.52 Impact Factor
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ABSTRACT: Habitat fragmentation is a ubiquitous by-product of human activities that can alter the genetic structure of natural populations, with potentially deleterious effects on population persistence and evolutionary potential. When habitat fragmentation results in the subdivision of a population, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulation, random genetic drift then leads to the erosion of genetic diversity from within the resulting subpopulations and greater genetic divergence among them. Theoretical and simulation analyses predict that these two main genetic effects of fragmentation, greater differentiation among resulting subpopulation and reduced genetic diversity within them, will proceed at very different rates. Despite important implications for the interpretation of genetics data from fragmented populations, empirical evidence for this phenomenon has been lacking. In this analysis, we carry out an empirical study in population of an alpine meadow-dwelling butterfly, which have become fragmented increasing forest cover over five decades. We show that genetic differentiation among subpopulations (G(ST)) is most highly correlated with contemporary forest cover, while genetics diversity within subpopulation (expected heterozygosity) is better correlated with the spatial pattern of forest cover 40 years in the past. Thus, where habitat fragmentation has occurred in recent decades, genetic differentiation among subpopulation can be near equilibrium while contemporary measures of within subpopulation diversity may substantially overestimate the equilibrium values that will eventually be attained.
Proceedings of the Royal Society B: Biological Sciences 04/2005; 272(1562):553-60. · 5.41 Impact Factor
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ABSTRACT: We experimentally examined edge effects and movement patterns of the butterfly Parnassius smintheus in two habitat types, its preferred meadow habitat, and intervening forest matrix habitat. We followed the movement of 46 butterflies released at either 5 or 20m from a forest edge in either forest or meadow habitat. In contrast to theoretical predictions, we found that butterflies flew less frequently, shorter distances, and at lower rates in matrix habitat than they did in meadow habitat. Distance from the edge had little effect on these aspects of movement. Flight was strongly influenced by light levels with butterflies flying more readily at higher light levels. Light levels were higher in meadows than in forest explaining much of the difference in movement patterns. Turning angles showed that butterflies flying in meadow habitat avoided forest edges and that this effect extended nearly 25 m into meadows. Analysis of net displacement from the forest edge reinforced this result and showed that there may be attraction to the meadow for butterflies flying within forest.
Landscape Ecology 01/2005; 20(2):127-135. · 3.06 Impact Factor
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ABSTRACT: Abstract 1. Nectar flower abundance was manipulated through flower removal, and sex ratio was manipulated by moving individual butterflies within a series of nine alpine meadows. The movement and abundance of the butterfly Parnassius smintheus in the meadows were monitored using mark–release–recapture methods.2. A total of 937 butterflies, 698 males and 239 females, was captured. There were 223 observed between-meadow movements. Fifty-two per cent of males and 35% of females moved among meadows.3. The immigration of male butterflies was related positively to nectar flowers, host plant abundance, and female butterflies. Male emigration was not affected by any of the treatments. The number of males captured was related positively to nectar flowers and host plants but not affected by sex ratio. The number of resident male butterflies was greater in meadows containing flowers and was related positively to host plant abundance, but unaffected by sex ratio.4. Flower removal, sex ratio, and abundance of Sedum had no significant effect on the abundance, movement, or residence time for female butterflies, in part due to small sample size.5. The fact that males immigrate to higher quality meadows suggests that male butterflies are assessing meadow quality, either by sampling meadows or potentially from a distance using olfactory cues.
Ecological Entomology 05/2002; 27(3):308 - 316. · 2.00 Impact Factor
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Hereditas 02/2002; 136(3):247-50. · 0.79 Impact Factor
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ABSTRACT: Butterflies disperse readily through meadow, but forests are twice as resistant to butterfly movement. Butterflies tend to stay in areas with high density but abandon small populations. In this species, movement is mostly along ridge-tops, making this effectively a 1-dimensional universe.
Ecology. 01/2000; 81:1642-1653.
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ABSTRACT: Foraging by migratory pine siskins in an apple orchard infested with varying densities of winter moth was observed, and winter moth mortality in the presence and absence of birds was recorded. Time spent foraging in a tree and number of birds foraging per tree was positively related to larval density but number of larvae removed per leaf cluster or per unit time was not. Level of defoliation was a better predictor of the number of clusters searched per tree than was prey density. Despite poor predictability in allocation of search effort with respect to prey density, siskins acted as a source of strong compensatory mortality on the winter moth population.
Oecologia 03/1986; 69(1):47-52. · 3.41 Impact Factor
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