Response of a Reptile Guild to Forest Harvesting

Abstract:  Despite the growing concern over reptile population declines, the effects of modern industrial silviculture on reptiles have been understudied, particularly for diminutive and often overlooked species such as small-bodied snakes. We created 4 replicated forest-management landscapes to determine the response of small snakes to forest harvesting in the Coastal Plain of the southeastern United States. We divided the replicated landscapes into 4 treatments that represented a range of disturbed habitats: clearcut with coarse woody debris removed; clearcut with coarse woody debris retained; thinned pine stand; and control (unharvested second-growth planted pines). Canopy cover and ground litter were significantly reduced in clearcuts, intermediate in thinned forests, and highest in unharvested controls. Bare soil, maximum air temperatures, and understory vegetation all increased with increasing habitat disturbance. Concomitantly, we observed significantly reduced relative abundance of all 6 study species (scarletsnake [Cemophora coccinea] , ring-neck snake [Diadophis punctatus] , scarlet kingsnake [Lampropeltis triangulum] , red-bellied snake [Storeria occipitomaculata] , southeastern crowned snake [Tantilla coronata] , and smooth earthsnake [Virginia valeriae] ) in clearcuts compared with unharvested or thinned pine stands. In contrast, the greatest relative snake abundance occurred in thinned forest stands. Our results demonstrate that at least one form of forest harvesting is compatible with maintaining snake populations. Our results also highlight the importance of open-canopy structure and ground litter to small snakes in southeastern forests and the negative consequences of forest clearcutting for small snakes.     

Simulation and analysis of outbreaks of bark beetle infestations and their management at the stand level

Outbreaks of bark beetles in forests can result in substantial economic losses. Understanding the factors that influence the development and spread of bark beetle outbreaks is crucial for forest management and for predicting outbreak risks, especially with the expected global warming. Although much research has been done on the ecology and phenology of bark beetles, the complex interplay between beetles, host trees, beetle antagonists and forest management makes predicting beetle population development especially difficult. Using the recent infestations of the European Spruce Bark Beetle (Ips typographus L. Col. Scol.) in the Bavarian Forest National Park (Germany) as a case study, we developed a spatially explicit agent-based simulation model (SAMBIA) that takes into account individual trees and beetles. This model primarily provides a tool for analysing and understanding the spatial and temporal aspects of bark beetles outbreaks at the stand scale. Furthermore, the model should allow an estimation of the effectiveness of concurrent impacts of both antagonists and management to confine outbreak dynamics in practice. We also used the model to predict outbreak probabilities in various settings. The simulation results indicated a distinct threshold behaviour of the system in response to pressure by antagonists or management of the bark beetle population. Despite the different scenarios considered, we were able to extract from the simulations a simple rule of thumb for the successful control of an outbreak: if roughly 80% of individual beetles are killed by antagonists or foresters, outbreaks will rarely take place. Our model allows the core dynamics of this complex system to be reduced to this inherent common denominator.     

Mixed messages across multiple trophic levels: the ecology of bark beetle chemical communication systems

Summary. Chemical, physiological and behavioral components of pheromone communication have been described for a number of bark beetle species, yet our understanding of how these signals function under natural conditions remains relatively limited. Development of ecologically based models is complicated by the multiple functions and sources of variability inherent in bark beetle semiochemistry. This discussion addresses four ecological issues of chemical signaling in bark beetles: the effects of aggregation on individual fitness, the possibility of cheating, how plants can defend themselves against herbivores that employ aggregation pheromones, and the implications of variability in chemical communication systems to predator avoidance. An analysis of published data from thirteen scolytid – conifer systems indicates that the net benefit and optimal colonization density vary with host condition and beetle species. When beetles attack live trees, the benefit of cooperative host procurement exceeds losses due to competition for the limited substrate, at least up to moderate densities. When beetles colonize dead tissue, however, the effect of subsequently arriving beetles on initial colonizers is almost entirely negative. This suggests that aggregation originated as exploitation of senders, but evolved into manipulation of receivers. It is also proposed that the optimal colonization density which typifies each species or population may offer a more objective and less value–laden index of behavior than current labels such as “aggressiveness”. Beetles can maximize the relative benefits of group attack by incorporating instantaneous measures of host resistance into their colonization behavior, and by adjusting oviposition with colonization density. This system may provide opportunities for cheating. However a number of factors may select against a fixed strategy of cheating, including the linkage between tree allelochemistry and beetle semiochemistry, the reduced quality of substrate available to late arrivers, the short adult lifespans of most bark beetles, differential exposure to some predators, the difficulty of locating signalers during extensive endemic periods, and the low costs incurred during host assessment. However, the possibility that beetles employ flexible, density – dependent strategies deserves heightened attention. The ability of bark beetles to collectively exhaust host defenses poses a particular problem for plant defense. It is argued here that the ideal defense should include both direct resistance mechanisms against invading beetles, and indirect mechanisms that inhibit chemical communication. Evidence for the latter mechanism is explored. The ability of predators to efficiently exploit aggregation pheromones as kairomones in prey finding poses significant risk to bark beetles. It is proposed that minor alterations in pheromone components may provide colonizers with partial escape from such natural enemies while maintaining intraspecific functionality. Traditional interpretations emphasized the fidelity and consistency of pheromones, but under natural conditions chemical signals are modified by unpredictable features of the biotic and abiotic environment. Although we typically view variation in pheromonal signals as experimental noise or simple deviations from a population norm, such variation may reflect evolutionary dynamics. Complex ecological interactions may impose trade-offs between the clarity versus diversity of their signals. Received 3 July 2000; accepted 8 January 2001     

Irruptive population dynamics in Yellowstone pronghorn.

Irruptive population dynamics appear to be widespread in large herbivore populations, but there are few empirical examples from long time series with small measurement error and minimal harvests. We analyzed an 89-year time series of counts and known removals for pronghorn (Antilocapra americana) in Yellowstone National Park of the western United States during 1918-2006 using a suite of density-dependent, density-independent, and irruptive models to determine if the population exhibited irruptive dynamics. Information-theoretic model comparison techniques strongly supported irruptive population dynamics (Leopold model) and density dependence during 1918-1946, with the growth rate slowing after counts exceeded 600 animals. Concerns about sagebrush (Artemisia spp.) degradation led to removals of >1100 pronghorn during 1947-1966, and counts decreased from approximately 700 to 150. The best models for this period (Gompertz, Ricker) suggested that culls replaced intrinsic density-dependent mechanisms. Contrary to expectations, the population did not exhibit enhanced demographic vigor soon after the termination of the harvest program, with counts remaining between 100 and 190 animals during 1967 1981. However, the population irrupted (Caughley model with a one-year lag) to a peak abundance of approximately 600 pronghorn during 1982-1991, with a slowing in growth rate as counts exceeded 500. Numbers crashed to 235 pronghorn during 1992-1995, perhaps because important food resources (e.g., sagebrush) on the winter range were severely diminished by high densities of browsing elk, mule deer, and pronghorn. Pronghorn numbers remained relatively constant during 1996-2006, at a level (196-235) lower than peak abundance, but higher than numbers following the release from culling. The dynamics of this population supported the paradigm that irruption is a fundamental pattern of growth in many populations of large herbivores with high fecundity and delayed density-dependent effects on recruitment when forage and weather conditions become favorable after range expansion or release from harvesting. Incorporating known removals into population models that can describe a wide range of dynamics can greatly improve our interpretation of observed dynamics in intensively managed populations.     

Population feedback after successful invasion leads to ecological suicide in seasonal environments

For most consumer species, winter represents a period of harsh food conditions in addition to the physiological strain that results from the low ambient temperatures. In size-structured populations, larger-bodied individuals do better during winter as they have larger energy reserves to buffer starvation periods. In contrast, smaller-bodied individuals do better under growing conditions, as they have lower maintenance costs. We study how the interplay between size-dependent life-history processes and seasonal changes in temperature and food availability shape the long-term dynamics of a size-structured consumer population and its unstructured resource. We show that the size dependence of maintenance requirements translates into a minimum body size that is needed for surviving starvation when consumers can adapt only to a limited extent to the low food densities in winter. This size threshold can lead to population extinction because adult individuals suffer only a little during winter and hence produce large numbers of offspring. Due to population feedback on the resource and intense intra-cohort competition, newborn consumers then fail to reach the size threshold for survival. Under these conditions, small numbers of individuals can survive, increase in density, and build up a population, which will subsequently go extinct due to its feedback on the resource. High juvenile mortality may prevent this ecological suicide from occurring, as it releases resource competition among newborns and speeds up their growth. In size-structured populations, annual fluctuations in temperature and food availability may thus lead to a conflict between individual fitness and population persistence.     

The influences of climate and hydrology on population dynamics of waterbirds in the lower Murrumbidgee River floodplains in Southeast Australia: Implications for environmental water management

Restoration of waterbird diversity and abundance is a key objective of river system management in Australia. Therefore, understanding the effects of climatic and hydrological variables on waterbird population dynamics is fundamental for successful river restoration programs. We investigated the population dynamics of waterbirds (total abundance) and seven functional waterbird groups in the floodplains of lower Murrumbidgee River. We found a general declining abundance trend from 1983 to 2007, except for the deep water foragers. We modelled the relative contribution of the climatic and hydrological factors to waterbird population decrease using the generalized additive model (GAM) framework after identifying the negative binomial distribution. Most of the seven functional groups were positively related to both annual rainfall and water usage, defined as the total water volume intercepted by the river reach, and the models indicated that rainfall was slightly more important. Temperature also played a role in waterbird abundance: the maximum summer temperature negatively influenced the abundance of dabbling ducks, shoreline foragers and fish eaters, while the minimum winter temperature positively affected the abundance of dabbling ducks and shoreline foragers. Overall, our results support the practice of providing environmental water for sustaining waterbird populations. However, environmental water provision is likely to be most effective when timed to coincide with antecedent rainfall.     

Prehistoric Decline in Freshwater Mussels Coincident with the Advent of Maize Agriculture

Abstract:  During late prehistory, high population densities and intensive agricultural practices of Native American societies had profound effects on the pre-Columbian landscape. The degree to which Native American land use affected aquatic ecosystems is unknown. Freshwater mussels are particularly sensitive harbingers of modern-day ecosystem deterioration. We used data from prehistoric Native American shell middens to examine prehistoric trends in abundance of freshwater mussels of the genus Epioblasma in North America during the last 5000 years. The relative abundance of Epioblasma declined steadily during this period, a result that could be explained either by an increase in human impacts to streams or by long-term climatic changes unrelated to human activities. The rate of decline of Epioblasma increased significantly, however, after the advent of large-scale maize agriculture in the southeastern United States about 1000 years before the present. Our results suggest that human land-use activities in prehistory caused changes in freshwater mussel communities that were lower in magnitude but similar in direction to changes caused by recent activities.     

Can ocean acidification affect population dynamics of the barnacle Semibalanus balanoides at its southern range edge?

The global ocean and atmosphere are warming. There is increasing evidence suggesting that, in addition to other environmental factors, climate change is affecting species distributions and local population dynamics. Additionally, as a consequence of the growing levels of atmospheric carbon dioxide (CO2), the oceans are taking up increasing amounts of this CO2, causing ocean pH to decrease (ocean acidification). The relative impacts of ocean acidification on population dynamics have yet to be investigated, despite many studies indicating that there will be at least a sublethal impact on many marine organisms, particularly key calcifying organisms. Using empirical data, we forced a barnacle (Semibalanus balanoides) population model to investigate the relative influence of sea surface temperature (SST) and ocean acidification on a population nearing the southern limit of its geographic distribution. Hindcast models were compared to observational data from Cellar Beach (southwestern United Kingdom). Results indicate that a declining pH trend (-0.0017 unit/yr), indicative of ocean acidification over the past 50 years, does not cause an observable impact on the population abundance relative to changes caused by fluctuations in temperature. Below the critical temperature (here T(crit) = 13.1 degrees C), pH has a more significant affect on population dynamics at this southern range edge. However, above this value, SST has the overriding influence. At lower SST, a decrease in pH (according to the National Bureau of Standards, pHNBs) from 8.2 to 7.8 can significantly decrease the population abundance. The lethal impacts of ocean acidification observed in experiments on early life stages reduce cumulative survival by approximately 25%, which again will significantly alter the population level at this southern limit. Furthermore, forecast predictions from this model suggest that combined acidification and warming cause this local population to die out 10 years earlier than would occur if there was only global warming and no concomitant decrease in pH.     

A resource-depletion model of forest insect outbreaks

Detailed analyses of thresholded ecological interactions can improve our understanding of the transition from aperiodic to periodic dynamics. We develop a threshold model of the population dynamics of outbreaking bark beetle populations that alternate between non-epidemic and epidemic behavior. The model involves accumulation of resources during low-density periods and depletion during outbreaks. The transition between the two regimes is caused by disturbance events in the form of major tree felling by wind. The model is analyzed with particular reference to the population dynamics of the spruce bark beetle (Ips typographus) in Scandinavia for which a comprehensive literature allows full parameterization. The fairly constant outbreak lengths and the highly variable waiting time between outbreaks that are seen in the historical records of this species agree well with the predictions of the model. The thresholded resource-depletion dynamics result in substantial variation in the degree of periodicity between stochastic realizations. The completely aperiodic tree colonizations are partly predictable when the timing of the irregular windfall events are known. However, the predictability of inter-outbreak periods is low due to the large variation of cases falling most frequently in the middle between the extremes of purely nonperiodic (erratic) and periodic (cyclic) fluctuations.     

The Importance of the Water Conservation Areas in the Everglades to the Endangered Wood Stork (Mycteria americana)

During 1985–1989, numbers of the endangered Wood Stork ( Mycteria americana ) in the Water Conservation Areas of the Everglades, Florida, showed an annual peak in February or March of 1233 to 7874 birds. The annual maxima are significantly greater in dry years than in wet years (P < 0.05). Most storks are nonbreeders and are found foraging in open habitats along the eastern and southern parts of Conservation Area 1 and Conservation Area 2A and along the west-central side of Conservation Area 3A. In dry years, large numbers move into the southern half of Conservation Area 3A. We estimated that in spring, the total southeastern United States population of Wood Storks is between 14,000 and 20,000 individuals. The annual maxima of the water conservation areas were at least 8% to 10% of the total southeastern U.S. population in wet years and possibly as much as 55% in dry years. The Water Conservation Areas appear to be critical foraging habitat for wintering storks, especially during drought years when most of the rest of south Florida is dry. Changes in the management of these areas could have a major impact on the status of storks throughout the southeastern United States.     

Do novel genotypes drive the success of an invasive bark beetle-fungus complex? Implications for potential reinvasion

Novel genotypes often arise during biological invasions, but their role in invasion success has rarely been elucidated. Here we examined the population genetics and behavior of the fungus, Leptographium procerum, vectored by a highly invasive bark beetle, Dendroctonus valens, to determine whether genetic changes in the fungus contributed to the invasive success of the beetle-fungal complex in China. The fungus was introduced by the beetle from the United States to China, where we identified several novel genotypes using microsatellite markers. These novel genotypes were more pathogenic to Chinese host seedlings than were other genotypes and they also induced the release of higher amounts of 3-carene, the primary host attractant for the beetle vector, from inoculated seedlings. This evidence suggests a possible mechanism, based on the evolution of a novel genotype during the two or three decades since its introduction, for the success of the beetle-fungal complex in its introduced region.     

Temperature as a key driver of ecological sorting among invasive pest species in the tropical Andes

Invasive species are a major threat to the sustainable provision of ecosystem products and services, both in natural and agricultural ecosystems. To understand the spatial arrangement of species successively introduced into the same ecosystem, we examined the tolerance to temperature and analyzed the field distribution of three potato tuber moths (PTM, Lepidoptera: Gelechiidae), that were introduced in Ecuador since the 1980s. We studied physiological responses to constant temperatures of the three PTM species under laboratory conditions and modeled consequences for their overall population dynamics. We then compared our predictions to field abundances of PTM adults collected in 42 sites throughout central Ecuador. Results showed that the three PTM species differed with respect to their physiological response to temperature. Symmetrischema tangolias was more cold tolerant while Tecia solanivora had the highest growth rates at warmer temperatures. Phthorimaea operculella showed the poorest physiological performance across the range of tested temperatures. Overall, field distributions agree with predictions based on physiological experiments and life table analyses. At elevations >3000 m, the most cold-tolerant species, S. tangolias, was typically dominant and often the only species present. This species may therefore represent a biological sensor of climate change. At low elevations (<2700 m), T. solanivora was generally the most abundant species, probably due to its high fecundity at high temperatures. At mid elevations, the three species co-occurred, but P. operculella was generally the least abundant species. Consistent with these qualitative results, significant regression analyses found that the best predictors of field abundance were temperature and a species x temperature interaction term. Our results suggest that the climatic diversity in agricultural landscapes can directly affect the community composition following sequential invasions. In the tropical Andes, as in other mountain ecosystems, the wide range of thermal environments found along elevational gradients may be one reason why the risks of invasion by successively introduced pest species could increase in the near future. More data on potential biological risks associated with climatic warming trends in mountain systems are therefore urgently needed, especially in developing nations where such studies are lacking.     

Recolonizing wolves and mesopredator suppression of coyotes: impacts on pronghorn population dynamics.

Food web theory predicts that the loss of large carnivores may contribute to elevated predation rates and, hence, declining prey populations, through the process of mesopredator release. However, opportunities to test predictions of the mesopredator release hypothesis are rare, and the extent to which changes in predation rates influence prey population dynamics may not be clear due to a lack of demographic information on the prey population of interest. We utilized spatial and seasonal heterogeneity in wolf distribution and abundance to evaluate whether mesopredator release of coyotes (Canis latrans), resulting from the extirpation of wolves (Canis lupus) throughout much of the United States, contributes to high rates of neonatal mortality in ungulates. To test this hypothesis, we contrasted causes of mortality and survival rates of pronghorn (Antilocapra americana) neonates captured at wolf-free and wolf-abundant sites in western Wyoming, USA, between 2002 and 2004. We then used these data to parameterize stochastic population models to heuristically assess the impact of wolves on pronghorn population dynamics due to changes in neonatal survival. Coyote predation was the primary cause of mortality at all sites, but mortality due to coyotes was 34% lower in areas utilized by wolves (P < 0.001). Based on simulation modeling, the realized population growth rate was 0.92 based on fawn survival in the absence of wolves, and 1.06 at sites utilized by wolves. Thus, wolf restoration is predicted to shift the trajectory of the pronghorn population from a declining to an increasing trend. Our results suggest that reintroductions of large carnivores may influence biodiversity through effects on prey populations mediated by mesopredator suppression. In addition, our approach, which combines empirical data on the population of interest with information from other data sources, demonstrates the utility of using simulation modeling to more fully evaluate ecological theories by moving beyond estimating changes in vital rates to analyses of population-level impacts.     

An individual based model of bearded pig abundance

We develop an individual based model of bearded pig abundance which predicts population dynamics based on the processes of energy accumulation and expenditure, reproduction and mortality of individual pigs. Because fatness is a key indicator of condition and reproductive potential in bearded pigs, processes are represented in terms of a fatness index variable. Only a small number of parameters are used in this simple model; these were chosen on the basis of fatness index data and qualitative observations of bearded pig population dynamics. The model was found to be accurate in predicting the timing of observed pig eruptions, and robust in that model results were unaffected by moderate variation in parameter values. There was insufficient quantitative data to obtain precise predictions of fatness and abundance, but qualitative insights about the effects of the size and timing of fruiting events on pig abundance were obtained. The results showed that a single fruiting peak will not produce a bearded pig eruption, no matter how large the fruiting event is, because the duration of the fruiting is too short to allow exponential growth of the population. Consecutive masting events are necessary for an eruption, because if events are separated by more than 1 year, the population will decline to its minimum fatness and abundance levels. It is also necessary for at least one of the fruiting events in a consecutive sequence to be a large event, as consecutive small fruiting events do not increase the fatness enough to cause an eruption. These insights help to explain and predict the effects of changes in mast fruiting patterns on bearded pig populations, such as the predicted increase in frequency and reduction in size of masting fruiting events as a result of climate change.     

Effects of Forest Fragmentation on a Dung Beetle Community in French Guiana

Abstract:  Fragmentation is the most common disturbance induced by humans in tropical forests. Some insect groups are particularly suitable for studying the effects of fragmentation on animal communities because they are taxonomically and ecologically homogenous. We investigated the effects of forest fragmentation on a dung beetle species community in the forest archipelago created in 1994–1995 by the dam of Petit Saut, French Guiana. We set and baited an equal number of pitfall traps for dung beetles on three mainland sites and seven island sites. The sites ranged from 1.1 to 38 ha. In 250 trap days, we captured 50 species in 19 genera. Diversity indices were high (2.18–4.06). The lowest diversity was on the small islands and one mainland site. Species richness and abundance were positively related to fragment area but not to distance from mainland or distance to the larger island. The islands had lower species richness and population than mainland forest, but rarefied species richness was relatively invariant across sites. There was a marked change in species composition with decreasing fragment that was not caused by the presence of a common fauna of disturbed-area species on islands. Small islands differed from larger islands, which did not differ significantly from mainland sites. Partial correlation analyses suggested that species richness and abundance of dung beetle species were positively related to the number of species of nonflying mammals and the density index of howler monkeys ( Alouatta seniculus ), two parameters positively related to fragment area.     

Mapping shifts in spatial synchrony in grassland birds to inform conservation planning

Spatial synchrony, defined as the correlated fluctuations in abundance of spatially separated populations, can be caused by regional fluctuations in natural and anthropogenic environmental population drivers. Investigations into the geography of synchrony can provide useful insight to inform conservation planning efforts by revealing regions of common population drivers and metapopulation extinction vulnerability. We examined the geography of spatial synchrony and decadal changes in these patterns for grassland birds in the United States and Canada, which are experiencing widespread and persistent population declines. We used Bayesian hierarchical models and over 50 years of abundance data from the North American Breeding Bird Survey to generate population indices within a 2° latitude by 2° longitude grid. We computed and mapped mean local spatial synchrony for each cell (mean detrended correlation of the index among neighboring cells), along with associated uncertainty, for 19 species in 2, 26-year periods, 1968–1993 and 1994–2019. Grassland birds were predicted to increase in spatial synchrony where agricultural intensification, climate change, or interactions between the 2 increased. We found no evidence of an overall increase in synchrony among grassland bird species. However, based on the geography of these changes, there was considerable spatial heterogeneity within species. Averaging across species, we identified clusters of increasing spatial synchrony in the Prairie Pothole and Shortgrass Prairie regions and a region of decreasing spatial synchrony in the eastern United States. Our approach has the potential to inform continental-scale conservation planning by adding an additional layer of relevant information to species status assessments and spatial prioritization of policy and management actions. Our work adds to a growing literature suggesting that global change may result in shifting patterns of spatial synchrony in population dynamics across taxa with broad implications for biodiversity conservation.     

Long-term reactions of plants and macroinvertebrates to extreme floods in floodplain grasslands

Extreme summertime flood events are expected to become more frequent in European rivers due to climate change. In temperate areas, where winter floods are common, extreme floods occurring in summer, a period of high physiological activity, may seriously impact floodplain ecosystems. Here we report on the effects of the 2002 extreme summer flood on flora and fauna of the riverine grasslands of the Middle Elbe (Germany), comparing pre- and post-flooding data collected by identical methods. Plants, mollusks, and carabid beetles differed considerably in their response in terms of abundance and diversity. Plants and mollusks, displaying morphological and behavioral adaptations to flooding, showed higher survival rates than the carabid beetles, the adaptation strategies of which were mainly linked to life history. Our results illustrate the complexity of responses of floodplain organisms to extreme flood events. They demonstrate that the efficiency of resistance and resilience strategies is widely dependent on the mode of adaptation.     

A dynamic host selection model for mountain pine beetle,Dendroctonus ponderosae Hopkins

The link between individual habitat selection decisions (i.e., mechanism) and the resulting population distributions of dispersing organisms (i.e., outcome) has been little-studied in behavioural ecology. Here we consider density-dependent habitat (i.e., host) selection for an energy- and time-limited forager: the mountain pine beetle (Dendroctonus ponderosae Hopkins). We present a dynamic state variable model of individual beetle host selection behaviour, based on an individual’s energy state. Field data are incorporated into model parameterization which allows us to determine the effects of host availability (with respect to host size, quality, and vigour) on individuals’ decisions. Beetles choose larger trees with thicker phloem across a larger proportion of the state-space than smaller trees with thinner phloem, but accept lower quality trees more readily at low energy- and time-states. In addition, beetles make habitat selection decisions based on host availability, conspecific attack densities, and beetle distributions within a forest stand. This model provides a framework for the development of a spatial game model to examine the implications of these results for attack dynamics of beetle populations.     

Do birds and beetles show similar responses to urbanization?

To date, the vast majority of studies in urban areas have been carried out on birds, yet it is not known whether the responses of birds to urbanization are congruent with those of other taxa. In this paper, we compared the responses of breeding birds and carabid beetles to urbanization, specifically asking whether the emerging generalizations of the effects of extreme levels of urbanization on birds (declines in total species richness and the richness of specialist species, increases in total abundance and the abundances of native generalist and introduced species, and community simplification, including increasing similarity) could also be applied to ground beetles. We also directly tested for congruence between birds and ground beetles using correlations between variables describing bird and beetle community structure and correlations between bird and beetle distance matrices describing community dissimilarity between pairs of sampling locations. Breeding bird and carabid beetle community data were collected in Ottawa, Ontario, and Gatineau, Quebec, Canada, in two groups of sites: developed sites representing the predictor variable within-site housing density, and forested sites adjacent to development representing the predictor variable neighboring housing density (each site was 0.25 km2). Breeding birds and carabid beetles do not respond similarly to increasing within-site housing density but do exhibit some similar responses to increasing neighboring housing density. Birds displayed strong declines in diversity, compositional changes, and community simplification in response to increasing within-site housing density. Forest and introduced species of birds and beetles responded similarly to increasing housing density within a site, but responses of overall diversity and open-habitat species richness and patterns of community simplification differed between birds and beetles. Increasing neighboring housing density resulted in increases in the abundances of introduced birds and introduced beetles and similar patterns of community simplification in both taxa. To better understand and mitigate the effects of urbanization on biodiversity, we suggest that, in addition to the responses of birds, future research should focus on the responses of other taxa in the urban matrix.     

Quantitative analysis of pyrrolizidine alkaloids sequestered from diverse host plants in Longitarsus flea beetles (Coleoptera, Chrysomelidae)

Summary. Several species of the flea beetles genus Longitarsus are able to sequester pyrrolizidine alkaloids (PAs) from their host plants. In five Longitarsus species we compare the concentration of PAs present in their host plants belonging to the Asteraceae or Boraginaceae with those found in the beetles. To get an estimate of the intrapopulation variability, three samples of five beetles each and five individual plants were analyzed for each comparison. A strong intrapopulation variability could be detected both among plant and beetle samples. The total concentration found in the beetles varied strongly between species. The local host plant and its phenology influence the concentrations present in the beetles as evidenced in comparisons of a single beetle species from two different hosts and of one beetle species collected at the same site at different times of the year. In addition, different beetle species apparently vary in their capacity to sequester the alkaloids, at the lowest extreme the mean PA concentration in the beetles (0.034 μg PA/mg dry weight) was 1/30 of the mean concentration found in the plant leaves (L. aeruginosus from Eupatorium cannabinum), at the highest extreme (2.098 μg PA/mg dw) the concentration in the beetles was a 1000 fold higher than in the plant leaves (L. nasturtii from Symphytum officinale). The highest mean concentration found in the beetles was 3.446 μg/mg dw (L. exoletus from Cynoglossum officinale). The absolute concentrations found in the beetles are comparable to other insects which have been shown to be effectively defended against their potential predators. Received 22 June 1999; accepted 25 August 1999