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Roles and Effects of Environmental Carbon Dioxide in Insect Life
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Key Words
behavior, olfaction, antennal lobe, herbivory, oviposition
Abstract
Carbon dioxide (CO2) is a ubiquitous sensory cue that plays mul- tiple roles in insect behavior. In recent years understanding of the well-known role of CO2 in foraging by hematophagous insects (e.g., mosquitoes) has grown, and research on the roles of CO2 cues in the foraging and oviposition behavior of phytophagous insects and in behavior of social insects has stimulated interest in this area of insect sensory biology. This review considers those advances, as well as some of the mechanistic bases of the modulation of behavior by CO2 and important progress in our understanding of the detection and CNS processing of CO2 information in insects. Finally, this review briefly addresses how the ongoing increase in atmospheric CO2 levels may affect insect life.
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Can Plants Adapt? New Questions in Climate Change Research
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As it becomes increasingly apparent that human activities are partly responsible for global warming, the focus of climate change research is shifting from the churning out of assessments to the pursuit of science that can test the robustness of existing models. The questions now being addressed are becoming more challenging:The questions now being addressed are becoming more challenging: Can water-use efficiency of plants keep up with rising temperatures? Will we see a greening period for some decades, even a century, before facing a rapid browndown as threshold temperatures are reached? Or could the thresholds be reached much sooner because of interactions of biophysical processes? Is the carbon storage issue missing the point?
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Montane meadow change during drought varies with background hydrologic regime and plant functional group
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Key words:drought; forbs; hydrological gradient; plant community; woody plants.
Abstract. Climate change models for many ecosystems predict more extreme climatic events in the future, including exacerbated drought conditions. Here we assess the effects of drought by quantifying temporal variation in community composition of a complex montane meadow landscape characterized by a hydrological gradient. The meadows occur in two regions of the Greater Yellowstone Ecosystem (Gallatin and Teton) and were classified into six categories (M1–M6, designating hydric to xeric) based upon Satellite pour l’Observation de la Terre (SPOT) satellite imagery. Both regions have similar plant communities, but patch sizes of meadows are much smaller in the Gallatin region. We measured changes in the percent cover of bare ground and plants by species and functional groups during five years between 1997 and 2007. We hypothesized that drought effects would not be manifested evenly across the hydrological gradient, but rather would be observed as hotspots of change in some areas and minimally evident in others. We also expected varying responses by plant functional groups (forbs vs. woody plants). Forbs, which typically use water from relatively shallow soils compared to woody plants, were expected to decrease in cover in mesic meadows, but increase in hydric meadows. Woody plants, such as Artemisia, were expected to increase, especially in mesic meadows. We identified several important trends in our meadow plant communities during this period of drought: (1) bare ground increased significantly in xeric meadows of both regions (Gallatin M6 and Teton M5) and in mesic (M3) meadows of the Teton, (2) forbs decreased significantly in the mesic and xeric meadows in both regions, (3) forbs increased in hydric (M1) meadows of the Gallatin region, and (4) woody species showed increases in M2 and M5 meadows of the Teton region and in M3 meadows of the Gallatin region. The woody response was dominated by changes in Artemisia spp. and Chrysothamnus viscidiflorus. Thus, our results supported our expectations that community change was not uniform across the landscape, but instead could be predicted based upon functional group responses to the spatial and temporal patterns of water availability, which are largely a function of plant water use and the hydrological gradient.
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A Large-Scale Deforestation Experiment: Effects of Patch Area and Isolation on Amazon Birds
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As compared with extensive contiguous areas, small isolated habitat patches lack many species. Some species disappear after isolation; others are rarely found in any small patch, regardless of isolation. We used a 13-year data set of bird captures from a large landscape-manipulation experiment in a Brazilian Amazon forest to model the extinction-colonization dynamics of 55 species and tested basic predictions of island biogeography and metapopulation theory. From our models, we derived two metrics of species vulnerability to changes in isolation and patch area. We found a strong effect of area and a variable effect of isolation on the predicted patch occupancy by birds.
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From Individual Dispersal to Species Ranges: Perspectives for a Changing World
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Dispersal is often risky to the individual, yet the long-term survival of populations depends on having a sufficient number of individuals that move, find each other, and locate suitable breeding habitats. This tension has consequences that rarely meet our conservation or management goals. This is particularly true in changing environments, which makes the study of dispersal urgently topical in a world plagued with habitat loss, climate change, and species introductions. Despite the difficulty of tracking mobile individuals over potentially vast ranges, recent research has revealed a multitude of ways in which dispersal evolution can either constrain, or accelerate, species’ responses to environmental changes.
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How Does It Feel to Be Like a Rolling Stone? Ten Questions About Dispersal Evolution
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This review proposes ten tentative answers to frequently asked ques- tions about dispersal evolution. I examine methodological issues, model assumptions and predictions, and their relation to empirical data. Study of dispersal evolution points to the many ecological and genetic feedbacks affecting the evolution of this complex trait, which has contributed to our better understanding of life-history evolution in spatially structured populations. Several lines of research are suggested to ameliorate the exchanges between theoretical and empirical studies of dispersal evolution.
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The effect of changing climate on the frequency of absolute extreme events
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n some areas of climate impact analysis, the possible impact of a changing mean
climate has been dismissed by some writers either because of a belief that society can adapt to a slowly changing mean and/or because expected rates of future changes lie within or not far outside those experienced in the past. The two standard counter arguments to this optimistic view are: (1) the future will lead to much longer periods of protracted change in one direction, with final conditions well into the no-analogue region; and/or (2) the main impacts will accrue through changes in the frequency of extremes. In the literature on greenhouse effect, lip service is often paid to the effect of changes in the frequency of extremes. But just how will a slowly changing mean affect the frequency of extremes?
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Vegetation Responses to Extreme Hydrological Events: Sequence Matters
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Extreme hydrological events such as flood and drought drive vegetation dynamics and are projected to increase in frequency in association with climate change, which could result in sequences of extreme events. However, experimental studies of vegetation re- sponses to climate have largely focused on responses to a trend in climate or to a single extreme event but have largely overlooked the potential for complex responses to specific sequences of extreme events. Here we document, on the basis of an experiment with seed- lings of three types of subtropical wetland tree species, that mortality can be amplified and growth can even be stimulated, depending on event sequence. Our findings indicate that the impacts of multiple extreme events cannot be modeled by simply summing the projected effects of individual extreme events but, rather, that models should take into account event sequences.
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Climatic extremes improve predictions of spatial patterns of tree species
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Understanding niche evolution, dynamics, and the response of species to climate change requires knowledge of the determinants of the environmental niche and species range limits. Mean values of climatic variables are often used in such analyses. In contrast, the increasing frequency of climate extremes suggests the importance of understanding their additional influence on range limits. Here, we assess how measures representing climate extremes (i.e., interannual variability in climate parameters) explain and predict spatial patterns of 11 tree species in Switzerland. We find clear, although comparably small, improvement (20% in adjusted D2, 8% and 3% in cross-validated True Skill Statistic and area under the receiver operating characteristics curve values) in models that use measures of extremes in addition to means. The primary effect of including information on climate extremes is a correction of local overprediction and underprediction. Our results demonstrate that measures of climate extremes are important for understanding the climatic limits of tree species and assessing species niche characteristics. The inclusion of climate variability likely will improve models of species range limits under future conditions, where changes in mean climate and increased variability are expected.
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Tree spatial patterns in fire-frequent forests of western North America, including mechanisms of pattern formation and implications for designing fuel reduction and restoration treatments
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Restoring characteristic fire regimes and forest structures are central objectives of many restoration and fuel reduction projects. Within-stand spatial pattern is a fundamental attribute of forest structure and influences many ecological processes and ecosystem functions. In this review we synthesize the available spatial reference information for fire-frequent pine and mixed-conifer forests in western North America; interpret this information in the context of restoration and fuel reduction treatment design; and identify areas for future research, including recommended approaches for quantifying within-stand tree spatial patterns.
We identified 50 studies of tree spatial patterns in fire-frequent pine and mixed conifer forests, 25 of which documented spatial reference conditions. The characteristic structure of fire-frequent forests is a mosaic of three elements: openings, single trees, and clumps of trees with adjacent or interlocking crowns. This mosaic structure typically manifests at scales <0.4 ha, but sometimes extends to scales as large as 4 ha, particularly on sites with fire regimes that include both low- and moderate-severity fires. We documented preferential use of global pattern analysis techniques (90% of analyses) relative to local analysis techniques (10% of analyses). Ripley’s K statistic, an example of global spatial pattern analysis, was the most frequently used analytic technique (38% of analyses). These findings are important because global pattern analysis does not explicitly quantify spatial heterogeneity within a pattern, the very thing spatial reference studies seek to characterize and one of the core structural attributes treatments aim to restore.
Based on these findings, we encourage managers to consciously adopt a view of forest structure that accommodates spatial heterogeneity within forest stands, and to use this conceptualization of forest structure to guide prescription development. Restoration prescriptions and marking guidelines that explicitly incorporate within-stand spatial heterogeneity—such as by specifying the numbers and sizes of openings and tree clumps, and the number of widely-spaced single trees to retain per unit area—will improve the likelihood of restoring characteristic forest structures and the ecological processes such structures support. We infer that the near-exclusive use of global pattern analysis has limited the quan- tity and usability of spatial reference information available to managers, has also likely limited the development and testing of novel ecological hypotheses about pattern-generating mechanisms. Consequently, we recommend that forest scientists change how they quantify tree spatial patterns by complimenting the traditional global analysis methods with local pattern analysis techniques, which quantify spatial heterogeneity within a study area.
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