Roger I. C. Hansell

Establishment of white spruce populations and responses to climatic change at the treeline, Churchill, Manitoba, Canada

Studies on recruitment of white spruce from 1785 to present document the open forest succession at Churchill, Manitoba. Advance of trees onto land emerging from Hudson Bay due to isostatic uplift and permafrost intrusion has resulted in the development of two distinct systems. Open forest and forest-tundra are distinguished by seedling establishment, crown forms, and the growth patterns of the trees. Forest-tundra plots which demonstrate transition to open forest are documented. Where the two systems were established prior to the major climatic warming, they are resistant to invasion and there is little resultant change in the position of the treeline. Once started, population growth within the open forest system tends to be self generating and is little affected by subsequent climatic cooling. The mature open forest established prior to 1800 has shown a decline in seedling establishment during the climatic warming. These sites are characterized by extensive lichen cover.

Drosophila larval foraging behavior. II. Selection in the sibling species,D. melanogaster andD. simulans

A laboratory study is presented which shows that larval foraging behavior in the sibling speciesDrosophila melanogaster andD. simulans can respond rapidly (in six generations) to unidirectional selection. An apparatus was designed which selected for larvae which moved from nonnutritive agar medium to plugs of nutritive medium and remained feeding there. Larvae of the selected lines showed a correlated decrease in foraging path length which mirrored thesitter larval forager behavior type previously defined by Sokolowski [(1980).Behav. Genet.10:291–302]. This supported the hypothesis that sitter larvae moved toward, and remained feeding on, a food source when they were not already utilizing one, whereasrover larvae foraged from food patch to food patch.

CROWN FORMS AND SHOOT ELONGATION OF WHIlE SPRUCE AT IHE TREELINE, CHURCHILL, MANITOBA, CANADA

Five crown forms of treeline white spruce are used to define open forest, forest-tundra, and tundra regions at Churchill, Manitoba, Canada. Shoot elongation of 25-, 50-, and 100-yrold open forest trees was studied on a transect through an area of forest succession during 1983. During 1984, shoot elongation of different crown forms was examined relative to ground temperatures, air temperatures, and precipitation. Stem and branch elongation of open forest trees was greatest and occurred over the longest period of time, followed by forest-tundra trees, and tundra trees. The increasing density of spruce in the zone of invading open forest is associated with moss development that moderates the ground temperature, increasing the lower root zone temperature early in the growing season and maintaining lower temperatures in the upper root zone later in the season. Continued moss accumulation coincides with permafrost formation into the root base. On the foresttundra and tundra, moss development is patchy. Early warming of the peat surface results in drying that impedes heat influx to the lower root zone. The temperatures in the lower root zone appear limiting to forest-tundra trees and restricting to tundra trees at the start of the growing season. Shoot elongation is over before the upper root zone becomes very hot. Treeline crown forms are grouped according to similar patterns of elongation and common types of development. The wind-abraded crown forms are caused by slow growth that leaves a tree exposed to wind effects for a longer period of time.

Elucidating the Behavioral Phenotype of Drosophila melanogaster Larvae: Correlations Between Larval Foraging Strategies and Pupation Height

Larvae which demonstrated long trails covering a large area while feeding (rover foragers) pupated significantly higher than those covering a relatively small area and exhibiting short paths (sitter foragers). Pupation height and density of larvae per vial were positively correlated. Under the condition of equal larval density per vial,rovers were found to pupate significantly higher thansitter larval foragers. The effect of three light regimes (constant light, constant darkness, and 12 h light followed by 12 h dark) indicated a more complex relationship between pupation height and larval foraging behavior.

Large-Scale Changes in Atmospheric Circulation Interpreted From Patterns of Tree Growth at Churchill, Manitoba, Canada

Growth layer analysis involving 11 treeline white spruce (Picea glauca) and two tamarack (Larix laricina) from Churchill, Manitoba, Canada, produced a data set with some 500,000 tree rings. A summary of these data is made using knowledge of tree growth and weather stresses. The growth trends conform well to Northern Hemisphere and Arctic temperature data sets and poorly to local temperatures. The summer position of the Arctic Front is close to the treeline and some periods of tree growth are dominated by arctic conditions while others are dominated by more temperate conditions. The period 1760 to 1820 shows intermittent dominance of temperate conditions while the period 1921 to 1970 shows a complete dominance of temperate conditions. All other years from 1715 to 1982 show a dominance of arctic conditions. Under the cool Arctic air mass the trends longer than 8 yr are suppressed and poorly defined relative to the trends in hemispheric temperature data. The presence of the Arctic Front to the north of Churc...

ATMOSPHERIC CHANGE AND BIODIVERSITY IN THE ARCTIC

The Canadian Arctic is characterized by a high variation in landform types and there are complex interactions between land, water and the atmosphere which dramatically affect the distribution of biota. Biodiversity depends upon the intensity, predictability and scale of these interactions. Observations, as well as predictions of large-scale climate models which include ocean circulation, reveal an anomalous cooling of northeastern Canada in recent decades, in contrast to the overall significant increase in average annual temperature in the Northern Hemisphere. Predictions from models are necessary to forecast the change in the treeline in the 21st century which may lead to a major loss of tundra. The rate of change in vegetation in response to climate change is poorly understood. The treeline in central Canada, for example, is showing infilling with trees, and in some locations, northerly movement of the boundary. The presence of sea ice in Hudson Bay and other coastal areas is a major factor affecting interactions between the marine and terrestrial ecosystems. Loss of ice and therefore hunting of seals by polar bears will reduce bear and arctic fox populations within the region. In turn, this is likely to have significant effects on their herbivorous prey populations and forage plants. Further, the undersurface of sea ice is a major site for the growth of algae and marine invertebrates which in turn act as food for the marine food web. A rise in sea-level may flood coastal saltmarsh communities leading to changes in plant assemblages and a decline in foraging by geese and other consumers. The anomalous cooling in the eastern Arctic, primarily in late winter and early spring, has interrupted northern migration of breeding populations of geese and ducks and led to increased damage to vegetation in southern arctic saltmarshes as a result of foraging. It is likely that there has been a significant loss of invertebrates in those areas where the vegetation has been destroyed. Warming will have major effects on permafrost distribution and on ground-ice resulting in a major destabilization of slopes and slumping of soil, and disruption of tundra plant communities. Disruption of peat and moss surfaces lead to loss of insulation, an increase in active-layer depth and changes in drainage and plant assemblages. Increases of UV-B radiation will strongly affect vulnerable populations of both plants and animals. The indigenous peoples will face major changes in life style, edibility of food and health standards, if there is a significant warming trend. The great need is for information which is sensitive to the changes and will assist in developing an understanding of the complex interactions of the arctic biota, human populations and the physical environment.

Measuring perturbation in a complicated, thermodynamic world

Abstract Our inability to measure perturbation beyond a context- or system-specific manner has been a fundamental bottleneck to the generalisation of a great number of ecological concepts. Here we develop and explore a thermodynamically inspired solution to this problem as developed by Prigogine and colleagues. We empirically and theoretically demonstrate how the ratio of community respiration to community biomass is an index of the distance from a general thermodynamic steady-state. Using this approach, we re-examine some very old ecological questions (e.g. the patterns of size and abundance; the spatio–temporal complexity of ecological interactions) and other more recent questions (e.g. the leakiness/efficiency of food webs; the relevance of non-linear interactions and critical behaviour to ecology). We discuss these implications and connections and develop a strong theoretical and physical foundation for the study of ecological change.

PREDICTING CHANGE IN NON-LINEAR SYSTEMS

Complex systems are characterizedby surprising switches to new behaviours. Evaluating and predicting these changes demands anunderstanding of the behaviour of the whole system. The combined ecosystem-climate system shows chaoticor pseudorandom behaviour, stochastic or trulyrandom behaviour, as well as simple bifurcation andsemi-stability. Semistability involves the suddenchange from a destabilized ’attractor‘ to a newstable attractor which may occur after an apparentlyunpredictable time delay. We present some recentresults for analyzing time series data and for usingsimulations of non-linear models to predict these changes.

Behavioral evolution and biocultural games: oblique and horizontal cultural transmission

We consider an evolutionary game model in which strategies are culturally transmitted among individuals rather than inherited biologically. In addition to vertical transmission (from parents to offspring), we investigate the effects of oblique (from members of the parental generation to offspring) and horizontal (among age peers) transmission on game dynamics. Our study yields two important results. Firstly, biocultural games show a greater diversity of dynamical behaviors than their purely biological counterparts, including multiple fully polymorphic equilibria. Secondly, biocultural games on average show greater equilibrium strategy diversity. These results suggest that cultural transmission in the presence of natural selection may be an important mechanism maintaining behavioral diversity in natural populations.

Drosophila larval foraging behavior. I. The sibling species,D. melanogaster andD. simulans

Phenotypic variation in foraging patterns of laboratory strains ofDrosophila melanogaster andD. simulans is reported in this paper. Mean scores of several replicate samples of each strain are compared to determine if both species show similar amounts of variation in each of the measures of foraging behavior. The mean scores for crawling and shoveling behavior performed by each species were similar. However,D. melanogaster showed greater intrastrain differences in mean crawling and mean shoveling scores than didD. simulans. In contrast,D. simulans showed greater intrastrain differences between the mean path lengths and the average areas traversed than didD. melanogaster.