Responses to Herbivory
Most members of this group are interested
in understanding how plants respond to being eaten.
demonstrated that these responses can be explained in terms of interacting
processes at the individual plant and leaf levels. Increases in photosynthesis
and shifts in C and N allocation contribute to the ability of plants to
tolerate herbivory. Grazing by native herbivores can have positive
effects on subsequent nutrient availability, but the response is contingent
on environmental conditions such as flooding, fire, and temperature (Hik
Merrill and Dale are actively researching how the effects
of herbivory on individual plants may result in patterns at the landscape
level. For example, Dale has found snowshoe hare browsing to have
dramatic effects on the spatial distribution of regenerating white spruce
in the boreal forest, with significant implications for the basic functioning
of these systems and their management.
Historically, studies of herbivory
have focused primarily on interactions above ground. The effects
of belowground feeding on community structure is practically unknown, and
is an active line of research of Cahill and Merrill. Cahill is using
a “root periscope” to determine when roots are eaten, and whether changes
in root structure influence the probability of attack. This technology
is also being used by Cahill to determine how grazing alters root age/size
structure, and the effects these changes on plant function. The ultimate
goal of this project is to determine whether aboveground management decisions
can be modified to maximize rangeland drought resistance.
Hik and Merrill are part of a collaborative effort to develop a state-of-the-art
multi-trophic study center at the Kinsella Research Ranch of the University
of Alberta. Their objectives are to determine the effects of grazing
on grasslands, depending on whether these effects are viewed from the perspective
of plant diversity, primary production, nutrient cycling or consumer population
dynamics. This diversity of views emphasizes the necessity of approaching
questions about the role of herbivory from different levels of biological
organization, a strength within this group.
Considerable effort in
the group is also focused on understanding how the simple act of visiting
plants during field studies influences the intensity of herbivory (Cahill,
Hik, Constabel). Cahill has demonstrated that the effects of researchers
in communities are significant, potentially influencing plant apparancy,
chemistry, and allometry.
This work is also tied to research projects
of Roland and Spence, who focus on understanding the interactions among
plants, herbivores, and parasitoids. Plant cues which parasitoids
use to locate their herbivore hosts have significant implications for both
the general understanding of the dynamics of the complicated systems as
well as for the design of biocontrol strategies.
Responses to Variation in Host Plants and Landscape Structure
The dynamics of plant herbivore interactions
and herbivore population sizes depend on the spatial-temporal variation
within a system.
In a 10 year study of forest tent caterpillar dynamics,
Roland has found that forest fragmentation decouples caterpillar growth
from their classic growth regulators (parasitoids and viruses). As
a result, Roland has been able to provide a mechanism for the long-standing
observation of longer pest outbreaks in fragmented forests, potentially
leading to a solution to this problem of enormous economic importance.
Dale too is interested in the effects of plant spatial patterns on herbivore
populations, and is studying the effects of variation in the relative proportion
of preferred and non-preferred food plants on herbivore production.
Merrill has focused on understanding the effects of spatial-temporal variation
created by seasonal/annual dynamics in the environment on feedbacks in
plant-herbivore systems at different scales. For example, Merrill
has found that variation in plant phenology influences the long-term
dynamics of the elk-vegetation system in Yellowstone National Park.
At the landscape scale, both Merrill and Roland have shown that factors
influencing plant quality (season, isolation, patch size) influence animal
movement and feeding biology (Roland, Alpine Butterflies; Merrill, Elk
in Mt St. Helens). Merrill is using aerial videography to describe
spatial patterning of plants to understand herbivore movement and habitat
permeability in relation to landscape disturbances.
At the community
scale, Cahill has found that the movement of humans within a field influences
the diversity and abundance of insects within the field. Current
effort is focused on investigating the mechanisms behind such patterns,
and whether ungulate movement causes similar changes to insect diversity.
and Molecular Biology of Plant-Herbivore Defense
Plant-animal interactions are being studied
at the level of genes and proteins by members of the group.
A number of
projects aim to investigate the defensive biochemistry which mediates plant-animal
interactions. For example, collaboration between field and laboratory researchers
(Spence, Constabel) has identified key defense chemicals which are associated
with strong resistance of trembling aspen to forest tent caterpillar. Several
genes encoding defensive proteins have been isolated and characterized
from aspen and poplar. Using a collaborative approach and modern biochemical
and molecular tools, these are being studied directly for anti-herbivore
activity (Constabel, Keddie).
Plant transformation is being applied to
these genes and proteins, and their effects on herbivory can be assessed
in both transgenic crop and forest plants. Studies on defense gene expression
are providing detailed knowledge of how herbivore defense is regulated.
Many of the defenses are expressed only following attack, which implies
the existence of sensitive perceptive and signaling systems within plants.
Accumulated data suggests that a host of defense proteins and chemicals
are induced via a master regulator, and it may be possible to use this
switch to modulate the entire defense response. A goal of a related line
of research is to relate sub cellular processes of induced responses within
the plant to ecological processes in the field (Cahill, Constabel).
of Plant-Animal Interactions
Several member of the working group are
interested in understanding the evolution of plant-animal interactions.
Addicott focuses primarily on
mutualisms (aphids and ants, yuccas and yucca moths, and figs and fig wasps),
with experimental tests and computer models designed to determine what
processes regulate the costs and benefits of cooperative interactions,
under what conditions should individuals fail to cooperate and cheat, and
how cooperative interactions vary as a function of the environment, density
of the species, and quality of the species. Addicott’s work has been
central to the recent realization amongst ecologists that mutualisms are
a common and vastly understudied form of plant-animal interactions.
Sperling is interested in the phylogenetic study of the origin of plant-animal
interactions. A significant component of which is in understanding
the patterns of coevolution of insects and plants – specifically many plant-pest
combinations of economic importance.
Spence and Hik have conducted
numerous studies into how plants adapt to being eaten by insect (Spence)
and vertebrate (Hik) herbivores. They have specifically focused on
the long-term changes and adaptations by plants in response to herbivory
(chemistry, morphology, physiology), including the finding that long-term
grazing may result in overcompensation – with increased plant growth when
eaten compared to plants without herbivores.
One of the least understood areas of biology
are the interactions between microbes, plants, and associated animals.
Currah’s main research focus is in understanding the biology and distribution
of mycorrhizal fungi - whose reproductive structures are a source of food
for many animals. Currah is also examining the food-vector relationships
among wood decaying fungi and a variety of animal species. Micro-
and mesofauna that rely on standing and fallen timber for habitat, carry
decay and disease-causing fungi from site to site, facilitating the establishment
of pathogenic and decomposer species that, in turn, soften the wood and
serve as food for invertebrates.
Keddie is studying how the microbes
naturally found associated with plant roots may impact insect populations.
Little is known about the functioning of the soil community, how it changes
through space and time, whether plant chemistry impacts the level of severity
of any associated diseases, and whether some of these microbes act as forage