Specific Research Projects
|
My current projects can be broadly divided into 'field-based', and
'conceptual' (theoretical), although in many cases there is significant
overlap between the two. In the following I outline some of the
specific field-based research projects I'm working on at the moment.
|
|
Trophic Dynamics and Plant-Herbivore Interactions - The Snow Goose
Study
|
I am currently a collaborator on a large, multidisciplinary ecosystem
study (the Hudson
Bay Project), which focusses on the interaction of a keystone
herbivore (the lesser
snow goose) on the coastal ecosystem in breeding areas in the Canadian
sub-Arctic. Much of this work is centred on the long-term study at La
Pérouse Bay, Manitoba (LPB).
Snow Geese are a colonially nesting species, with extremely strong natal
philopatry amongst females, with strong tradition in their use of nesting
and feeding areas. Such breeding and foraging patterns reflects, to a
significant degree, a strongly synergistic relationship between
herbivorous geese and their principal salt-marsh food plants. Under
moderate grazing pressure, there is a positive feedback between grazing
intensity and fecal nitrogen deposition and both net above-ground primary
production and nitrogen content of food plants.
|
|
|
In general, grazing pressure over
the course of the breeding season reduces both above-ground forage and the
capacity of vegetation to show compensatory growth following grazing.
However, the size of the LPB
population has nearly
doubled in the last 15 years, and high-intensity
grazing and early-season grubbing by increased numbers of geese has
significantly reduced the annual standing crop of food available at LPB
since the beginning of the study. This has had significant long-term
negative
impacts on both the plants, and the geese. This rapid deterioration of conditions over a comparatively short time
span, and the seasonal variation in food supply,
creates a behavioral
conflict: at the one extreme, birds can remain philopatric to specific
nesting or feeding areas, regardless of predictable or unpredictable
changes in environmental conditions.
|
|
While there is clearly potential for
reduced fitness through poorer growth and survival of offspring, these may
be balanced by the advantages normally associated with philopatric
behavior (e.g., minimizing costs of moving to a new area). On the other
hand, dispersal becomes an adaptive strategy when the local environment
changes over time.
I am collaborating on a study to consider the various
factors which contribute to the responses of the geese to
the changing habitat. While most herbivory models assume
that the impact of grazing on plants is either neutral
(over some range) or strictly negative, it is of interest
to consider the dynamics of a system if low to moderate levels of
herbivory is
beneficial to vegetative plant growth. Such a positive impact on plants
has been clearly demonstrated for snow geese.
In a preliminary study,
we showed that the dynamics ranged from stable limit cycles to
globally-stable systems, depending primarily on the way in which the
frequency-dependent impacts of the geese on the plants were modeled. When
the positive effects of herbivores on the vegetation is dependent on the
amount of vegetation, locally-stable limit cycles are formed. In contrast,
when the positive effects of herbivores on the vegetation is independent
of the amount of vegetation available, globally stable equilibria are
generally observed. While this suggests that a stable equilibrium is
possible, the necessary conditions (which correspond to foraging only
within a finite area rather than in a spatially random fashion) are
unlikely to exist for snow geese, which do not exhibit territorial grazing
behaviours during brood-rearing. However, the situation is complicated
when multiple food plants are introduced into the model - preliminary
results suggest
that multiple food types may induce a stable
equilibrium even when foraging is near-random spatially.
|
Dynamics of an Emerging Pathogen in an Introduced Host
|
A large, multi-disciplinary study (coordinated by the Cornell Lab of Ornithology) to
investigate the interactions between
an emerging pathogen (Mycoplasma gallisepticum - MG), and an
introduced host (the common House Finch). This is a novel model system for
studying host-disease interactions, from a variety of perspectives:
Effects
of Disease on Host Population Dynamics. There is growing interest in
the suggestion that diseases can limit or regulate host populations, but
studies
are hampered by the logistical difficulties of quantifying simultaneously
prevalence of disease and host abundance over large geographic areas. This
limitation is not present in our system, in which clinical signs of
disease are obvious by visual inspection.
| |
|
Effects of Patchiness and Density of Host Population on Disease
Persistence. Potential disease hosts, human and otherwise, often live in
aggregations. The degree of aggregation and the extent of movement between
aggregations will affect the rate of spread of disease.
Effects of Sociality of Hosts on Spread of Disease. Current models of
host-
pathogen systems assume non-social hosts, which is not an accurate
reflection
of the social system of many animals. House finches alter their social
system
between breeding (paired, with young) and non-breeding (large flocks)
periods.
This contrast within a single species will allow us to determine the
effects of
social behavior on spread and maintenance of a pathogen, and study the
possible
impact of seasonal variation on disease prevalence.
|
Sources of Uncertainty in Harvest of Structured Populations
 |
Population dynamics are in simplest terms governed by the balance between
realized fecundity and recruitment, and mortality (or permanent
emigration). For harvested species, this poses the potentially complex
problem of determining the harvest practice which, by some criterion, is
determined to be "optimal". Optimality decisions are generally derived
with reference to the conditions under which population growth is
maintained at some sustained equilibrium, either naturally, or through the
harvest itself. The calculation of the optimal harvest conditions are
often complex, especially where harvesting is variable with respect to
time.
|
|
Many analyses of optimal harvesting assume
no age-structure, and
continuous time. However, for many populations, this assumption of no
age- or stage-structure, and continuous time, is clearly unrealistic.
Failure to account for this can contribute significantly to sources of
uncertainty, which affects our ability to successfully manage the
resource.
Preliminary analysis indicates failing to adequately account for structure
in the harvested population can lead to unpredictable results in some
cases.
This result also has significant
implications for biodiversity and management of resources, since it allows
a flexible framework to assess the relative importance of individuals of a
particular age or stage, and in a particular location, to a complex
structured system. This is increasingly important in
assessing viability of populations in fragmented landscapes.
|
Evaluation of Sterilization as a Method For Control of Urban Deer
|
The problem of effective control of species regarded by various criteria
as overabundant is of increasing concern to managers. Culling and
sterilization are generally thought to be to methods of direct management
control for nuisance species. Culling (permanent removal of some number of
individuals from the population) is clearly the most direct approach to
population control. However, it is often unpopular and difficult to
implement in many situations. In such cases, non-lethal fertility control
has been considered as a more tractable alternative. The impacts of such
fertility controls can vary from permanent (which is analogous to
demographic death), to transient (where the effects of the contraception
are less than the life-time of the treated individual animal). We will be
comparing the
relative efficacy of both culling and sterilization approaches to
population control, using a combination of population models, and field
trials. In collaboration with the Cayuga Heights Deer
Project, we
propose
to implement an adaptive management plan to explore the relative utility
of sterilization as a control method for overabundant wildlife, using a
suburban deer herd as a model system. While clearly the general problem of
over-abundance will require a variety of different approaches, the
particular problems of control of deer in urban and suburban areas are
somewhat specific.
| 
|
|
|
