Population Biology / Ecology III
Sunday March 13:
10:00am-11:30am
Back to Concurrent Session
III
ABSTRACTS |
DIFFERENCES IN GENERALIST AND SPECIALIST
RESPONSES:
BACK TO FIRST PRINCIPLES
(Honorable mention!)
Steury, T.D.1 and D.L. Murray2
1Dept. of Life Sciences, Indiana
State University, Terre Haute, IN 47809, USA
2Dept. of Biology, Trent University, Peterborough,
ON, K9L 7B8, Canada
The idea that generalist predators
should stabilize prey population dynamics while specialist
predators should destabilize prey dynamics is based
on an unrealistic assumption that predator diet breadth
can be dichotomized and such dichotomy leads to equally
distinctive types of functional and numerical responses.
Not surprisingly, few empirical tests of the disparity
in generalist and specialist responses have been successful.
We generated predictions regarding differences in
responses between predators with dissimilar diet breadth
but identical types of functional and numerical responses.
We then tested our predictions by fitting response
curves to published data for coyote (a generalist)
and lynx (a specialist) relative to hare density.
Supporting our predictions, the coyote exhibited lower
kill rates and higher density at any specific hare
density relative to that of lynx. Stability analysis
demonstrates that our predictions can lead to differences
in system stability as proposed by classic theory;
systems with predators characterized by relatively
broad diets are more likely to have stable point attractors
and may have greater ecological resilience. Thus,
the theory that generalists drive stability and specialists
drive instability can be supported in a relative sense
without dichotomizing predator diet breadth or invoking
associations between diet breadth and specific response
types.
Key words: Diet breadth; population
dynamics; predator response; stability
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COMPARATIVE PERFORMANCE OF LANDSCAPE-LEVEL
HABITAT MODELS FOR NORTHERN BOBWHITE IN ILLINOIS.
Dzimiela, J.J., A. Woolf, E.M. Schauber,
and J.R. Roseberry
Cooperative Wildlife Research Laboratory
and Department of Zoology, Southern Illinois University,
Carbondale, IL, 62901
In the past three decades, populations
of northern bobwhite quail (Colinus virginianus) have
declined considerably in Illinois and throughout their
range. Principal causes of population decline appear
to be loss and alteration of habitat due to modern
agricultural practices and rural development. Landscape-level
habitat modeling can be an efficient method of assessing
present amount and distribution of habitat. Two competing
bobwhite habitat models have been developed for the
state of Illinois. One model categorized 24% (35,000
km2) of Illinois as potentially suitable habitat whereas
the other categorized 49% (71,294 km2) of Illinois
as potentially suitable habitat. We compare the performance
of the two models by testing their habitat categorizations
against quail presence/absence data collected within
390 randomly located 250 ha-sample units stratified
by model categorization (suitable/unsuitable) and
physiographic region. Presence/absence data stem from
a mail survey of landowners within sample units. We
present comparisons of regional performance variation
between the two models throughout Illinois’
historic quail range. Also, land use and habitat management
data collected in the survey and its potential influence
on model performance will be discussed. The goal of
this study is to recommend an accurate habitat model
for agency use and to help focus upland management
activities and concerns to landscapes where they will
be the most cost-effective and produce the greatest
benefit to quail abundance.
Keywords: northern bobwhite, habitat
modeling, performance evaluation, landowner survey.
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EFFECTS
OF ASYNCHRONOUS HATCHING AND POPULATION DENSITY ON LIFE-HISTORY
TRAITS OF Melanoplus sanguinipes
Laws, A.N.
Department of Biological Sciences,
University of Notre Dame, Notre Dame, IN 46556
Many grasshopper species in temperate
regions exhibit asynchronous hatching. This is partly
due to the ability of grasshoppers to produce multiple
pods throughout a season, and to differences in ovipostion
site, such as temperature and soil moisture, that influence
hatching date. I conducted a manipulative field experiment
in western Montana to determine what effects asynchronous
hatching has on important life-history traits (survivorship,
body size, fecundity) of Melanoplus sanguinipes.
Second and third instar M. sanguinipes nymphs were stocked
into enclosures at 10 densities, that reflect the range
of grasshopper densities observed at my site. After
three weeks, half of the enclosures were restocked with
second and third instar M. sanguinipes nymphs
to simulate asynchronous hatching, while the other half
of the enclosures received no additional grasshoppers,
simulating synchronous hatching. Survival, reproduction,
and female body size exhibited density dependence in
both hatching treatments, indicating that intraspecific
competition is important at my site. Survivorship was
higher in the asynchronous hatching treatment than the
synchronous treatment (P < 0.05, ANOVA), and was
apparently driven by females, which out-competed males.
Though survival was higher in the asynchronous treatment,
body size was higher in the synchronous treatment at
low densities for females, and across all densities
for males. There was no difference in reproduction between
hatching treatments (P > 0.05, ANOVA), which was
probably influenced by the similarity in female body
size between hatching treatments at moderate to high
densities.
Keywords: grasshopper, asynchronous hatching,
life-history, density dependence
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BIOLOGICAL
CONTROL OF THE SOUTHERN PINE BEETLE USING THE CHECKERED
BEETLE Thanasimus dubius
Costa, A.
Department of Zoology, Southern Illinois
University, Carbondale, IL 62901
The southern pine beetle, Dendroctonus
frontalis (Coleoptera: Scolytidae), is known to
be a major pest of pine forests throughout the southern
US, inflicting considerable economic damages during
outbreaks. A common predator of bark beetles, Thanasimus
dubius (Coleoptera: Cleridae), has recently been
suggested to have a prevalent role on the dynamics of
this pest. This predator has been shown to affect prey
survival in both the larvae and adult stages, but further
tests using this predator as a biological control agent
are required to ascertain its impact on prey dynamics.
It might be used in a biological control program by
treating infested trees with T. dubius eggs.
Newly hatched predator larvae were set at several densities
on log bolts taken from pine trees infested by D.
frontalis. In order to assess the potential impact
of T. dubius larvae on prey survival, the number
of adult southern pine beetles emerging from the pine
log and the number of exit holes were measured. To produce
enough predators for such a study, the method previously
developed to rear T. dubius larvae on an artificial
diet was improved by adding preservatives in the larvae
diet, which reduces the overall number of feedings.
Yet, to insure this method is safe considering survival
and reproduction of predators, a study to measure potential
effects of preservatives and delay feeding time on predator
performance (larvae and adult mortality, female fecundity)
was conducted.
Key Words: rearing, preservative, predator
performance, biological control
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FOOD
LIMITATION AND COMPLEX DYNAMICS IN HERBIVOROUS INSECTS
Abbott, K.C.
Department of Ecology and Evolution,
University of Chicago, Chicago, IL 60637
Despite a vast body of work on consumer-resource
interactions, plant-herbivore theory has received little
attention. Traditional consumer-resource theory (predator-prey
and host-parasitoid models) use biological assumptions
which make them unsuitable for plant-herbivore systems.
As a result, the expected dynamics of food-limited herbivores
remain virtually unknown. Population outbreaks are common
in herbivorous insects, but in most cases, we cannot
identify the factor driving these dynamics. To determine
whether food limitation can drive realistic population
dynamics in herbivores, I consider a series of simple
and general population dynamic models which relate the
abundance of a host-plant to the abundance of its herbivore.
These models show that complex dynamics, such as outbreaks,
can be accurately predicted by changes in plant abundance
alone. This novel result demonstrates that neither inducible
defenses nor higher trophic levels, such as predators,
parasitoids, or pathogens, need be present for herbivore
outbreaks to occur.
Keywords: herbivory, insect outbreak,
consumer-resource model, population dynamics
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FOREST MATRIX PERMEABILITY TO BUTTERFLY
MOVEMENT IN A FRAGMENTED PRAIRIE LANDSCAPE IN SOUTH-CENTRAL
OHIO
Stasek, D.J. and Crist, T.O.
Department of Zoology, Miami University,
Oxford, OH 45056
The composition of the matrix (non-habitat)
surrounding suitable habitat patches is known to influence
movement patterns and the spatial structuring of a
species. Depending on the composition of the matrix,
a habitat patch may be isolated from other suitable
habitat patches, or the matrix may allow for easy
dispersal from patch to patch. Other factors such
as the distance between patches and the type of edge
(hard vs. soft) surrounding a patch will also influence
dispersal patterns and the spatial structuring within
a patch. Using three species of butterfly, we have
attempted to quantify the permeability of the matrix
and the habitat edge to movement between habitat patches
in a naturally fragmented system. The Lynx prairie
system in Adams County, OH consists of nine (9) remnant
prairie patches of variable sizes, variable distances
between patches, and variable matrix composition between
patches. Matrix composition ranged from herbaceous
vegetation to oak forest. Mark-recapture methods were
used to assess the movement patterns of the great-spangled
fritillary (Speyeria cybele, Lepidoptera: Nymphalidae),
the pearl crescent (Phycoides tharos, Lepidoptera:
Nymphalidae), and the pipevine swallowtail (Battus
philenor, Lepidoptera: Papilionidae). Direct observation
was used to determine the target species’ behavior
at a patch’s edge. Great-spangled fritillaries
exhibited the most movement between patches with 66%
of recaptures found in a different patch than the
one where they were initially marked. Pearl crescents
rarely left the patch where they were first marked
(71% of recaptures). Great-spangled fritillaries crossed
any type of edge and moved through any type of matrix,
while pearl crescents rarely approached or crossed
a patch’s edge. Insufficient recaptures of the
pipevine swallowtail did not allow for movement analysis,
but the type of edge was not a barrier to movement
in this species. Based on observed movement patterns,
the population of the great-spangled fritillary in
the Lynx system appears to be exhibiting metapopulation
dynamics, while each patch is an individual population
of pearl crescents. This study is important to land
managers because in order to manage species properly,
it must be known how much suitable habitat is necessary
for a given species.
Keywords: landscape ecology, Lepidoptera,
matrix, metapopulation
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III
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