Abstracts
Oral Abstracts
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SPATIAL VARIATION IN THE
RELATIVE STRENGTH OF TOP-DOWN AND BOTTOM-UP CONTROL: CAUSES AND
CONSEQUENCES FOR PHYTOPHAGOUS INSECT POPULATIONS
Robert F. Denno & Danny LewisDepartment of Entomology,
University of Maryland, 4112 Plant Sciences Building, College Park,
Maryland 20742, USA.
Most ecologists acknowledge
that both natural enemies and host plant resources act in concert to
control populations of insect herbivores. What is poorly known is how
the strength of top-down and bottom-up control vary spatially and what
factors dictate the relative strength of these forces. Here we review
factors such as host plant quality, vegetation texture, physical
disturbance, and subsidies (allochthonous resources and predators) from
neighboring habitats, all of which are known to alter the relative
strength of top-down and bottom-up control. Using a salt marsh system
as a model, we assemble new data with published information on effect
sizes to demonstrate how spatial variation in the above factors
integrate to produce landscape-level variation in the strength of
top-down and bottom up control. We develop a simple graphical model
that integrates spatial variation in top-down ad bottom-up variables to
make explicit habitat-related predictions concerning herbivore
abundance. The model predicts and field surveys verify that increased
disturbance, as it directly and indirectly influences herbivores
populations, shifts the balance from top-down to bottom-up control.
Based on habitat/vegetation characteristics as well as on variation in
the life history traits and behavior of predators and prey we attempt
to extend our findings and make general predictions as to the
probability for when and where bottom-up and top-down forces will
predominate.
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QUANTITATIVE FOOD WEBS AND
INDIRECT INTERACTIONS:
H Charles J Godfray &
Rebecca J Morris HOW TO ADD A SPATIAL COMPONENT NERC Centre for Population
Biology, Imperial College London, Silwood Park Campus, Ascot Berks, SL5
7PY, UK.
Natural communities contain
many interacting species and are spatially extensive. Programmes to
understand these two complexities have naturally tended to concentrate
on one or the other; for example, studies of the metapopulation
structure of one or a few interacting species, or studies of food web
structure at single locations. We will begin by describing how the
construction and analysis of quantitative food webs (from a single
locality) can suggest hypotheses about the processes structuring
ecological communities. In a quantitative food web, which typically
describes a guild of interacting species, all species and interaction
links are expressed in the same units. The hypotheses that emerge can
be tested by field manipulation experiments, and we will illustrate
this with examples from our work on host-parasitoid communities. We
will then discuss how this research programme can be extended to
include a spatial component; the logistic challenges that this will
entail, and the type of ecological questions it may help understand.
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EVOLUTION OF HOST PLANT
SELECTION AND DISPERSAL IN METAPOPULATIONS
Ilkka Hanski Department of Biological and Environmental Sciences, University of Helsinki, PO Box 65, FI-00014 Helsinki, Finland. In real landscapes, evolution
will not be driven solely by local (within-population) processes but
also by processes acting at the metapopulation level. The latter
processes can be critically influenced by spatial variation in habitat
quality and quantity. I will discuss two examples drawn from our
long-term study on the Glanville fritillary butterfly (Melitaea cinxia) in the Åland
Islands in Finland. First, spatial variation in the host plant
composition among the habitat patches influences the rate of
immigration of butterflies with dissimilar host plant preferences to
these patches. The biased immigration influences the relative use of
the host plants in local populations but also the rate of colonization
of currently unoccupied habitat patches. The biased colonization rate
in turn imposes a metapopulation-level selection pressure that will
influence the evolution of host plant preference. Second, the
phenotypic composition of local populations in terms of the mobility of
female butterflies is influenced by the age and spatial connectivity of
populations. Landscape structure will thereby influence the evolution
of dispersal rate, and spatial variation in landscape structure becomes
a powerful mechanism maintaining variation in dispersal rate and
correlated life history traits.
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MODELING
THE SPATIAL AND TEMPORAL DYNAMICS OF INSECT OUTBREAKS IN A COMPLEX
MULTITROPHIC SYSTEM
Susan
Harrison, Alan Hastings & Donald StrongDepartment of Environmental Science and Policy, Section of Evolution and Ecology, University of California at Davis, Davis, CA 95616, USA. To fully
understand the complex spatial and temporal behavior of outbreaks, models must go beyond simple plant-herbivore
dynamics and consider dispersal, trophic complexity, environmental
heterogeneity,
and their interactions. We will examine
these factors in models of the bush lupine - tussock moth - ghost moth
system.
Bush lupines (Lupinus arboreus) in coastal dunes in
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| THE ROLE OF PLANT CHEMISTRY IN
REGULATING PHYTOPHAGOUS INSECT POPULATIONS Erkki Haukioja Section of Ecology,
Department of Biology, University of Turku, FI-20014, Turku, Finland.
Plant defenses may contribute to population levels, and to population fluctuations, of herbivorous insects, and thereby to their spatial patterns. However, time series models have repeatedly indicated that parasitism, not plant defense, do explain changes in population density. I’ll concentrate on two problems, and on their consequences, in the above logic. First, plant defense levels are hard to quantify because plant “defense” is the outcome of three interactive systems: nutrients, secondary compounds, and specific plant defense cascades. Accordingly, there exist no data that would quantify plant defenses in different phases of population cycles. Second, plant quality interacts at least in two ways with parasitism: herbivore-induced plant volatiles attract parasitoids, and the immune defense of defoliators themselves depends on the quality of their host individuals, and on previous damage to these. Short-distance spatial variation in plant quality, or plant defense, is well documented within and among plant individuals. Plant defenses also offer more hypothetical but still plausible mechanisms for large-scale spatial phenomena. For instance, the role of herbivore-induced volatiles in triggering defenses in other plant individuals is well known, but the extent of these mechanisms in natural plant populations is open. Similarly, some environmental factors, like UV-B, switch on large numbers of the same genes which are also involved in specific defense cascades, offering a possible mechanistic basis for large-scale spatial synchrony in population phenomena. |
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GEOGRAPHICAL
VARIATION IN DENSITY DEPENDENT
DYNAMICS IMPACTS THE SYNCHRONIZING EFFECT OF DISPERSAL AND REGIONAL
STOCHASTICITY
Andrew
M. Liebhold1,
Ottar 1
Spatial synchrony refers to
coincident fluctuations in abundance among
spatially disjunct populations. In
recent years, there has been growing evidence of spatial synchrony in
populations of virtually every type of organism, though the magnitude
and
geographical range of synchrony may vary considerably. Theoretical
models have demonstrated that
populations may be synchronized either by small amounts of dispersal
between
populations or by the actions of small but synchronous random effects,
such as
that caused by weather (this is the so called “Moran effect”). In previous studies of this type, it has been
assumed that populations are primarily determined by density dependent
effects
and that dispersal and/or stochasticity represents a relatively minor
effect. However in virtually all of
these previous simulations, it has been assumed that the
density-dependent
processes affecting populations are identical among various populations. In this paper we use historical
spatially-referenced data on gypsy moth, Lymantria
dispar, outbreaks to document that density dependent processes can
vary
substantially among geographically disjunct populations.
This variation may be due in part to
geographical variation in the habitat (e.g., variation in forest
composition). We used both linear and
non-linear models to explore how among population variation in density
dependent processes affects synchronization via either synchronous
stochastic effects
or dispersal. While results generally
support the conclusion that geographical variation in density
dependence,
serves to diminish synchrony, we were surprised to find that simply the
type of
density dependence (even when it is identical among populations) can
play an
equally important role in determining the level of synchronization. Most importantly, the degree to which
populations oscillate in a periodic fashion strongly affects
synchronization,
though this effect varies when sychronization occurs via dispersal vs.
when it
is caused by stochastic effects. We
conclude that studies that attempt to explain synchronization among
populations
should carefully consider the nature of local density dependent
processes and
how these processes vary geographically. |
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PREDICTING LOCAL ADAPTATION IN
HERBIVOROUS INSECT POPULATIONS
Susan MopperDepartment of Biology, 300 East
Saint Mary Blvd., University of Louisiana, Lafayette, Louisiana
70504-2451, USA.
Generalist insects can become
local specialists, even when host plants are sympatrically distributed.
Host race formation has evolved in diverse insect taxa and is driven by
phenotypic differences between spatially overlapping plant species. The
local environment interacts with plant genotype to alter phenology,
morphology, defensive compounds, and nutritional status. If
sufficiently strong, these selective traits overcome the forces of
dispersal and gene flow in an insect population, and create genetic
structure shaped by the host species. Compared to host race formation,
local specialization on conspecific plants is rare. Nonetheless, demes
do form within insect populations, and they occur in insects with very
different life history traits. Theory predicted that dispersal ability,
feeding mode, and mating system determined the deme formation potential
of an insect species. But the empirical data don't support theoretical
predictions. In fact, no general patterns have emerged that allow us to
forecast reliably in what insect taxa demes are likely to evolve.
Perhaps plant rather than insect traits hold the fundamental clues to
the evolution of fine scale adaptive structure. I will discuss how
wide-spread adaptive deme formation is, what conditions foster deme
evolution, and the central role that plants play in driving these
fine-scale evolutionary processes.
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| HABITAT FRAGMENTATION AT
DIFFERENT TROPHIC LEVELS Saskya van Nouhuys Department of Ecology and
Evolutionary Biology, Cornell University, Ithaca, New York, 14853, USA.
Metapopulation Research Group, Department of Biological and Environmental Sciences, University of Helsinki, Finland. Species experience landscape
differently depending on their needs and behaviors. At one extreme are
dispersive species, moving at such large scales that they do not
perceive a landscape as patchy, or species that experience a landscape
as continuous because they have a wide resource breadth. At the other
extreme are sedentary species that stay within a patch, and species
with extremely narrow recourse needs that are confined to a small
fraction of the landscape. Within a community species that interact,
even intimately, such as a host and a parasitoid, experience landscape
differently. As a consequence, important aspects of the persistence of
each species and their interaction happen on different spatial scales.
We expect that species at high trophic levels are more sensitive to
habitat fragmentation than species at lower trophic levels. But this
depends on the relative movement behavior and resource breadth of the
species. I will review evidence from empirical studies in the
literature, that high trophic level insect species that are sedentary
and have a narrow host range are most constrained by habitat
fragmentation.
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HOST SPECIFICITY AND SPATIAL
DISTRIBUTION OF TROPICAL INSECT HERBIVORES
Vojtech NovotnyInstitute of Entomology, Czech
Academy of Sciences and Biological Faculty, University of South
Bohemia, Branisovska 31, 370 05 Ceske Budejovice, Czech Republic.
Analysis of host specificity in
tropical insect herbivores is changing from data on insect distribution
obtained by canopy fogging and other mass collecting methods to data on
insect rearing and experimentally verified feeding patterns. Existing
data suggest that a minority of species in herbivore communities feed
on a single plant species when alternative congeneric hosts are
available. Thus, host plant range limits tend to coincide with those of
plant genera, rather than supra-generic taxa. These host specificity
patterns lead to downward revisions of previous, extremely high
estimates of tropical species richness. Further, they have implications
for large-scale spatial distribution of insect herbivores and can lead
to the revision of some current assumptions on high beta diversity of
tropical insects. Although differences in host specificity between
temperate and tropical forests are difficult to assess since data on
tropical herbivores originate from recent field studies whilst those
temperate derive from regional host species lists, assembled over many
years, no major increase in host specificity from temperate to tropical
communities is evident.
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| CYCLIC DEFOLIATING INSECTS IN
FRAGMENTED LANDSCAPES Jens Roland1, Brian van Hezewijk1,2, Subhash Lele3 1Dept. of Biological
Sciences, University of Alberta, Edmonton, Alberta, T6G 2E9, Canada.
2Agriculture and Agri-Food Canada, 5403 - 1st Avenue South, P.O. Box 3000 Lethbridge, Alberta, T1J 4B1, Canada. 3Dept. of Mathematical and Statistical Sciences, University of Alberta, Edmonton, Alberta, T6G 2G1, Canada. The duration of some insect
outbreaks has been shown to vary with the spatial configuration of the
landscape. Outbreaks of forest tent caterpillar last several years
longer in fragmented forests compared to in contiguous forests.
Fragmentation is shown to reduce parasitism and transmission of and
mortality from viral disease. Using statistical modelling, we assess
the effect of landscape on the density-independent, direct
density-dependent and lagged density-dependent components of population
change, and then relate these patterns to results of field studies on
the mechanistic effects of landscape on population processes.
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| OAKS AS MOSAICS FOR A
HOST-SPECIFIC INSECTS Tomas Roslin & Sofia Gripenberg Metapopulation Research Group,
Department of Biological and Environmental Sciences, University of
Helsinki, Finland.
Oaks in the genus Quercus have
been classic targets for studies on insect-plant interactions. But how
is the local interplay between an oak and its herbivores affected by
its spatial setting? And how important is spatial context as compared
to intraspecific variation in host plant quality? In this talk, I
summarise the results from a series of studies aimed at 1) describing
spatial variation in host plant quality, and 2) disentangling the
relative effects of spatial context and host plant quality on local
insect populations. I report patterns in the physical and chemical
attributes of oak leaves across several hierarchical scales, and
compare these findings to patterns in the distribution, abundance and
performance of oak-feeding insects. I conclude that from the
perspective of a specialist insect, individual oak trees form mosaics
of highly heterogeneous resource quality, whereas average quality
differs relatively little among trees. I end by discussing the
implications of these findings for ecological sampling designs, for the
evolution of local adaptations and for the metapopulation dynamics of
oak-associated taxa.
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| ISOLATION BY HOST, BY DISTANCE
AND BY LANDSCAPE FEATURES COMBINE TO INFLUENCE POPULATION GENETIC
DIFFERENTIATION IN CHECKERSPOT BUTTERFLIES Michael C. Singer & Brian Wee Integrative Biology, Patterson
Laboratories, University of Texas, Austin, Texas 78712, USA.
A cluster of recent studies
shows that genetic differentiation of insect populations as estimated
from markers of unknown function depends not only on spatial isolation
but also on differences in host affiliation. For example, in the
checkerspot butterfly Euphydryas
aurinia there are significant effects of distance independently
of host and of host independently of distance. However, there is an
interaction between the two: host effects explain a high proportion of
the genetic variance when two different hosts are used allopatrically
but a low proportion when the same two hosts are used sympatrically.
The nature of the interplay between effects of physical separation and
local adaptation seems at present to differ dramatically among insect
species and even among groups of populations that use particular hosts.
For example, using AFLP analysis of nuclear DNA in the checkerspot
butterfly Euphydryas editha,
we showed that populations in which insects feed on Castilleja had high isolation by
distance (IBD) and strong among-population genetic differentiation. In
contrast, populations where Collinsia
is the host showed no IBD and low genetic differentiation,
measured over a similar geographic area of about 1000km x 300km. This
difference may support the suggestion from a separate analysis of mtDNA
that Castilleja is the
original host of this insect species. Puzzlingly, a superficially
similar effect, in which insects on Castilleja
have high genetic variance, occurs at an entirely
different scale of 300m x 300m. Inter-individual variation was
significantly higher among larvae gathered from Castilleja compared with those
gathered from Pedicularis at
the same site, although there was no difference at all in mean insect
genotype on the two hosts. Larvae from Castilleja also had significantly
higher heterozygosity as individuals than those from Pedicularis. Butterflies at the
site didn't have strong preferences for either host species so we
suspect that the differences we measured were not present at
oviposition but developed as a result of differential larval mortality
during the first few days of feeding. |
| COEVOLUTIONARY MOSAICS John N. Thompson Department of Ecology and Evolutionary Biology, Earth and Marine Sciences Building , University of California, Santa Cruz, CA 95064, USA. As species coevolve, they adapt
and coadapt in different ways within
different populations. Local coevolution produces a small range of
coevolutionary dynamics that have now been well characterized in
theoretical
models and demonstrated in laboratory and natural populations. These
local
dynamics form the modules upon which the broader coevolutionary
dynamics of
species take place. As our understanding of the geographic mosaic of
coevolution has grown in recent years, it has become possible to
develop more
specific hypotheses and predictions on how pairs and groups of species
coevolve
across complex geographic landscapes. |
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SPATIAL SCALE OF LANDSCAPE
CONTEXT INFLUENCING LOCAL INTERACTIONS AMONG INSECTS, PATHOGENS AND
PLANTS
Teja TscharntkeAgroecology, University of
Göttingen,
Waldweg 26, D-37073 Göttingen, Germany.
Interacting
populations driving ecosystem processes
depend on the recruitment of organisms and species from source
populations in
the surrounding landscape. In simple landscapes, local stands may not
receive
the set of species necessary to realize the potential ecosystem
functioning. As
populations of interacting species are influenced at different spatial
scales,
which may be measured as different radii around the local population,
structural changes from small to large landscape radii will affect
species
differently. Here, I focus on case studies from our group on
populations of
plants, pathogens, phytophagous insects and their parasitoids as well
as
plant-pollinator interactions. Patterns of plant diversity are mostly
related
to local site conditions, but landscape context may also be important.
This is
shown here by analysing the relative importance of local site and
regional
landscape characteristics on local species richness of arable weeds.
More
details will be given for Creeping Thistle Cirsium
arvense populations. Changes in local plant densities with
landscape
context affect the resource basis for trophic interactions. Levels of
local
rust infection of Creeping Thistles appeared to be determined by larger
scales
of the surrounding landscape than the thistles’ populations. In
addition to an
overview on thistle insects and their relation to pathogens, landscape
context
of cereal aphid-parasitoid interactions is given showing that these
host-alternating aphids as well as their enemies profit from complex
landscapes. Analyses of local plant-pathogen-insect interactions need a
landscape perspective, but we are far from understanding the complex
mechanisms
driving populations of interacting species in real landscapes.
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COMBINING
MODELS AND DATA IN ANALYSING HERBIVORE-HOST PLANT INTERACTIONS During
the
seventies of the last century we
started a project on a (monophagous) insect herbivore-host plant
interaction
with periodic total defoliation. The aim was to test whether the
dynamics of
the system would fit a simple Lotka-Volterra oscillation model. Within
two
years, two out of three selected local host plant populations, and
consequently
those of the herbivore, became extinct. We realized that the system
could only
survive in a spatial configuration. Since then one hundred local
populations of
insect and plant have been monitored. Ignoring the spatial
configuration, on
the metapopulation level herbivore and host indeed can be described by
an
oscillation model. Delay of recovery of the herbivore after large-scale
metapopulation crashes, a delay which is probably crucial for host
plant
recovery, cannot be explained by food shortage. This delay runs
parallel to
relatively high parasitoid incidence. Models indicated that either a
better
dispersal capacity of the herbivore or a larger fecundity led to new
outbreaks
during which parasitism is reduced to almost zero. These models guided
experiments on parasitoid dispersal and on a molecular comparison of
herbivore
and parasitoid populations in a spatial context.
Finally we
will analyse herbivore-host plant interactions in spatially separated
systems
in different countries with and without parasitoids.
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METAPOPULATION DYNAMICS AND
GENETIC STRUCTURE OF MONOPHAGOUS INSECT HERBIVORES
Wolfgang W. WeisserInstitute of Ecology, Friedrich-Schiller-University, Jena, Germany. In patchy environments,
patterns of genetic variation will be strongly influenced by migration
between local populations and by local colonization and extinction
events. The aphid species Metopeurum
fuscoviride and Macrosiphoniella
tanacetaria are specialised herbivores on tansy, Tanacetum vulgare, a perennial
plant common along rivers, the coast and in wastelands. Due to clonal
growth, tansy plants (=genets) consist of one to many shoots (=ramets),
each of which can host an aphid colony. The habitat of tansy aphids is
therefore highly structured and aphids cluster in at least three
spatial scales: at the level of ramets, at the level of genets and at
the level of sites. (Sub)population turnover at all these levels is
very high, with persistence times in the order of weeks (ramet) to
months (sites), suggesting that migration rates should also be high,
resulting in little differentiation between populations. However, there
is high genetic diversity at all spatial levels and populations are
significantly differentiated, even over a small spatial scale. While
the ecological data appear to show that most dispersal occurs within
sites with little between-site migration, the genetic data suggest that
founder effects and genetic drift in small populations appear to
dominate the genetics of the metapopulation.
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Poster
Abstract
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SCALE-DEPENDENCE OF
PLANT-HERBIVORE INTERACTIONS: BARK BEETLES AND PINE TREES
Matt Ayres1, Tiina Ylioja2, Sharon Martinson1 and Brenda Whited1 1 Dartmouth College, Hanover, NH, USA 2 Metla, Finnish Forest Research Institute, Vantaa, Finland. When and why do ecological
patterns change character with spatial scale? We have begun exploring
some surprising changes across scale in the pattern of interactions
between bark beetles and their host trees. We compared the
susceptibility of Pinus taeda
and P. virginiana to Dendroctonus frontalis (Coleoptera:
Scolytidae) at two hierarchical scales: within heterospecific stands
(ca. 10x10 m) and across a forest landscape (72 000 ha) that was
dominated by monospecific stands. In the former, flying beetles
preferentially attacked P. virginiana
(tree mortality = 65-100% in P.
virginiana vs. 0-66% in P.
taeda), but in the latter, stands of P. taeda were more susceptible than
stands of P. virginiana. This
hierarchical transition in host susceptibility was predicted from
knowledge of (1) a behavioral preference of beetles for attacking P. virginiana vs. P. taeda, (2) a negative
correlation between host preference and reproductive success, and (3) a
mismatch in the domain of scale between demographics and host selection
by individuals. We have identified two additional incongruencies that
arise with changes in spatial scale: 1. Bark beetle populations display
strong positive density-dependence (Allee effects). The orthodox
explanation has been that large aggregations of beetles are more
successful in overwhelming tree defences. This is true for D. frontalis, but there turns out
to be no relationship between local population size and average attack
rates of individual trees. Thus, reproductive benefits of mass attacks
on individual trees cannot readily explain the higher relative growth
rate of large infestations. 2. Single species stands of Pinus palustris are strongly
resistant to D. frontalis
infestations even though individual longleaf trees within mixed species
stands do not seem any more likely to escape attack or survive attacks
than loblolly trees. Solving these puzzles should yield an improved
understanding of population dynamics in D. frontalis, and could aid in
developing a general approach for recognizing and understanding scaling
allometries in the demographics of other herbivores.
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THE IMPORTANCE
OF SPATIAL SEARCH BEHAVIOUR
Department of Zoology, How is a
herbivore population affected by changes in the abundance of its host
plant? If
the herbivore population is controlled by predators or parasitoids
which move
frequently between host-plants, then the answer depends crucially on
the
fine-grain spatial distribution of the host plants and the spatial
search
behaviour of the predators. Changes in the abundance of host-plants
will have a
non-linear effect on herbivore abundance that can be described in terms
of a
threshold of host-plant abundance. The size of this threshold is
determined by
the relative speeds with which the predator moves on host-plants and in
the
areas between the plants. As long as host-plant abundance remains above
the
threshold, then changes in host-plant abundance will have little impact
on the
number of herbivores on each plant. Below the threshold, however, a
reduction
in host-plant abundance will result in an increase in the number of
herbivores
on each plant. And the less direct the predator’s travel between plants
or
patches of plants, the more herbivore abundance will increase. These
results
suggest that the spatial abilities of individual predators and the
spatial
habitat structure modulate the relative strengths of top-down and
bottom-up
forces in controlling a herbivore population.
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| GENETIC
PATTERNS OF DIFFERENTIATION IN THE LARGE PINE
WEEVIL IN EUROPE C. Conord, L. Despres & G. Lemperiere LECA : Laboratoire d’Ecologie Alpine, Université Jospeh Fourier - |
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CONNECTIVITY
AND PATCH SHAPE CAUSE DIFFERENTIAL SEED
PREDATION
Ellen I. Damschen1 & John L. Orrock21Department
of Zoology,
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HOST PLANT QUALITY AND LOCAL
ADAPTATION AS
DETERMINANTS OF
THE DISTRIBUTION OF A GALL-FORMING HERBIVORE
S. P. Egan1,2 and J. R. Ott1 1Department of Biology, Herbivores exhibit a universal pattern of patchy distribution within populations of their host plants. We report on a manipulative transplant experiment that links host plant quality to herbivore fitness at the local scale with the process of local adaptation at the patch scale to provide a synthetic explanation to this pattern for the gall-forming herbivore, Belonocnema treatae, within populations of its host plant, Quercus fusiformis. Oak/gall-former systems support species-rich assemblages that offer model systems to study community ecology. Thus, a mechanistic explanation for the distribution of a gall-forming insect provides powerful insight into understanding the distribution of entire terrestrial communities. Mated B. treatae females from each of five high gall density trees were allowed to oviposit and their progeny subsequently develop on (a) their respective four nearest conspecific neighbors exhibiting low gall density, (b) the four alternative high density trees, and (c) their natal trees. Mixed-effects ANOVA was used to analyze seven independent estimates of insect performance. Results demonstrate, for the first time in a Cynipid -Oak system (>2 000 species), that (a) stable herbivore populations are isolated by low quality host trees and (b) local adaptation has taken place at the scale of individual trees. Thus, host plant quality and local adaptation act, in combination, as a driving force on the distribution of B. treatae and its diverse gall-dependant community (N = 27 species). |
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SPATIAL
VARIATION IN BIOTIC
INTERACTIONS AND FLORAL POLYMORPHISM
Johan EhrlénDepartment of Botany, |
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RELATIVE
IMPORTANCE OF RESOURCE
SIZE AND ISOLATION FOR LANDSCAPE DISTRIBUTION OF TWO MONOPHAGOUS
BUTTERFLIES
Jochen KraussInstitute
of Environmental
Sciences,
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FOOD
PREFERENCE
AND PERFORMANCE OF A
SPECIALIST HERBIVORE: SPATIAL VARIATION IN HOST PLANT QUALITY
Roosa Leimu & Marianna RiipiSection of Ecology, |
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MODELLING
VECTOR DYNAMICS AND THE
SPREAD OF INSECT-TRANSMITTED VIRUSES
Central Science Laboratory, |
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THERE'S
NO SUCH THING AS A FREE LUNCH: THE COST OF DEFENCE CHEMICAL
SEQUESTRATION IN A
LEAF BEETLE
Laboratoire d'Ecologie Animale et d'Entomologie, Université de Neuchâtel, Switzerland. |
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IMPACT OF
SHOOT
HERBIVORY ON A PERENNIAL HERB IN A
METAPOPULATION CONTEXT
Viktoria
Pettersson, Hans Gardfjell, Lars Ericson & Barbara E. GilesDepartment of Ecology and Environmental Science, Umeå University, 901 87 Umeå, Sweden. Silene
dioica is a
dioecious perennial herb and food source for two host-specific,
shoot-eating
herbivores. Larvae of the microlepidoptera Caryocolum
viscariella (Gelechiidae) attack reproductive shoots as they form,
spinning
together the upper leaves and eating the buds and upper parts of the
floral
stem. Larvae of the root-maggot fly Delia criniventri
(Anthomyiidae) tunnel
through the basal meristem to eat into the bases of the flowering
shoots. In
the Skeppsvik Archipelago, an area of rapid land uplift in the
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DOES TREE SPECIES DIVERSITY AFFECT SURVIVAL OF |
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SPATIAL
VARIATION IN HOST PLANT QUALITY IN THE MELITAEA CINXIA
METAPOPULATION
Spatial
variation in host plant quality within
and among populations may be caused, for example, by genetic
differences or
defence metabolites induced by exploitation by other species. This
variation
may affect the development and survival of insects feeding on them. In
the
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SPATIO-TEMPORAL
PATTERNS IN A HOST-ENEMY SYSTEM IN AN
ARCHIPELAGO
1 Dept. Ecology and Environmental Science, 2 Umeå Plant Science Centre, |
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GYPSY
MOTHS GO FOR A SWIM - THE SPATIAL ECOLOGY OF THE
INTERACTION BETWEEN ACENTRIA EPHEMERELLA
AND SUBMERGED MACROPHYTES
Dietmar Straile, Oliver
Miler & Michael KornLimnological Institute, Department of Biology, University of Konstanz, Germany. The
aquatic
moth Acentria ephemerella causes considerable
defoliation of
macrophytes, which are both food and habitat for Acentria.
Acentria mass
outbreaks and several characteristics of its biology (e.g., female
flightlessness, biased sex ratio) suggest that Acentria
can be considered as an aquatic analogue to the Gypsy
moth. Mesocosm experiments revealed that the absence of fish predation
is
probably a major determinant for mass outbreaks, especially since fish
predation results into male dominance. The latter because higher
predation on
probably more active females. Within the Special Collaborative Program
“Littoral of Lake Constance” we study several aspects of the macrophyte
- Acentria – fish tritrophic system. Using
remote sensing the patch dynamics and isolation of macrophytes is
studied. With
intensive field sampling programmes we analyse the seasonal and spatial
dynamics
of Acentria (and to a lesser extent
of fish). These data suggest that fish predation is reduced in small
and
isolated patches of macrophytes. In mesocosm and aquaria experiments
trophic
interactions and the life history of Acentria
is analysed.
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NOCTUID
MOTHS
FEEDING ON CATTAIL (TYPHA LATIFOLIA) AS A MODEL SYSTEM FOR
STUDIES ON
SPATIAL ECOLOGY OF HERBIVORES
Tiit Teder
& Toomas TammaruInstitute
of Zoology and
Hydrobiology,
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SIGNS OF
SELECTIVE MOSAIC IN THE
Outi Vesakoski, Veijo Jormalainen,
Tuija Honkanen
& Jenni RautanenSection of Ecology, FIN-20014, University of Turku, Finlan |
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HOST PLANT
POPULATION SIZE DETERMINE CASCADING EFFECTS IN A
PLANT-HERBIVORE-PARASITOID SYSTEM
Department of Botany, Stockholm University, S-10691, Stockholm, Sweden. |
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