Programme (4 - 8 November 2000)
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| 18.00 | Bus leaves from the department in Helsinki |
| 20.00 | Estimated arrival time at Tvärminne Zoological Station |
| 20.30 | Light evening meal |
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| 9.00 - 10.00 | Breakfast |
| 10.00 - 10.10 | ILKKA HANSKI: Opening words |
| 10.10 - 11.00 | CHRIS COSNER: Factors influencing local extinctions in habitat fragments: some hints from simple spatial models |abstract| |
| 11.00 - 11.30 | Coffee break |
| 11.30 - 12.15 | KENT HOLSINGER: Demography and extinction in plant populations |abstract| |
| 12.15 - 13.00 | BERNT-ERIK SAETHER: Predicting time to extinction in passerine bird populations |abstract| |
| 13.00 - 14.00 | Lunch |
| 14.00 - 14.30 | JOHAN KOTZE: Range size-body size relationships and the status of carabid beetles in Belgium, Denmark and the Netherlands |abstract| |
| 14.30 - 15.15 | GRANT HAMILTON: Population system persistence in a catastrophic system: the wild rabbit in arid and semi-arid Australia |abstract| |
| 15.15 - 15.45 | Coffee break |
| 15.45 - 16.30 | ANTHONY IVES: Extreme cycles in the dynamics of midges in lake Myvatn: the possibility of resource-consumer cycles |abstract| |
| 16.30 - 17.15 | JÖRGEN RIPA: On stochastic population models and the route to extinction |abstract| |
| 18.00 | Workshop dinner |
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| 8.00 - 9.00 | Breakfast |
| 9.00 - 10.00 | MICHAEL WHITLOCK: Genetic load and extinction in small and subdivided populations |abstract| |
| 10.00 - 10.15 | Coffee break |
| 10.15 - 11.00 | LAURENCE LOEWE: How many beneficial mutations are needed to stop Mullers Ratchet in MTDNA? |abstract| |
| 11.00 - 12.00 | STEINAR ENGEN: Migration and spatio-temporal variation in population dynamics in a heterogeneous environment |abstract| |
| 12.00 - 13.00 | Lunch |
| 13.00 - 14.00 | JORDI BASCOMPTE: Environmental stochasticity and metapopulation extinction |abstract| |
| 14.00 - 14.30 | Coffee break |
| 14.30 - 15.30 | OTSO OVASKAINEN: Stochastic versus deterministic metapopulation models |abstract| |
| 15.30 - 16.15 | WOLFGANG WEISSER: Extinctions in aphid metapopulations |abstract| |
| 17.00 - 18.00 | Dinner |
| 18.00 - | Sauna |
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| 8.00 - 9.00 | Breakfast |
| 9.00 - 10.00 | ILKKA HANSKI: Time delays in metapopulation dynamics and the extinction debt in communities |abstract| |
| 10.00 - 10.30 | Coffee break |
| 10.30 - 11.15 | BOB O'HARA: Uncertainty, stochasticity and more stochasticity in estimating the extinction risk of metapopulations |abstract| |
| 11.15 - 12.00 | MIKKO HEINO: Extinctions in temporally correlated environments |abstract| |
| 12.00 - 13.00 | Lunch |
| 13.00 - 13.30 | MAR CABEZA: Design of reserve networks and the persistence of biodiversity |abstract| |
| 13.30 - 14.00 | CHRISTOPH HAAG: Extinction in a Daphnia magna metapopulation |abstract| |
| 14.00 - 14.30 | Coffee break |
| 14.30 - 15.15 | MIKAEL FORTELIUS: Ecological anatomy of an extinction event 10 million years ago |abstract| |
| 15.15 - 16.00 | JUKKA JERNVALL: Contribution of inferred abundance to evolutionary trends in the dental capability of western Eurasian ungulates |abstract| |
| 17.00 - 18.00 | Dinner |
| 18.00 - | Optional round table discussion |
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| 8.00 - 9.00 | Breakfast |
| 9.00 | Bus leaves from Tvärminne Zoological Station |
| 11.00 | Approximate arrival time in Helsinki |
Abstracts
Jordi Bascompte
Title:
Environmental
stochasticity and metapopulation extinction.
Abstract: In this talk I will present a general model of
a
metapopulation subjected to human induced mortality in stochastic
environments.
The model is particularly relevant to species with weak density
dependence,
spatial structure, high dispersal, and subjected to highly variable
biotic
conditions. I will extend well known theory on geometric mean fitness
to
obtain analytical expressions for the minimum number of local
populations
required for metapopulation persistence. These expressions provide a
clear
way to relate the magnitude of environmental fluctuations, the minimum
number
of local populations, and the maximum levels of human induced mortality
for metapopulation persistence. Different scenarios can be interpreted
under
this theoretical background, ranging from conservation biology, where
the
challenge is the preservation of the metapopulation, to biological
control,
where the challenge is the eradication of a pest.
Mar Cabeza
Title: Design
of reserve
networks and the persistence of biodiversity.
Abstract: Site-selection algorithms are used in reserve
design
to identify networks of sites which maximize diversity given some
constraints
(e.g. cost, total area, etc.). These algorithms are mostly based on a
snapshot
of species occurrence and they ignore the question of how well species
persist
in the selected sites. I will present a theoretical approach that
considers
spatiotemporal dynamics in order to assess effectiveness of
site-selection
algorithms in terms of species persistence. Once a set of sites is
selected
by a common algorithm, we apply a metapopulation model to simulate
species
occurrence through time. We look at the species extinctions at the
selected
sites in two situations: first, when all sites are included in the
simulation,
and second, when the non-selected-sites are excluded from the
simulation
(i.e. assumed to be destroyed if they do not become a reserve). The
distinction
is done to emphasize the importance of the non-selected sites for the
spatial
dynamics of the system. The results show that species persistence may
be
strongly dependent on patches not included in the selection. In
summary,
our results support the call for the integration of spatial population
modelling
in reserve network design.
Chris Cosner
Title: Factors
influencing
local extinctions in habitat fragments: some hints from simple spatial
models.
Abstract: The dynamics of a population inhabiting a small
habitat patch can be affected in various ways by factors related to
patch
size and geometry, the permeability of the patch boundary, the nature
of
the landscape between patches, and the dispersal characteristics of the
population. In the case of a single species or a small number of
interacting
species in a single patch it is often possible to gain insight into the
role of spatial effects via diffusion models. This talk will describe
some
of the unexpected predictions of reaction-diffusion models in the
context
of persistence or extinction of populations in a single patch. For
example,
changing conditions on the patch boundary in a way that would benefit a
population if it were alone can sometimes harm the population if it
competes
with another species. The change in boundary conditions can sometimes
cause
a reversal of competitive dominance which could potentially lead to a
local
extinction. There are a number of other such effects, some of them
surprising,
which emerge from the way that population dynamics and dispersal
characteristics
interact with patch size or boundary conditions. In many cases
geometric
aspects of the models can be accounted for via the principal
eigenvalues
of differential operators which describe the diffusion or other forms
of
dispersal of the population.
Steinar Engen
Title:
Migration and
spatio-temporal variation in population dynamics in a heterogeneous
environment.
Abstract: A continuous stochastic population model in
space
and time is presented. The model includes migration, spatially
correlated
environmental noise and accounts for spatial heterogeneity in habitat
quality
using a general spatial autocorrelation in the local carrying
capacities.
The model is analyzed by Fourier methods based on linearizations which
are
realistic when the population fluctuations are not too large. An
expression
for the spatial autocorrelation for the population density is derived
together
with some relatively simple relations for the scaling of these
autocorrelations
under the assumption that the migration rate is constant. For strong
local
density regulation, the spatial density pattern is approximately the
same
as the pattern of spatial heterogeneity in habitat quality. For weak
density
regulation the scaling increases with migration rate and distance and
is
approximately the same as the scaling of the environmental noise if the
migration rate and distance are large. A required distinction between
the
spatial autocorrelation function and the function describing the
spatial
variation in the synchrony of population fluctuations is made. The
effects
of migration distance, migration rate, heterogeneity in carrying
capacities,
strength of local density regulation as well as the magnitude and
spatial
autocorrelation in the environmental noise are discussed. Numerical
examples
illustrating the general findings are presented. If the carrying
capacities
are lognormally distributed in space, and individuals migrate in
subsequent
small steps, the model generates exactly a lognormal spatial
distribution
of abundances. For this model it is possible to derive the joint
spatial
and temporal autocorrelations, which in turn may be used to find
approximations
for the time to local extinction or quasi-extinction in areas of
different
sizes.
Mikael Fortelius
Title:
Ecological anatomy
of an extinction event 10 million years ago.
Abstract: The so-called "Vallesian Crisis" seen
in the mammal faunas of Western Europe at about 10 Ma is usually
described
as a local extinction event resulting in a significant (perhaps 50%)
reduction
in species richness. Critical analysis of the data suggest a dramatic
decrease
in sampling intensity at the same time, however, leaving the degree
(indeed,
existence) of reduction in species richness open to question. Despite
this,
and despite the lack of independent evidence for any major change in
the
environment at the time, the extinction event itself is not in doubt.
It
can be shown that the ecological composition of the mammal community
changed
markedly at that time, with disproportionate loss of the smallest large
mammal species of omnivores and carnivores, and general replacement of
native
lineages by immigrants from Eastern Europe and Asia, resulting in
considerable
reduction in endemism. The Vallesian crisis also marks the transition
in
Western Europe from an ungulate fauna dominated by rhinoceroses and
suids
to one dominated by horses and, especially, ruminants. Thus, a major
extinction
event did clearly take place, but the evidence from community structure
is considerably more robust and easier to interpret than are the
uncertain
species richness counts. This may be generally true of extinction
events
in the fossil record.
Christoph Haag
Title:
Extinction in
a Daphnia magna metapopulation.
Abstract: Daphnia magna occurs in thousands of
rockpools
in the archipelago of Southern Finland. The pools show a metapopulation
dynamic with frequent extinction and recolonisation, the overall yearly
turnover rate being approximately 20%. However, newly founded
population
have a considerably higher extinction risk (40%) than already
established
pools (15%). We have investigated two factors, which might explain this
pattern. First, we found evidence for strong inbreeding following
colonisation
events. In an experiment strong inbreeding depression in the presence
of
competition between inbred and outbred individuals led to the fixation
or
near fixation of the outbred individuals. In the absence of competition
inbreeding depression was less strong but of a total of 99 populations
seven
inbred and no outbred populations went extinct during a period of three
months. Second, less suitable pools might be colonised from time to
time
for a short period but more permanent populations might fail to
establish
in such pools. Indeed we found that the establishment of populations in
empty pools fails in most cases (20% success). If however limestone is
added
to empty pools, increasing the Ca++-content and buffering the pH, the
rate
of establishment increases to 80%. Our data suggest that both,
inbreeding
depression and water chemistry influence the extinction of local Daphnia
magna populations. In our future work we plan to follow these two
factors
over time.
Grant Hamilton
Title:
Population system
persistence in a catastrophic system: the wild rabbit in arid and
semi-arid
Australia.
Abstract: Local populations of wild rabbit in arid and
semi-arid
zones of Australia undergo frequent and widespread local extinctions
due
to highly irregular rainfall, but rabbit population systems persist
despite
this. In this system, instability results from environmental
catastrophes
that cause the distribution of resources per individual to fluctuate
widely.
A consequence of these fluctuations is that all suitable habitat
patches
are not occupied at any one time. In a system underpinned by recurrent
extinctions
on this scale, system persistence is driven by the potential for
recolonisation.
Previous studies have shown that two distinct, adjoining rabbit
population
systems occur in southern central Queensland, a panmictic western
system
and a structured eastern system. The high degree of genetic structuring
evident in the eastern system cannot be explained by traditional models
of isolation by distance or geographical barriers. Given that the
habitat
matrix between local populations is able to support small, transient
populations,
an extension of traditional modelling approaches is needed to explain
underlying
processes. The region was considered to be saturated with resource
patches
of varying quality, and connectivity among local populations was
modelled.
Model output was validated by regression against independent genetic
population
structure data, and explained over 80% of the variability within the
system.
Ilkka Hanski
Title: Time
delays
in metapopulation dynamics and the extinction debt in communities
Abstract: Metapopulation size responds with a delay to
perturbations,
such as a change in the structure of a fragmented landscape. In the
community
context, extinction debt refers to the number of species whose new
equilibrium
following environmental change is global extinction, but which haven't
yet
had time to go extinct. We have worked on deterministic spatially
realistic
metapopulation models, which assume a finite number of patches and
spatial
variation in patch areas and connectivities. The models assume some
relationship
between local extinction rate and patch area, and between colonization
rate
and connectivity. In a spatially realistic version of the Levins model,
the time delay is a product of four factors: the strength of the
perturbation,
the ratio between the metapopulation capacity of the landscape and the
threshold
value set by the properties of the species, the characteristic
population
turnover rate, and an additional factor determined by the structure of
the
landscape. Time delay is especially long when the perturbation is
large,
when the species is close to the threshold for persistence, when the
characteristic
turnover rate is slow, and when there are only a few dynamically
important
patches in the network. In communities, the extinction debt is expected
to be especially great if many species are close to their extinction
threshold
following habitat loss. A corollary is that landscapes that have
recently
experienced substantial habitat loss and fragmentation are expected to
show
a transient 'overabundance' of rare species.
Papers:
Hanski & Ovaskainen, 2000, The metapopulation capacity of a
fragmented
landscape. Nature 404:755-758.
Ovaskainen & Hanski, Spatially structured metapopulation models:
metapopulation
capacity and threshold conditions for persistence. Manuscript.
Ovaskainen & Hanski, Time delay in metapopulation response to
perturbation.
Manuscript.
Hanski & Ovaskainen, Extinction debt at extinction threshold.
Manuscript.
Mikko Heino
Title:
Extinctions
in temporally correlated environments
Abstract: Most ecological models use white noise as the
null
model for environmental stochasticity, despite the increasing consensus
on that environmental variations tend to have positive temporal
correlations
("red"). However, including temporal correlations to stochastic
population models is not entirely trivial. Positively autocorrelated
red
environmental noise is characterized by a strong dependence of expected
sample variance on sample length. This dependence has to be taken into
account
when assessing extinction risk under red and white uncorrelated
environmental
noise. To facilitate a comparison between red and white noise, their
expected
variances can be scaled to be equal, but only at a chosen time scale.
Simple
one-dimensional population dynamics models show that the different but
equally
reasonable choices of the time scale yield qualitatively different
results
on the dependence of extinction risk on the colour of environmental
noise:
extinction risk might increase as well as decrease when the temporal
correlation
of noise increases.
Kent Holsinger
Title:
Demography and
extinction in plant populations.
Abstract: Populations subject to deterministic declines
are
certain to go extinct within a relatively small period of time, and the
time to extinction is relatively insensitive to the current size of the
population. Even populations that grow in size, on average, will
persist
for a relatively short time if the variance in annual growth rate is
more
than about twice the mean. As a result, isolated populations are not
likely
to persist indefinitely unless they are actively managed. A demographic
approach to management of rare plant populations suggests that
conservation
managers focus their efforts on those life-history stages between which
transitions most limit population growth. Demographic analyses of
long-lived
plants typically use matrix models to assess the sensitivity of mean
population
growth rates to changes in different life-history stages. Because the
variance
in growth rates cannot be ignored and because rare, catastrophic events
can have a large impact on persistence probabilities, however, analyses
of demographic models are better regarded as giving conservation
managers
tools to guide their intuition than as providing them with quantitative
estimates of persistence probability.
Anthony Ives
Title: Extreme
cycles
in the dynamics of midges in Lake Myvatn: the possibility of
resource-consumer
cycles.
Abstract: Midges, primarily the species Tanytarsus
gracilentus,
in Lake Myvatn, Iceland, show quasi-cycles of four orders of magnitude
with
a period of roughly 5-7 years. Time-series analyses suggest that these
cycles
are generated by consumer-resource interactions. T. gracilentus
is
a benthic filter feeder that reaches sufficient densities to eliminate
its
resource base. Analyses incorporating both population density and wing
length
(as a surrogate for resource availability) show the pattern expected of
consumer-resource cycles; fluctuations in density lag behind
fluctuations
in wing length. The analyses also demonstrate the importance of
accounting
for observation (measurement) error to describe midge dynamics
accurately.
Midges provide the primary food for several breeding bird populations,
and
understanding the processes causing midge outbreaks and crashes will
help
conservation management of these species.
Jukka Jernvall
Title: Contribution
of inferred abundance to evolutionary trends in the dental capability
of
western Eurasian ungulates.
Abstract: The advance of databases on large-scale
species-locality-occurrences
(SPLOC:s) offer a means to link ecological-level processes with
patterns
observed in palaeontological data. In recent communities, abundant
species
may contribute disproportionately to the community organization and
biomass.
While abundance is difficult to estimate from compilations of locality
data
directly, abundance can be approximated indirectly using the frequency
of
occurrence of taxa. Within a region and time-unit, fossil species
occurring
at many localities may be regarded as "common", and distinguished
from "rare" species with few locality occurrences. We used SPLOC:s
to test whether trends in the evolution of dental capability
(hypsodonty
times the number of cutting edges) differ between common and rare large
plant-eating mammals over the 20-million year interval preceding the
Quaternary
Ice Age. Initially, rare taxa show higher dental capability than common
taxa but the increase in dental capability is more pronounced in the
common
taxa. The trends for hypsodonty alone and for different aspects of
lophedness
are all shown stronger by the common species than by the rare ones. The
common taxa contribute only about 10% or less to the total species
list,
a proportion observable in recent communities as well. Therefore, to
the
extent that species-locality-occurrences reflect abundance, the
stronger
trends seen among common taxa may be more representative of the
community
level changes over the Neogene than the overall pattern. Conversely,
the
use of simple taxon presence lists may underestimate the
ecological changes inferred from palaeontological data.
Johan Kotze
Title: Range
size-body
size relationships and the status of carabid beetles in Belgium,
Denmark
and the Netherlands.
Abstract: The relationship between body size and range
size
is characteristically positive, i.e. larger species have wider ranges
than
smaller species. Range size and body size are also related to
probability
of extinction. For example, species of small geographic range size and
large
body size have been claimed to exhibit high probabilities of
extinction.
We tested these predictions using carabid beetles (Carabidae,
Coleoptera)
from three northern European countries; Belgium, Denmark and the
Netherlands.
There was no strong relationship between beetle range size and body
size.
However, carabid range, speciality, habitat preference and body size
strongly
influenced carabid beetle status (i.e. increasing, decreasing or
stagnant)
in these countries. Geographically restricted, stenotopic and small
beetles
are decreasing while geographically widespread, eurytopic larger
beetles
are generally increasing. Beetles in various dry habitats, i.e. dry
grasslands
and dry open habitats are decreasing while beetles in coastal and bog
habitat
are increasing in these countries. These results are discussed in
relation
to recent habitat alteration in Belgium, Denmark and the Netherlands.
Laurence Loewe
Title: How
many beneficial
mutations are needed to stop Mullers Ratchet in mtDNA?
Abstract: Recent observations of mitochondrial DNA in
pedigrees
revealed surprisingly high mutation rates. To reconcile these levels
with
significantly lower expectations based on phylogenetic analyses,
hotspots
and long-term removal of mutations by weak selection have been invoked.
The latter, however, would imply an increased genetic load. Together
with
recent estimates of slightly deleterious mutation rates in the human
genome
this may seem to endanger long-term survival. My simulations of such
populations
have shown that biologically meaningful sets of parameters exist which
do
lead to extinction, if only deleterious mutations, selection and drift
are
considered. However, this may be avoided by advantageous mutations.
These
may compensate directly for specific deleterious mutations or may lead
to
new capabilities improving fitness. Furthermore, compensatory
adaptation
in quantitative traits may prolong time to extinction or even prevent
deterioration
of absolute fitness at all. Different mutational effects and other
parameters
are explored by stochastic computer simulations in order to find the
critical
frequency of advantageous mutations necessary to stop Mullers Ratchet
under
these circumstances.
Bob O'Hara
Title:
Uncertainty,
stochasticity and more stochasticity in estimating the extinction risk
of
metapopulations.
Abstract:Predicting extinctions is an uncertain business.
Population dynamics are intrinsically stochastic. The environment is
also
stochastic, which adds to the stochasticity of the population. These
elements
of randomness arise from the stochastic nature of the world we observe.
But we should also consider uncertainties in the models we build, in
the
parameters of the models, and in the models themselves. I have taken
patch
occupancy data from Finnish butterfly metapopulations, and used
Bayesian
methods to fit a stochastic metapopulation model (the Incidence
Function
model) to the data. The parameter estimates are expressed as
probability
distributions, and these are used to make predictions about the time to
extinction of the metapopulations. The predictions give us a common
currency
to compare the different forms of variability. For the data,
predictions
are made for the model fitted both with and without environmental
stochasticity,
and for each of these, with both point estimates of the parameters
obtained
from the analysis (implying an assumption of complete knowledge about
the
parameters), and also from the full posterior distribution, which
allows
us to include our uncertainty in the parameter estimates in the
predictions.
The effects of these different forms of variability on the predictions
will
be discussed.
Otso Ovaskainen
Title:
Stochastic versus
deterministic metapopulation models
Abstract:Although real biological systems are of
stochastic
nature, deterministic models may in many cases give reasonable
approximations
for the observed phenomena. However, this is not always the case, and
deterministic
models should thus be applied with caution. I have studied spatially
realistic
metapopulation models (meaning that I take explicitly into account the
areas
and locations of the habitat patches, but ignore any further details)
both
through the deterministic and the stochastic approaches. The main
shortcoming
of the stochastic model is that the size of the problem increases as 2
to
the power of n, where n is the number of habitat patches. Consequently,
the stochastic model is not tractable (for anything but simulation) for
large n. On the other hand, the standard deterministic description of a
metapopulation lacks some of the most important features, such as the
assessment
of time to metapopulation extinction, and correlations in
patch-occupancy
probabilities. I demonstrate how the deterministic, spatially realistic
Levins model may be applied to give information about the
quasi-stationary
distribution of the corresponding stochastic model. I also demonstrate
how
the correlation structure induced by the stochastic model may be
incorporated
into the deterministic model. As an application, I study the effect of
spatially
correlated extinction risk.
Jörgen Ripa
Title: On
stochastic
population models and the route to extinction.
Abstract: This talk has two topics. First, I will discuss
how populations actually do go extinct, and what is predicted by
population
models. The focus question is whether populations go extinct from low
densities,
as we might think, or in catastrophic crashes from high densities, due
to
resource depletion. Models predict both, depending on the maximum and
density
dependence of the population growth rate and details in the population
growth
process. This analysis is performed by elaborate stochastic population
dynamic
modeling. Second, I will relate these results to what can be predicted
from
simple linear modeling and discuss the usefulness and possible
limitations
of linear models in theoretical population ecology.
Bernt-Erik Saether
Title:
Predicting time
to extinction in passerine bird populations
Abstract: Predicting time to extinction is of central
importance
in population viability analysis. Recently concerns have been raised
about
the practical applicability of such methods because of large
uncertainties
in model predictions. Such uncertainties arise from stochastic effects
on
the population dynamics as well as it may difficult to obtain accurate
estimates
of essential model parameters Here we introduce the term Population
Prediction
Interval (PPI) to quantitatively account for such uncertainties. A PPI
is
a stochastic interval that includes the unknown variable to be
predicted
with probability (1- p), where p is the cover
probability.
A prediction interval may be considered similar to a confidence
interval
in statistics, except that we draw inference about a stochastic
quantity
rather than a parameter. We illustrate how different parameters (e.g.
strength
of density regulation, specific growth rate, demographic and
environmental
stochasticity) as well as the uncertainty in them affect the prediction
of time to extinction in small passerine populations.
Wolfgang Weisser
Title:
Extinctions
in aphid metapopulations.
Abstract: Meta-populations of many aphid species are
characterised
by frequent extinction and colonisation events. Extinctions may occur
at
several spatial scales, on the level of individual plant ramets (aphid
'colonies'),
on the level of the plant (genet), on the level of isolated sites with
a
number of genets, and also at higher spatial levels. While the rates of
extinctions are higher than in many other described metapopulations,
the
causes of population extinctions are often difficult to establish.
Using
the aphid species Metopeurum fuscoviride, Macrosiphoniella
tanacetaria,
and Acyrthosiphon pisum as model organisms, the causes of
extinctions
are investigated, on the level of individual aphid colonies.
Experimental
evidence is presented to show that natural enemies can play an
important
role in aphid extinctions. In contrast to the results from these
experimental
manipulations, however, non-manipulative field studies often fail to
find
clear evidence for an involvement of natural enemies. Thus, the
quantitative
importance of natural enemies, and in fact of other extinction
mechanisms,
mostly remains unclear in population studies of aphid-predator systems.
This raises the general question how population studies with the aim to
determine the importance of extinction factors should be performed. For
insect predator-prey systems, is seems that a number of general
methodological
problems currently hinder quantitative studies of extinction causes.
Michael Whitlock
Title: Genetic
load
and extinction in small and subdivided populations.
Abstract: Beyond the identification of taxa and evolutionary
units,
the main contribution of genetics to conservation biology has been the
recognition
that the accumulation of deleterious alleles due to genetic drift in
small
populations threatens the continued persistence of endangered species.
Here
I extend previous results on the fixation of deleterious alleles to
include
the effects of compensatory and beneficial mutations, sexual selection,
and population structure. Beneficial and compensatory mutations can, in
populations larger than a certain effective population size, maintain
fitness
at an equilibrium which should allow the continued persistence of
populations.
Based on good guesses about certain unknown genetic parameters, this
critical
effective size may be relatively small, in the hundreds or thousands.
Furthermore,
the effects of new mutations are likely to also include effects on
mating
success (as demonstrated by some new data from Drosophila), and I sow
that
this effect can substantially reduce the load due to new mutations. In
contrast,
the subdivision of a species into geographically separated populations
can
result in a higher rate of fixing deleterious alleles and therefore
extinction.
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