Transcript Chapter9

• Prediction and therefore mitigation of existing invasions, and
the prevention of future invasions is possible in some
systems.
• Advances in computer software programmes for modelling
and database management (e.g. Genetic Algorithm for Rule
Set Prediction, GARP) are already enabling scientists to
provide resource managers and policy makers with
projections of the potential range and impacts of IAS, thus
helping them to make better informed decisions (Meyerson
and Reaser, 2003).
RICCIARDI & RATHMUSEN’S (1998) GUIDELINES:
• Identify potential donor regions and dispersal pathways of future
invaders
• Select potential invaders using biological criteria
• Use invasion history as a predictive criterion
The prediction of future invasions has often been poor
Different methods have been used which are based on either a
species-oriented view (invasiveness) or a habitat-oriented view
(invasibility).
>> HTML Notes
MACK (1996) ANALYSED 8 DIFFERENT METHODS
1. Compilation of species that have been weeds in their home range
or elsewhere – the most straightforward approach but the
limitation is that it is restricted to species with a record of
invasiveness
2. Compilation of the traits of invading species – Baker (1974)
compiled the most well known list of characteristics of an “ideal
weed”. Limitations: no one invader has (or could have) all the
features proposed for ideal weeds; indeed, many invaders have
very few of these features. Many other species that have not
become extensively naturalised display many of these traits, such
as wheat and barley
3. Invasive potential based on similar climates – Climates in the
home ranges of potential invaders have been used as guides to
new, potential regions of infestation.
Johnston (1924) estimated the direction of future advances for
several alien cacti in Australia based on the climates of their
home ranges.
Limitations: the new (or even indigenous) range of a species
may not exhibit the entire suite of climatic features that it can
tolerate. Climate is also only one part of the environmental
complex to which organisms respond
4. Experimental manipulation of the environment (controlled-growth
chambers) – An alien species can be assessed under a wide
range of conditions under which it is not currently found, in order
to gauge the scope of any new range. Limitations: only assess a
few physical parameters. Restricted to a few life-stages
5. Detailed comparisons among congeners – comparisons among
species that are all alien in a new range, and comparisons
between an indigenous and a congeneric alien in the same range.
Limitation: not all species that enter a new range have closelyrelated congeners
6. Experimental sowings (no manipulation of the environment).
Limitation: the factors that apparently restrict the range may
operate infrequently
7. Experimental sowings (with manipulations of field conditions) –
makes use of smoke-pots, bird-netting, irrigation, pesticides,
surrounding seedlings with gravel to reduce frost damage, etc.
Variable amounts of “environmental conditions” are used to test
those that are the most important factors in invasion.
Limitation: the factors chosen for manipulation may not include
those contributing most to the naturalisation/extirpation of an
alien species.
8. Mathematical models to predict
the course of plant invasions
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MODELS
• A framework for the prediction of alien plant spread requires the
development and refinement of mathematical modelling tools.
The objective of any modelling effort is to simulate the system of
interest as accurately as possible (Killion and Grant, 1995).
• Higgins and Richardson (1996) provide a good review of models
used in predicting alien species spread. However, these models
are mostly applied to invasive plants, because plants are easier
to model – they don’t get up and walk away!
A CONCEPTUAL MODEL OF ALIEN PLANT SPREAD
• Auto-ecological attributes, which determine invasive success
(life history, eco-physiological attributes)
• Environmental resource fluctuations (resource availability and
disturbance). Resource availability includes factors such as
nutrient, moisture and space availability
• Plant-environment interactions
• Demography
• Alien abundance
• Feedback (effect of alien abundance on resource fluctuations.
May either accelerate or retard invasive spread)
A conceptual
model of alien
plant spread
(Higgins and
Richardson, 1996)
THREE PREDICTIVE MODELS OF PLANT SPREAD
a. Simple-demographic
b. Spatial-phenomenological
c. Spatial-mechanistic
a. Simple demographic models
These models aim to predict the future number of individuals in
a population. They make assumptions about the nature of
population growth, and the important demographic factors
influencing population growth. These are useful for predicting
the likelihood of establishment, extinction and population
density
a. Simple demographic models – different types
• Exponential growth model – most basic demographic
model. Assumes an exponential rate of population
growth. Time and population size are continuous
• Logistic model – assumes that environmental
resources are infinite. Time and population size are
continuous
• Logistic difference model (discrete model) – time and
population sizes are used as discrete variables (i.e.
not continuous, as in the exponential and logistic
models)
• Stochastic model – accounts for variability in the
behaviour of the population
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b. Spatial-phenomenological models
• Used when predicting the area occupied by the
invasive population.
• Assume relatively homogenous plant environment interactions which are determined
by empirically derived constants.
• They can forecast future events without making
any ecological assumptions.
• Useful if the ecological mechanisms involved
aren’t understood, and if certain that the past
can be used to predict the future. Disadvantage
is that ecological knowledge is not enhanced
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b. Spatial-phenomenological models – different types
• Regression model – most simple spatial model. Uses historical
records to quantify the relationship between area invaded and
time
• Geometric model – assumes that there are multiple introduction
foci, therefore a number of independent foci expand radially on a
large, homogenous, two-dimensional plane. Ignores population
demography and assumes no restrictions on population growth
• Markov model – uses matrix algebra to formulate discrete-time
and discrete-space models. Commonly used in forecasting
landscape change
c. Spatial-mechanistic models
These models are based on independent estimates of
ecological parameters
Different types of spatial-mechanistic models
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1. Reaction-diffusion model – assumes the population is
homogenous, grows exponentially and spreads out by random
diffusion into a uniform environment. Has been successful in
describing the range expansion of a number of animal species
and diseases. However, models can underestimate rates of
spread by an order of magnitude
Different types of spatial-mechanistic models cont.
2. Population dynamic meta-population model – metapopulations are systems of local populations that are
connected by dispersing individuals. Can be modelled as a
system of population growth models
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3. Individual-based cellular automata model – local
environmental conditions experienced by each individual are
important, so the spread of a species is modelled on an
individual-by-individual basis
SELECTING THE MOST SUITABLE MODEL
• Requires consideration of the ecology of the invasion. An
understanding of the processes that determine and constrain the
invasion is crucial.
• Simple demographic models: Only when it can be assumed that
the area invaded is related to population density, or when the
objective is to estimate the chances that an invasive plant
population will successfully establish.
• Spatial models: When the spatial component of the invasions
(i.e. area invaded) is of concern.
• Spatial-phenomenological models: When knowledge of the
invasion mechanism is limited, or when quantitative data
required for a mechanistic model is not available
STILL MORE MODELS!
• Habitat models: Identify those areas that are more prone to be
colonised. Useful to assess suitability of a habitat for
establishment and spread of invasive species, and so they can
help to improve management strategies directed to prevent
biological invasions (Zalba et al, 2000).
• Niche models: define ecological limitations in the dimensions in
which the model is developed. Whereas habitat models look at
suitability, niche models look at suitability and “unsuitability”.
Consequently, a species’ present geographic distribution can be
projected via ecological niche models into geographic dimensions
to predict where the species will or will not maintain populations
(Peterson and Vieglais, 2001).
MAPS
• Mapping should help identify gaps in our knowledge, reveal new
patterns, and could be useful in predicting invasions.
• Remote-sensing is often used to map spatial distributions of
alien plants and monitor their changes over time in an efficient
manner (Stow et al, 2000).
• The mapping of invasion-susceptible environments (after
application of a model to the area or species) and periodic visits
to those sites would be a cost-effective monitoring and early
detection strategy. The variable/s that should be mapped will
depend on the goals of the mapping effort.
CLIMATIC MAPPING
• Predicts potential distribution of organisms in new areas and
under future climates based on responses to climate in home
ranges (Baker et al, 2000).
• The process examines the climate in an organism’s home range
and compares it with the climate in the area being assessed for
potential colonisation, or compares the same area under
different climate change scenarios (Baker et al, 2000).
• Climatic mapping is useful in determining the maximum limits
for establishment.
read Benning et al. (2002)
CLIMATE CHANGE
• Relationship between global climate change and spread of
invasive species is unknown.
• Elements of global change include change in atmospheric
composition, greenhouse-gas driven climate change, increasing
nitrogen deposition and changing patterns of land use which
fragment habitats and alter disturbance regimes (Dukes and
Mooney, 1999).
• Definite effects of climate change are the increasing carbon
dioxide levels and increasing global temperatures.
• Changes in atmospheric concentrations of carbon dioxide and
subsequent climate change may facilitate biological invasions,
both directly and indirectly (Weltzin et al, 2003).
Figure 2. Conceptual model of direct and
indirect effects of elevated CO2 levels on
plant invasion (Weltzin et al, 2003).
DUKES & MOONEY HYPOTHESIS re climate change (1999)
• Most aspects of climate change to favour IAS, exacerbating the
impacts of invasions on ecosystems.
• Impacts include:
competitive effects, whereby an invading species reduces
resources available to other species, and
ecosystem effects, whereby an invader alters fundamental
properties of the ecosystem.
• New climate might not necessarily favour alien species, but the
rapid change would definitely favour alien species, which often
respond rapidly to disturbance and change.
MORE ON CLIMATE CHANGE
• Invasive animal species are more likely to be generalists than
specialists, and thus might be more successful than
indigenous species at adapting to new climates.
• Climate change could potentially favour IAS by creating more
favourable environmental conditions for them, e.g. increased
fire frequency (D’Antonio, 2000).
• Changes in the frequency, intensity, spatial pattern, or scale of
essential disturbance regimes through changes in climate
could encourage the replacement of indigenous species with
aliens.
MORE ON CLIMATE CHANGE cont.
• Species composition could potentially be detrimental to
ecosystem goods and services.
• Potential impacts include: shifts in relative abundance and
distribution of indigenous species, changes in species and
community richness, and even extinctions of indigenous
species.
• In the Gulf of Maine, climate change and sustained over-fishing
are acting together to favour introduced species (Harris and
Tyrrell, 2001).
THE WOOLLY ADELGID THREAT
• In the Pacific Northwest, where the current climate restricts
the alien balsam woolly adelgid (Adelges piceae) (a serious
pest of fir trees), to low and middle elevations.
• If higher elevations warm, the adelgid might be able to
reproduce and spread into higher elevations, where
subalpine fir (Abies lasiocarpa) is a major component of the
forests (Franklin et al, 1992).
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CARBON DIOXIDE
• Many invasive plants respond positively to elevated CO2 levels,
such as cheatgrass (Bromus tectorum) and kudzu (Pueraria
lobata) (Dukes and Mooney, 1999).
• When kudzu is grown under elevated CO2, it produces more and
longer stems and more biomass (Sasek and Strain, 1988).
• The response of kudzu shows that elevated CO2 could promote,
and may have already contributed to, the spread and
environmental impact of other alien plants including mesquite
(Dukes and Mooney, 1999).
CITIES AND CLIMATE CHANGE
• Many IAS found in cities originate in warmer areas
• Cities are “heat islands”, so the response of alien vegetation is
thought to be indicative of the response to global warming
(Sukopp and Wurzel, 2003).
• The percentage of heat-resistant plants among city vegetation is
high, often correlated to the temperatures of their home ranges.
• Most IAS in urban areas are confined to warmer sites, so low
temperatures may limit invasions. A high percentage of alien
spp. characteristises urban floras (Sukopp and Wurzel, 2003).
Chapter 1 Definitions
Chapter 2 History, globalisation and GMOs
Chapter 3 The human dimension
Chapter 4 Pathways of introduction
Chapter 5 Characteristics of invasive alien species
Chapter 6 The ecology of biological invasions
Chapter 7 Impacts of invasive alien species
Chapter 8 Invasive species management
Chapter 9 Predicting invasive spp. occurrence and spread
Next
Chapter 10 Ecological restoration
Chapter 11
Chapter 12
I hope that you found chapter 9 informative and that
you will enjoy chapter ten.