Predicting occurrence & spread

1. Predicting occurrence & spread • 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).

2. Ricciardi & Rathmusen’s guidelines 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

3. Mack’s eight methods MACK (1996) ANALYSED 8 DIFFERENT METHODS • 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 • 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

4. Mack’s eight methods • 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

5. Mack’s eight methods • 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 • 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 closely-related congeners

6. Mack’s eight methods • Experimental sowings(no manipulation of the environment).Limitation: the factors that apparently restrict the range may operate infrequently • 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. • Mathematical models to predict the course of plant invasions

7. Models MODELS http://imagesearch.yahoo.co.kr/isurf/84/7448/14196/20025/0000415182.html http://www.motorcycledaily.com/28may03motoguzzi_evtouring.htm http://www.books-n-magazines.com/html/x_vogue.html http://pub.tv2.no/TV2/underholdning/bilder_ccr/article187917.ece?show=8 • 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!

8. Conceptual model 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)

9. Conceptual model flow-chart A conceptual model of alien plant spread (Higgins and Richardson, 1996)

10. Three predictive models THREE PREDICTIVE MODELS OF PLANT SPREAD • Simple-demographic • Spatial-phenomenological • Spatial-mechanistic • 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

11. Simple demographic models 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 http://users2.ev1.net/~jemhadar/images/maelstroms_eye/me237-natasha_henstridge_006.jpg

12. Spatial-phenomenological models 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 http://perso.wanadoo.fr/imagesdeparfums/indexfr.htm?http://perso.wanadoo.fr/imagesdeparfums/Campbell_Naomi/Mystery_image01.htm&2

13. Spatial-phenomenological model types 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

14. Spatial-mechanistic models c. Spatial-mechanistic models These models are based on independent estimates of ecological parameters Different types of spatial-mechanistic models • 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 http://www.geocities.com/FashionAvenue/Catwalk/4272/Dws036.jpg

15. Spatial-mechanistic models types Different types of spatial-mechanistic models cont. • Population dynamic meta-population model – meta-populations are systems of local populations that are connected by dispersing individuals. Can be modelled as a system of population growth models • 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 http://galleries.news24.com/2003/2003sport/15.asp

16. Selecting the best model 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

17. More models! 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).

18. Maps 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.

19. Climatic mapping 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)

20. Climate change 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).

21. Conceptual model of CO2 Figure 2. Conceptual model of direct and indirect effects of elevated CO2 levels on plant invasion (Weltzin et al, 2003).

22. Dukes & Mooney hypothesis 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.

23. More on climate 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.

24. More on climate change cont. 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).

25. Woolly adelgid threat 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). http://www.forestryimages.org/browse/detail.cfm?imgnum=0795074 http://www.chattoogariver.org/Articles/2002Su/HWAUpdate.htm

26. Carbon dioxide 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).

27. Cities and climate change 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).

28. Links to other chapters Next Chapter 1Definitions Chapter 2History, globalisation and GMOs Chapter 3The 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 Chapter 10 Ecological restoration Chapter 11 Chapter 12 I hope that you found chapter 9 informative and that you will enjoy chapter ten.