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Biological Invasions

Biological Invasions. Peter B. McEvoy Insect Ecology Ent 420/520. Learning Objectives. Highlight the importance of invasions Pose and answer basic questions about invasions Critique approaches based on expert opinion Critique statistical approaches Critique mathematical approaches

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Biological Invasions

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  1. Biological Invasions Peter B. McEvoy Insect Ecology Ent 420/520

  2. Learning Objectives • Highlight the importance of invasions • Pose and answer basic questions about invasions • Critique approaches based on expert opinion • Critique statistical approaches • Critique mathematical approaches • Assess the current status and future prospects for a predictive theory of invasions

  3. Statistical Profile of an Invader(Sailer 1983, Niemelä & Mattson 1996) • Taxonomic composition • Geographic origins • Mode of entry • Economic status • Effectiveness of quarantine procedures

  4. Who Are the Invaders? • 66% of Invaders, 1383-2000 spp., Come From 3 Orders • Hymenoptera • Coleoptera • Homoptera Sailer 1983

  5. Where Do Insect Invaders Come From? 66.2% Western Palearctic (i.e. Europe) Sailer 1983

  6. How Many Invaders Become Pests? Foreign species make up only 2% of fauna, but 40% of pests 43% of beneficial spp. are accidentally introduced Over half of foreign species become pests Sailer 1983

  7. How Can Invasions Be Prevented?Effectiveness of Quarantine Procedures Number of Species

  8. Asymmetry in the Insect Exchange Between Continents Asymmetry characterizes most if not all biotic interchanges between biogeographic regions 300 spp Europe North America 34-44 spp Niemela and Mattson 1996

  9. Hypotheses of Vermeij (1991) to Explain Asymmetric Biotic Exchange. • Transport by trade and human dispersal. Numbers of invaders going in any direction are proportional to the size of conduits for their passage • Species pools as a source of colonists.Numbers of invaders reflect differences in the number of species available for dispersal from the donor environment • Ecological opportunities for immigrants.Numbers of successful invaders are determined by the wealth of ecological opportunities for them on their arrival • Intrinsic superiority of European species.Invaders from one donor environment are intrinsically competitively superior to those from other donor environment. “Hostile takeover” phenomenon.

  10. Forests of the World

  11. 1. Transport: Most Immigrants From NA to Europe Follow Their Hosts • Of the 44 NA insects invading Europe • 17 Homoptera • 15 Hymenoptera • 6 Lepidoptera • 4 Coleoptera • 1 Thysanoptera • 1 Diptera • most have followed their introduced NA host plants, except for 5 broadly polyphagous species.

  12. 2. Species Pools of Similar Size (100,000 spp): Some Phytophagous Species in NA and Europe

  13. NA  EU for Phytophagous taxaNiemela and Mattson 96

  14. Different Ecological Opportunities for Immigrants • Potential hosts(area, species richness, similarity to native hosts, parasite-host synchrony) • Enemy-free space(parasitoid species per host; Breeding bird densities) • Competition-free space (species packing) • Bioclimatic conditions (high to low latitude insect transfers)

  15. Top-Down Biotic Resistance to Invaders Carnivore Parasitoid Bird Herbivore Native NIS

  16. Bottom-Up Resistance to Invaders Consumer 1 Consumer 2 Resource

  17. Forest Cover: NA = 2x Europe % woodland cover 1910 % woodland cover 1990s % woodland in conifers 1990s % Cover Niemela and Mattson 1996

  18. Potential Hosts: European Aliens Adopt Close Relatives of European Hosts • Most common hosts of exotics are genera common in Europe: Prunus > Malus > Betula > Populus> Salix > Pinus > Quercus > Pyrus > Crataegus > Acer > Ulmus > Alnus > Picea) • Least common hosts of exotics are genera not naturally represented in Europe: Carya, Chamaecyparis, Robinia, Pseudotsuga, Thuja, and Tsuga) Niemela and Mattson 1996

  19. Host specificity of invaders “The majority of insects invading North American forests have, in fact, been rather diet specialized, contrary to expectation. For example, 68% of the European invaders are mono- or oligophagous.” Matson et al. 1994

  20. Host Availability • Similar hosts.Potential hosts abundant and closely related to ancestral hosts in both NA and Europe • More hosts in NA. NA has 2x species and genera because many shared genera went extinct in Europe during Pleistocene • More abundant and less fragmented in NA.NA tree abundance 2x Europe because Europe has higher human densities

  21. Intrinsic Superiority • Strong selection for aggressive competitive and colonizing ability (Pleistocene glaciation and extinction, settlement and fragmentation) • Adaptive traits • Phenotypic plasticity • Uniparental reproduction • High reproductive potential • Polyploidy • High dispersal potential • Protection from competitors and natural enemies • Stress tolerance mechanisms such as dormancy

  22. High to Low Latitude Transfers • Dormancy. Importance of entering and leaving dormancy at appropriate times • Latitudes.Owing to vast differences in latitudes of the deciduous forests of Europe (43-60o N) and North America (30-48o N) and importance of photoperiod as a cue • Asymmetry.Insects going Europe to NA better adapted for environmental synchrony than vice versa

  23. Necessary and sufficient conditions for invasion • Ability to find potential hosts in new environment • Ability to synchronize life cycles with conditions in new environment • Ability to increase population size when rare • Ability to colonize disturbed systems These conditions are more likely to be encountered by European insect traveling to NA than NA insect traveling to Europe based on ability of insect

  24. Biocontrol: An Exception to the “10s” Rule of Williamson

  25. Predicting Risk to Native Plants in Weed Biocontrol (Pemberton 2000) • Field host use of 117 organisms established for biological control of weeds from 1902- 1996 • Taxonomic groups: 112 insects, 3 fungi, 1 mite, and 1 nematode • Geographic areas: Hawaii, the continental USA, and the Caribbean

  26. Biocontrol As an Invasion Process • Target effects. How likely is control organism to establish, increase, spread, suppress target invader? • Nontarget effects. How likely is control organism to increase and spread out of control to colonize and harm native hosts? • Selected for success? BC agents presented with unlimited resources, enemy-free space, matching climatic conditions – and still majority of them fail to control target or use predicted nontargets.

  27. Operational Definitions • “Use” defined as introduced control organism completes its life cycle on non-target plant species. • “Closely related” defined as congeneric species of plants and species in closely related genera previously classified as the same genus. • “Co-occurring” defined as occurring together in the same state.

  28. Main Conclusions Risk is borne almost entirely by native plant species that are closely related (same genus or closely related genus) to target weeds • Taxonomically related hosts.15 spp bc insects use 41 native plant species • 36 of 41 natives are congeneric with target weeds • 4 others belong to two closely allied genera • Taxonomically unrelated hosts. Only 1 of 117 established biological control organisms uses native plants unrelated to the target weed.

  29. Elements of Safetyfor Protecting Native Plants • Selecting the right environment :select weed targets that have few or no native congeners in recipient environment • Selecting the right organism : introduce biological control organisms with suitably narrow diets

  30. Fisher-Skellam TheoryGrowth and Diffusion Equation • N = N(x,y,t) local population density organisms/area at time t and spatial coordinates x, y • D coefficient of diffusion • f(N) a function describing net population change

  31. Asymptotic Rate of Spread • For large time, the velocity (distance/time) VF for the advancing front approaches an asymptotic rate of spread, which depends on the intrinsic rate of increase  and the coefficient of diffusion D. • The radius of a species range should asymptotically increase linearly with time with slope (4D)

  32. Data requirements • Intrinsic rate of increase • Diffusion coefficient

  33. Rice Water WeevilAccelerating spread, two scales of movement

  34. Japanese Beetle Begins Slowly, Eventually Constant Rate of Spread

  35. Gypsy MothNon-constant velocity related to temporal variation in quarantine and spatial variation in temperature > 7o C Quarantine <7o C

  36. Small Cabbage White Butterfly Increasing number of generations

  37. Predicted and Observed Rates of Spread

  38. Summary • Retrospective studies of invasions yield a statistical profile of invader that may be useful for management(prediction and mitigation) • Usefulness of diffusion models for understanding observed patterns of spread and predicting invasions

  39. General observations after our paper critique • Clear, operational definitions • Statistical basis for inference • Control for opportunity for invasion • Pitfalls of univariate approach to multivariate problem. Assumes other things are equal and they seldom are. • Need for phylogenetically controlled comparisons. • Anthropocentric bias to data. Aliens account for 2% of our insects but 60% of our pests. • Avoid Tautology. European insects are more invasive because of their competitive superiority. • Argument by example leads to rebuttal by counter-example

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