Why do Invasive Species Successfully Establish & Invade?

Transcription

1 Why do Invasive Species Successfully Establish & Invade?

2 Many are introduced, few become invasive

3 Hypotheses about why invaders succeed: 1. Invasive species have traits that favor establishment and spread 2. Invasive species are released from enemies 3. Invasive species exploit empty niches 4. Invasive species are favored by anthropogenic pressure on natives (disturbance)

4 Hypotheses about why invaders succeed: 1. Invasive species have traits that favor establishment and spread 2. Invasive species are released from enemies 3. Invasive species exploit empty niches 4. Invasive species are favored by anthropogenic pressure on natives (disturbance)

5 What traits favor invasive species?

6 Traits favoring invasive plants Seed production More seeds, more likely to be invasive Brassica tournefortii

7 Traits favoring invasive plants Seed production Rapid growth Faster growth, more likely to be invasive Polygonum cuspidatum

8 Traits favoring invasive plants Seed production Rapid growth Phenological plasticity Willis et al., 2010

9 Traits vary by invasion stage Stage Plant Traits Theoharides & Dukes, 2007

10 Problem: We ve found very few traits common to invasive species, and none of them are universal You ll explore this topic more in team exercise #2 next week

11 Hypotheses about why invaders succeed: 1. Invasive species have traits that favor establishment and spread 2. Invasive species are released from enemies 3. Invasive species exploit empty niches 4. Invasive species are favored by anthropogenic pressure on natives (disturbance)

12 Observation: Invasive plants perform better in their non-native range Non-native Range Native Range Mack et al., 2000

13 Enemy Release Hypothesis Release: fewer herbivores are eating me Advantage: non-native plants grow more leaves/roots/flowers and invasion succeeds

14 Enemy Release Hypothesis Release: fewer herbivores are eating me Advantage: non-native plants grow more leaves/roots/flowers and invasion succeeds Alternative: Biotic Resistance Resistance: new species are eating me and competing with me Disadvantage: non-native plants are less successful and invasion fails

15 Life of the plant

16 Specialists vs. Generalists

17 Specialists vs. Generalists

18 Enemy Release in Plants Study of 473 naturalized plants in the U.S. Mitchell & Power, 2003

19 Enemy Release in Plants Mitchell & Power, 2003

20 Enemy Release in Plants Noxiousness/Invasiveness: Proportion of states declared noxious/invasive Mitchell & Power, 2003

21 Enemy Release in Animals Study of 26 non-native species Torchin et al., 2003

22 Evolution of increased competitive ability (EICA) Genetic diversity creates opportunities for rapid phenotypic response

23 Optimal defense hypothesis Defense is costly for plant fitness Tradeoffs between growth and defense. Too little defense and you re eaten, too much defense and you can t compete.

24 Defense! Toxins (aka allelochemicals)

25 Defense! Toxins (aka allelochemicals)

26 Defense! Toxins (aka allelochemicals) Structural defense

27 Defense! Toxins (aka allelochemicals) Structural defense Tolerance Keep a reserve of resources to regrow what s been eaten

28 Evolution of increased competitive ability (EICA) Start with advantage due to enemy release Optimal defenses evolve in response to enemy release With sufficient genetic diversity, species can evolve rapidly to spend more resources growing and fewer resources defending

29 Species of the day: Cane toad (Bufo marinus) Native to South & Central America Introduced to Australia for biocontrol of beetles in sugar cane Secretes a toxin (bufotoxin) when threatened poisonous to most animals

30 Gradient of toad arrival history Phillips et al., 2004

31 Snakes that eat toads are poisoned Red-bellied black snake Green tree snake Phillips et al., 2004

32 Snake evolution in response to toads 1. Greater exposure leads to increased resistance to toad toxins Resistance

33 Snake evolution in response to toads 1. Greater exposure leads to increased resistance to toad toxins 2. Greater exposure leads to snakes with larger bodies, but smaller heads Change in body size Change in head size Less resistant to toxin

34

35 Purple loosestrife and specialist enemies G. pusilla leaf feeder L. salicaria invasive plant H. transversovittatus root feeder

36

37