Invasion Ecology
Readings: text chapter 9
Part 1: predicting invasion success
What is an alien species?
• Species introduced to regions outside of their
historic (post-glacial) native range;
• Species are being transported to new locations at
up to 10,000 times greater rate than by natural
dispersal
• Aliens are also called:
• exotic species, non-indigenous species, nonnative species, introduced species, colonizing
species.
There is a general agreement now to ‘alien invasive species’,
meaning non-native species introduced to new areas where
they cause problems
A new debate focuses on whether we should introduce
endangered species from one location to another if the habitat in
the home range is the reason why the species is endangered
(e.g. butterflies). The process is called assisted migration.
Much of the issue has focused on helping species affected by
climate change (e.g. plants).
200
175
150
125
Hemimysis anomala
(2006) bloody red shrimp
100
No new alien since 2006
associated with ships,
even though ships
account for 55-70% of
invaders since 1959.
75
50
25
Year
2010
1990
1970
1950
1930
1910
1890
1870
1850
0
1830
Cumulative number of invasions
NIS in the Great Lakes
Ricciardi (2006) CJFAS
Pattern is very similar to other aquatic ecosystems
Fig. 9.1: San Francisco Bay
Mediterranean Sea
(cumulative number)
(non-cumulative number)
100
80
60
40
20
<1900
Shipping far less important in
other water bodies globally
1940
1980 >2000
canals
ships
canals and ships
aquaculture
Galil (2011) in Encyclopedia of
Biological Invasions
Studies on invaders have increased dramatically
since the 1980s for most species
Studies on Water hyacinth
(Eichhornia crassipes)
Zebra mussel (Dreissena
polymorpha)
100
100
80
80
60
60
40
40
20
20
Studies
0
1965
1970
1975
1980
1985
1990
1995
2000
2005
0
1965
Year
MacIsaac et al. (2011) in Fifty Years of Invasion Ecology
1970
1975
1980
1985
1990
1995
2000
2005
Scientific publications pertaining to Invaders
The invasion
literature has
exploded since
1990
Blue bars = 7
synonyms for
alien species
Red line =
Citations of
Charles Elton’s
book
Ricciardi & MacIsaac (2008)
Nature
Charles Elton’s (1958) Invasion Concepts
1. species-poor habitats are more vulnerable to
invasion than species-rich habitats due to lack
of biotic resistance (e.g. competition, predation,
parasitism);
2. islands sustain higher invasion rates and greater
impacts than do continents
•
•
based on idea that islands are biologically impoverished, and thus less
stable and more vulnerable to invasions
same idea became dominant in ecology (i.e. diversity begets stability)
in 1960s-1970s
3. habitats disturbed by man are more vulnerable
than less disturbed ones;
cover of Elton’s book, reprinted in 2000.
Historical View
What influences invasion success?
1) Species Characteristics
•
•
•
•
•
•
•
•
•
•
•
•
•
high fecundity
small body size
vegetative or asexual reproduction
high genetic diversity
high phenotypic plasticity
Evidence in support of
broad native range
these ideas is not always
abundant in native range
physiological tolerance
supportive, and sometimes
habitat generalist
contradictory
human commensal
loss of natural enemies
invasional meltdown
polyphagy
Historical View
2) Generalizations Regarding Habitat Invasibility
•
•
•
•
•
•
•
climatically matched
disturbed
low diversity
absence of predators
presence of vacant niches
low connectance of food web
nutrient rich (plants)
Alien Plants that Spread or Do not Spread
Rejmanek and Richardson (1996) Ecology
Analysis of spreading ability in introduced plants
• Analysis of 114 introduced
plants in North America
• looked at 11 attributes
• spreading associated with
invades elsewhere,
vegetative reproduction,
length of time fruit on plant
and perfect flowers
• non-spreaders were
associated with evergreens,
hybrids, native to the
continent or to temperate
Asia, need for cold exposure
to germinate
Rejmanek and Richardson (1996) Ecology
Invasive vs. Non-invasive fishes in the Great Lakes
• used a stage based
appoach to predict
success
• sought to explain
success at each
stage
Kolar & Lodge (2002) Science
• Successful invaders tended to have faster growth and could
tolerate wider variation in temperature and salinity
• Spreaders had slower growth but tolerate wide temperatures
Fire Ants
• Introduced to Mobile, Alabama last century from South
America and have spread across southern USA since
• Spread in USA seems to correlate with super colony
function (normally colonies aggress one another)
• Spread to Caribbean, Australia, New Zealand, Taiwan and
China, including Hong Kong and Macau from USA
Genetic assignment of thousands of individuals reveals that all but one
introduced population globally came from the USA rather than the original
source in South America (grey).
This shows a pattern of ‘stepping stone’ invasions, where South America
served as the original source, though the USA became the source for global
spread once it invaded there
This pattern of spread is consistent with a ‘propagule pressure’ hypothesis
since there is much more trade from the USA globally than from Argentina
More on propagule pressure later
Asunce et al. (2011), Science
• study used 66 nuclear
microsatellite markers
• examined 2144 colonies
of ants from 75 different
locations globally
• used genetics to
reconstruct the pathways
of invasion
Asunce et al. (2011), Science
Exotic Plants invade hot spots of native plant diversity
• at small scale (1 m2), invader diversity was inversely related to native
diversity in 4 prairies
• at the 1000m2 scale, the opposite was true. Invader richness was
positively correlated to native richness, soil nutrients (N, C) and foliar cover
Stohlgren et al. (1999) Ecological Monographs
California plant communities (Levine, 2000, Science)
• richer communities are more invaded even though
at small scales seed germination success of
invaders is low
• suggests local phenomena (competition) is
overwhelmed by ecological variation and
propagule pressure at larger scales resulting in a
positive relationship between NIS and native
species diversity
Marine ascidians (tunicates)
Stachowicz et al. (2006) Marine
Ecology Progress Series
•Survival of invaders was inversely related to native diversity.
• Space availability inversely related to native diversity.
•Colonization by invaders occurs when native are not recruiting
Facilitators Common
Facilitators Rare
• When resources (open space) are not limiting, biotic
resistance mechanisms cannot operate and NIS and native
diversity are positively correlated;
• as space become limiting, biotic resistance increases and
relationship becomes negative
• facilitators can offset the effect of biotic resistance by
providing habitat for NIS to colonize
Stachowicz et al. (2006) Marine Ecology Progress Series
Paradox of invasion: positive relationship between invader
and native diversity at large scales, but negative relationship at
small scales
• Extrinsic conditions differ
between point clusters, but
are the same within (e.g.
nutrient levels).
• Within a cluster, high native
diversity leaves few vacant
niches, so a negative
relationship exists for NIS
(small spatial scales).
• At larger scales or in
environments that promote
high native diversity, the
same factors may promote
high NIS diversity.
Shea and Chesson (2002) Trends in Ecology and Evolution
Are Islands more Invasible?
Number of NIS appears positively
related to number of native
species, and islands appear more
invaded than mainland
Lonsdale (1999) Ecology
Invader number is strongly
associated with native richness
(the rich get richer), habitat area,
whether it is a mainland or island,
and whether it is protected or not
Lonsdale (1999) Ecology
Visitors bring exotic
plants with them to
islands (open dots)
than on mainlands
(closed dots)
Number NIS plants increases with # of Visitors
and native plant species in South Africa
# NIS
plant
species
• # invader plant species directly correlated with visitor number
and native plant species diversity in S. Africa
• Suggests human are bringing seeds in with them (=propagule
pressure)
Assessing the role of Disturbance is not easy
due to confounding by other factors
Do invader plants colonize fields with cows because:
1) removal of competing native plants?
2) soil disruption/compaction?
3) manure fertilization?
4) seed introduction?
5) all of the above?
Habitat Characteristics favouring invasibility
Mark Davis has suggested that it is the ratio of supply and
demand of key resources that determines whether invaders can
colonize
Testing for Elton’s Ideas
1) Disturbance:
Meta-analysis (Lozon & MacIsaac 1997)
YES - 299 plant species: 86% - be careful since data could be biased
YES - 103 animal species: 12%
2) Native Species Diversity:
plants: YES: Fox & Fox 1986; Rejmanek 1996?; Tilman 1997
NO: Lonsdale 1999; Smith & Knapp 1999; Stohlgren et al. 1999
animals: YES: Case 1991; Stachowicz et al. 1999; Shurin 2000
NO: Hengeveld 1988; Moyle & Light 1996; Cohen & Carlton 1998
3) Islands vs. Mainlands:
YES: Plants (Lonsdale 1999)
Modern View
Stage-based methods to predict invasion success
• a number of groups have argued that more
progress would be made predicting invasions by
disentangling stages of the process than by
looking for species attributes or ecosystem
attributes to explain the entire process
• A stage based process looks at the different
factors that affect transitions between one stage
in the invasion process and the next
Model to Predict Invasions
Species Pool
A B C D E F G
Human
Introduction
Transport
(Dispersal) Filter
Physiological
Filter (+/-)
Biotic Filter (+/-)
Natural Colonization
E
G
Founding Alien Population
Alien Invasive Species (AIS) Colonization, Spread
and Management
Blackburn et al. (2011), Trends in Ecology & Evolution
Predicting Asian tiger mosquito Aedes albopictus
invasions using vectors and climate
Native region: red
Introduced: orange
Intercepted: yellow
Traffic to invaded areas was 2x
higher than to non-invaded
areas with similar climate
Climate matching of ports (top)
and airports (bottom)
Tatem et al. 2006, PNAS
Predicting invasions by Chinese mitten crab
(Eriocheir sinensis)
• native to South-East Asia
• Extensive invasion history in
Europe
• Catadramous lifecycle, undergoing
extensive migrations
• Occasionally found in Great Lakes
Predicting European occurrence from where it lives in Asia
• Data obtained for 457 mitten
crab reports in invaded
Europe and for 41 sites from
its native China
Mitten crab reports
Model used to predict European
distribution, and then it was
applied to predict in North America
Herborg et al.
(2007)
Conservation
Biology
• Model developed for Europe using Asian distribution data very accurately
(dark red) predicted the crab’s actual distribution (green)
• Very rarely predicted occurrence in areas where the crab is not found
• Very rare crab is found where it is predicted to be poor habitat
Relative risk based on ballast water proxy for propagule
pressure and environmental suitability
Risk group
High
Med High
Med Low
Low
NA
Port
Asian Model
Mean
SD
Ballast Volume
(tonnes x 103)
Relative
risk
Norfolk VA
98
8
365427
4.8
Baltimore MD
98
8
76160
1
Portland OR
67
34
65465
160.6
Houston TX
80
12
24836
60.9
New York NY
84
31
21019
51.6
Seattle WA
68
37
13266
32.6
Tampa FL
59
19
1021
2.5
Jacksonville FL
75
19
408
1
Oakland CA
33
44
21718
5.7
Boston MA
49
44
3792
1
Los Angeles /
Long Beach CA
0
0
30458
21.7
Miami FL
13
13
1402
1
San Diego CA
0
0
0
--
Herborg et al. (2007 Ecol Applic)
Predicted distribution of crab in North America
Apparent risk corresponds with amount of ballast dumped
(propagule pressure) and with environmental suitability;
red is high risk.
Herborg et al. (2007) Ecological Applications
Herborg et al. (2007 Ecol Applic)
Propagule Pressure
• number of introduction events
• number of propagules introduced per event
• condition of the propagules
Propagule pressure is a logical first step toward
predicting invasion risk
Colonization Pressure
• related to propagule pressure, but it refers to
the number of species introduced
Invasions related to Economy Size
The more you trade internationally, the more you expose
yourself to species from other countries that come in either
intentionally (stocked) or accidentally (ballast water)
Hulme (2009) Journal of Applied Ecology
Propagule Pressure Determines Invasion Risk
Probability
of
Establishment
Number of Propagules/Events
• Increased PP increases establishment probability by reducing
demographic stochasticity (Simberloff 2009)
• Increased number of release events increases establishment probability
by reducing environmental stochasticity (Simberloff 2009)
Reducing Propagule Pressure Reduces Risk
benefit
Probability
of
Establishment
Number of Propagules
• If we can reduce PP we can reduce risk by putting some of the
species present into a situation where they suffer from
demographic stochasticity
More Invasions Expected with more Invaders Introduced
Colonization Pressure
birds on islands
random data
Aliens
Established
Aliens Introduced (% of total available)
Lockwood et al. (2009) Diversity & Distributions
Native butterfly species distribution in Ecuador
Williamson and Gaston (2005) J. Animal Ecology
common
rare
Species Rank
A few species are super abundant (upper left), and many are
very, very rare (lower right). If I randomly collect 20
individuals, they will be dominated by individuals from the
common group, and perhaps there will be no rare species. If I
collect 2000 individuals, we expect some of the rare ones to
show up.
As I sample a community, I first
pick up common species, and
with further sampling start to
slowly add rarer species until the
curve saturates and all species
are represented
As I sample a community more
and more, the mean abundance
of each species collected
increases linearly
large inoculation
small
inoculation
Lockwood et al. (2009) Diversity & Distributions
Because colonization pressure
levels off, but mean propagule
pressure does not, the curve
flows upward
Propagule Pressure and Colonization Pressure
large release
moderate
release
small
release
Lockwood et al. (2009) Diversity & Distributions
Propagule Pressure and Colonization Pressure
Low demographic stochasticity
High demographic
stochasticity
• With high propagule release: a large number of AIS and high
propagule pressure for each (low demographic stochasticity).
• With low propagule release: few species present, and all are
present at low density and suffer from demographic problems
• 2 large benefits from reducing propagule release: fewer AIS,
lower densities of each
Relationship between Propagule
Pressure and Colonization Pressure
Data for ballast water and
sediments sampled from
ships coming into
Canada.
Ships are required to
flush at sea and take on
mid-ocean water, which
has fewer species and
lower abundances, thus
risk should be lower.
Briski et al. (2012), Proc. Roy. Soc. B
Invertebrates in ships’ ballast tanks on the Great Lakes
Pre-regulation
Post-regulation
18000
All Species
4000
Risky Species
14000
3000
Invertebrate
10000
Density
(Mean + S.E. 4000
individuals.m-3)
2000
2000
1000
0
0
Ballast water exchange reduces density and diversity of species capable of
colonizing the Great Lakes, and no new invasions have been reported
Bailey et al. (2011) Environmental Science and Technology
Determinants of Invasion Success
1) Hayes & Barry (2008, Biol. Invas.) reported
invasion success determined by:
• climate/habitat match
• history of invasiveness
• propagule pressure
2) Colautti et al. (2006, Biol. Invas.) reported
invasion success determined by:
• propagule pressure
• history of invasiveness
• physiological tolerance (fishes)
• disturbance