INTRODUCTORY
FACTS AND FIGURES ABOUT INVASIVES FROM COX
Lecture
1 Introduction to Invasion Biology
Lecture
2 Terms and Language
Lecture
3 - Accidental species introduction
Lecture
4 Intentional introductions
Lecture
5 Introduced parasites
Lecture
6 Characteristics of invasive species
Lecture
7 - Community and ecosystem - structure and function
Lecture
8 - Diffusion models
Lecture
9 Traveling Waves in Heterogeneous environments
Lecture
10 Stratified Diffusion
Lecture
11 - Application and testing of models: Types of data needed to construct
models
Lecture
12 - Application and testing of models: Choosing between models
Lecture
13 Exotics and Evolution
STATISTICS
ABOUT INTRODUCED SPECIES
Accidental
introductions how are they introduced?
Native
Invasives how can this occur? Primarily through human action
Agenda
for day:
(take
home: were not able or willing to make a go of it using the native biota,
were only able to last, for as little as they did before investors withdrew
support, based on the assistance of introduced species, particularly bees,
1.
Intentional for agriculture,
2.
Intentional for sport,
3.
Intentional for decorative,
4.
Intentional for land stability
5.
Accidental - fellow travelers
6.
Accidental - as a consequence of land changes
oExamples
of this include red maples (due to fire suppression leading to a decline
in the germination success of many oaks)
oMesquite
in the desert southwest (due to fire suppression and increased grazing
leading to a loss in many species of desert grassland plants and their
animal associates
2.
Be thinking about which species that you would like to begin working on
for the class it should not be one with which you are already familiar
or have worked on already
1)Current
attitude towards introduced species: WAR! INVASION!
a)Think
of some of the dire quotations about the current view of introduced species,
akin to war and terminology of conflict
a)-introduced:
species that come from one location and are brought to a new location
b)-exotic:
usually ditto a, but also a species from another location
c)alien:
ditto a
d)
nonnative: ditto a
e)-invasive:
a species that becomes abundant and influential invaders of a community
of native species
f)adventive: Located
outside habitat, though a reproductive population may not be established
g)-tramp: An
widespread ant species spread by human commerce with a specific syndrome
of life history characteristics: extreme polygyny, unicolonial or highly
polydomous nest structure, and colony reproduction by budding (sensu Passera
1994)
h)-commensal:
a species that lives with another
i)-pest:
any species that is not wanted by humans exclusively a human construct
j)-domesticate:
any species that we have domesticated and have around us by choice sometimes
used as a counterpoint to commensal or tramp
k)Native:
not introduced into that area by humans (the delineator that we could use
to determine a native vs. non-native plant.
a)Sign
up for two presentations, all of which will be done in pairs
b)Write
up a sheet that has the following format fill in the blanks
i)Hypothesis
Tested / General Goal / Theme(s) of Paper:
ii)Structure
of Paper:
iii)Comments:
iv)Questions
for Discussion:
c)Make
up a total of at least 5 questions for discussion that can be used to trigger
discussion, if it is flagging
d)You
should plan on giving a quick review of the paper (10-15 minutes or so)
and hopefully the discussion will either begin during your review or will
begin and grow after your presentation dont be upset if we start talking
about the paper before you finish all you had to present.You can work it
into the discussion as we go along, or as the discussion slows.
n)OR
2. approximately only 1 in 7 (14.3%) are successful enough to cause problems
to human endeavors - Simberloff 1996, Consequences vol. 2 online journal
ospecies
often escape from cultivation (Kudzu - Pueraria lobata) or from labs (African
Clawed Frog, Xenopus sp.)
ospecies
have moved around since humans began migrating and dispersing around the
globe
oa
variety of seeds, vermin, and other human associates have accompanied them
continually - most of the early movements did not move around large quantities
of species, typically only a few individuals.
oThe
large-scale movement of species via ships even predates the use of ballast
(originally dry ballast consisting of rocks, soil, or other stones, now
essentially unfiltered seawater) for shipping.
oEncrusting
species (barnacles, etc.) and boring species (isopods, barnacles, etc.)
have moved around even with the earliest of European explorers.
oBefore
1820, over 90% of the insect introductions were beetles - attesting to
the importance of dry ballast in the movement. These can also be traced
to ports in Southwest England and to their arrival points in Nova Scotia,
PEI, and St. Lawrence area. (later 1840-1860 leps became most common invaders,
with the increase in commerce in living plants)
oWhat
is the true distribution of species?
oPotentially,
many of the species that we currently think of as having a Holarctic distribution
may have originally been very limitedin their distribution (say to the
northern European seas).
oAn
impact of this realization is that many of us rely upon the distribution
of species to conduct biogeographic studies. as a consequence, many of
these studies may be flawed, possibly leading to erroneous conclusions
about phylogeny, if these characters are used in analyses.
oThese
errors could in turn lead to errors in studies of evolutionary or conservation
biology. If the latter is the case, we may make errors of judgment in the
design of conservation preserves or some similar applied question.
i)Main
threats:
competition and ecological replacement, land degradation, genetic hybridization,
importation of exotic illnesses (which well talk about next week) also
beneficial
aspects: could replace species that have been extirpated by human activity
(eg. Gemsbok and horses)
1.From
1948 1977, the US F&WS encouraged the introduction of exotic species
into N.A. for the purposes of game The federal program was stopped in
1970 and in 1977 Carter stopped the use of federal funds and resources
for exotic introductions (but what about fish stocking
?)
a.African
Gemsbok (Oryx gazella) was introduced into New Mexico and have successfully
competed with pronghorn (Antilocapra americana) and feral horses
(which are themselves reintroduced)
b.Reindeer
into Alaska competing with Caribou and destroying native tundra
c.Game
Ranching is popular in west, particularly Texas of axis, sika, and fallow
deer, blackbuck and nilgai antelope, Barbary sheep, Ostriches, emus, Eurasian
wild boar were all introduced into Texas in 1930s to 1950s because
of the extreme depletion of native game species by hunters
2.Fur
bearing animals have been introduced in many areas, particularly nutrias
these southern South American rodents devastate the local salt-marsh
vegetation through over reproduction and then over grazing and in the process,
competing with the native wintering waterfowl also serious predators
on bald cypress seedlings, and could lead to the elimination of this type
of vegetation in coastal Louisiana
3.Game
birds ring necked pheasant into NW US nest cuckolder in the endangered
prairie chicken nests
4.Sport
fish carp (huge despoiler of native vegetation and the local shore ecology),
brown trout outcompeting the native golden trout (Onchorhynchus aquabonita)
in Californias Kern River
C.
Domesticates
a)Biological
modes are a bit different quick review of life history of many species
i)Often
infect more than one species and as a consequence need normal host as well
as intermediate host(s)
ii)Often
spread by the intervention of one or more vectors
iii)Obligately
symbiotic (parasitic, parasitoidal, etc.)
iv)Often
have diseases go between humans and other animals in both directions
these are called Zoonotic illnesses (from Latin for animal disease
alteration [otic])
b)Similar
modes of spread and introduction are necessary (hurdle #1)
c)In
addition, before the parasite causing the epidemic or epizootic can become
established, and certainly before it can become integrated into the population
(following the scenario that we discussed at the beginning of the class),
the following are needed:
i)Vector
(if any)
ii)the
intermediate hosts (if any) are needed
iii)Proper
environmental conditions needed for all of the host(s) and vector(s)
d)Consequently,
the deck is stacked against parasites becoming established, much more so
than for free-living species
e)Have
several ecological types of parasites (decreasing ease of establishment
in novel areas)
i)Opportunistic
ii)Facultative
iii)Obligate
f)However,
the spread of these diseases is being increased with increasing shipping
and travel rates, particularly between areas that were not previously exposed
to shipping and travel
i)Of
particular importance for the spread of epidemics is adventure travel to
novel areas
a)Smallpox,
which is believed to have been introduced into the Roman Empire from Asia,
which wiped out ¼ of the Roman Empires population, and is hypothesized
to have been one of the factors which ended the Roman Empire
b)Bubonic
plague in the 1300s in Asia, which decimated the population in central
Asia, spread by the invading Mongols, who picked up the illness from Europe
(where it wiped out 1/3 of Europe)
c)AIDS
today
d)Malaria
- which is introduced into many areas where it was not previously.
e)Cholera
a disease introduced into and from many areas around the world e.g.,
Vibrio
cholerae which was introduced into Peru in 1991 from Asia introduced
in ballast water of ship, coincided with an algal bloom and then a red
tide out break (dinoflagellates, which are the intermediate hosts) as a
consequence of an El nino year sickened over 300,000 people and led to
the temporary ban on the selling of seafood exports from Peru, which is
a major component of their economy
a)Shrimp
viruses among the shrimp ranchers (or farmers)
b)American
Foul Brood disease (a spore forming bacterium, Bacillus larvae)
that may have been introduced into the US from elsewhere, probably Europe,
incubated here and then reintroduced into Europe and elsewhere
a)If
there are characteristics that can be used to predict the species that
may become established, we can predict better which species should receive
the majority of effort in control, when they are discovered in novel locations
b)Great
and obvious applied value and utility
c)The
characteristics that make a species an invader in one ecosystem may be
different from those that make or predispose a species to become an invader
in another ecosystem there may be a case-dependency on the species that
can be expected to be invasives
a)Abundance
in native land (Williamson & Fitter 1996: likely to become invasive,
probably single most important factor when comparing established invasives
and native species)
b)Widespread
distribution (often conflated with abundance)
c)Great
dispersal ability or migratory tendencies
d)Seed
production or great reproductive capability (often thought of as being
key Williamson & Fitter 96 disagree) being r-selected in general
e)Early
maturation
f)Large
body size (height, leaf size, and taller than wide)
g)Small
body size
h)When
an essential symbiont or key interactor is present elsewhere
i)Edge
species
j)Affinity
with humans (anthropophilic)
k)Capacity
for asexual reproduction
l)Number
of individuals being dispersed or released and the number of release events
m)Species
has a history of invading elsewhere
n)Close
relative has a history of invading similar habitat or just capable of invading
anywhere
3)The
above characteristics can be broken down into three general categories:
a)Those
that maximize or enable high reproduction
b)Those
that enable great ecological dispersal
c)Those
that enable species to be greatly ecologically flexible
Lecture
7 - Community and ecosystem - structure
and function
a.this
is not universally the case, there are entire ecosystems that are relatively
immune to invasion such as the vernal pond flora in central California,
which seem to be free of exotics
b.Similarly,
not all species have been equally successful in invading all areas and
that not all species are capable of invading a single given area despite
the fact that they have been introduced into those areas
c.given
that there are ecosystems that are differentially susceptible, species
that are differentially successful, and that the ranges in which those
species are able to invade are not limitless we should be able to create
some rules within which we should be able to predict which ecosystems may
be invaded, where species can disperse, and where they will be successful
d.We
can look at these questions in at least two ways: Empirically what have
their impacts been? And Theoretically, what would we expect from the introduction
of a novel player? The papers that well be looking at today generally
talk about the first question (empirical impacts of exotics), so lets
talk now about the theory end what can we expect?
a)Characteristics
of invaders (discussed
last week) we went through and came up with many characteristics of invaders
in different ecosystems and why they were thought to be so important.Remember
that we concluded that most of them could be lumped into three general
categories 1) those that enhanced the population growth rate, 2) those
that ensure that they will be dispersed, and 3) those that allowed them
to take advantage of the new place
b)Do
characteristics of invaders predict their impact?
i)Well,
numerically we have an ability to predict that very few of the species
introduced will have a major, ecosystem function-altering impact, because
of the tens rule
ii)However,
the tens rule is only an empirical observation, not a theoretical derivation
we dont really know why it is that only around 10% of the introduced
will become established and why only 10% will become integrated (invading)
into the community
iii)Can
get keystone exotics that dramatically restructure the ecosystem
into which they have been introduced what are the characteristics of
those that do dramatically alter the ecosystem functioning where they have
been introduced? (from Cox, ch 17, p. 240s)
(1)Ecological
distinctiveness of the exotic, relative to the preexisting natives appears
to be a key factor in the impact expressed
(2)Animals
of higher trophic levels often have a disproportionately large impact (such
as the piscivorous Nile Perch in Lake Victoria)
(3)Detritivores
tend to have minimal impact on the ecosystem
c)Are
there characteristics of resistant ecosystems? where would we
expect to be immune to introduced species?
i)Related
questions: are communities tightly constructed and related to each other
homeostatically
(as Cox says meaning that there is some sort of a feedback loop tying
together the population sizes of each species in the community) or are
they loose assemblages of individual species that have similar ecological
requirements? In other words, are they open or closed?
ii)The
first view is the equilibrial hypothesis of community structure
there are clear assembly rules that bind together the construction
of communities, most of which lie in the environmental conditions in which
they occur.If we know the ecosystem ahead of time, we could elegantly predict
what species will arise there.
(1)Species
are tied together based on their interactions (mutualisms, competitions,
predation, etc.)
(2)Based
on the intricate relationships among the species, we should expect that
these types of communities are closed to invaders and should have lower
invasion rates
(3)Therefore,
the main time in which these communities would become invaded would be
when they are disturbed or the environmental conditions are made to change
for some reason
(4)This
viewpoint also believes that changes in community structure are
unnatural
and usually a consequence of those changes the land-use managers who
attempt to espouse consistency in preserving a given community implicitly
adhere to this view of communities
iii)Second
view is the nonequilibrial hypothesis for open communities
(1)consequently,
the communities are easily invaded and those species that find the appropriate
environmental conditions (including the absence of predators and prey)
will be able to invade
(2)under
this viewpoint, the constancy that we sometimes witness is merely because
the species do not accurately track the environment which is actually continually
changing
(3)this
viewpoint views that change is inevitable and a natural part of the ecosystem
iv)experimentally
choosing between these two viewpoints is not easy, as all communities
are invasible to some degree similarly, it seems that disturbing
all ecosystems will lead to an increase in the number of invasive species
arriving and taking over
v)A
similar debate about the relationship between community characteristics
and invisibility is the role of enhanced biodiversity in preventing invasion.
(1)This
will be the focus of the Wiser et al. paper that well discuss today.
(2)Wont
talk longer about this
d)When
will these invasions happen and at what rate?
i)Frequently,
exotics have a time lag between their introduction and their explosion
WHY?
(1)often
this is correlated with the occurrence of a disturbance or perturbation
or the introduction of an exotic species
(2)Possibly
this is essential for the building up of the species to a population size
that is large enough to be explosive
(3)Could
be happening because of some ecological limitation (need to adapt to the
local ecosystem?) or because of some genetic limitation slowing them (bottlenecks
and hybridization with local species)
Implied
in this discussion is that we are not going to be able to model the movement
exactly. Also,there is therefore no universally agreed upon final point
at which a model is finished or is even adequate - they are mostly heuristic
devices for elucidating the essence of why and how species move.
·recognizes
that there are temporal fluctuations in population growth rates due to
clumping of birth and death events (discrete growth) or due to density
dependence within our population (logistic growth)
·essentially
only a modification of the diffusion model, with the assumption of uniformity
in the environment being change
·Recognize
both short and long-distance dispersal modes available to the animals
·Changes
the assumption of uniform and random walks
We'll
talk today about the base version of these movement models - the Diffusion
model.
2.
No predators or parasites or other factors limiting or affecting their
growth and movement
3.
no abiotic environmental factors (wind, storms, etc.)
4.
no density dependent factors are at work either (population is growing
exponentially)
5.
random walk - no directionality in movement - no obstructions hindering
reverse movement no influence of the movement of one species on another
6.
equal survival probabilities and equal death probabilities
7.
No difference in the Diffusion rate (rate of individual movement)
8.
(For MRR studies we also include: that the recapture rate is constant and
representational of the population as a whole
Base
equation of the model:
Time
lags leading to pulses in the distribution of species (more later in the
traveling wave model discussion.)
Jump
dispersal - when sudden long-distance (amount depends on scale) dispersal
occurs -- possibly due to the movement of propagules (seeds, spores, planktonic
forms, presence in ballast water, other human movement, etc.)
·Need
to correct something that I said incorrectly last time about waves of spread
·I
had erroneously said that you could get a series of waves under the base
diffusion model you would not, you would only get a single wave front
that increases behind the wave front and then stabilizes at the carrying
capacity (since we are using the logistic growth model)
·The
phenomenon that I mentioned last time (with the species consuming all the
resources behind the wave front and then making the environment uninhabitable
will be relevant to our discussion today. More on that in a bit.
·The
Environment will be thought of as a linear environment, with some patches
being favorable, and others disfavorable
·Individuals
will try to get out of the bad patches quicker than the good patches and
will do better in the good patches than the bad
·This
could also be true in a 2-D environment, where the patches change regularly
outward in the form of a bulls-eye
·Because
the environment is non-uniform, we have to have two sets of constants that
will be included into the base Fisherian diffusion model (1 will be for
the favorable environment and 2 for the disfavorable environment)
·l1
and l2 are the lengths of each patch == l1 and l2 are different but unchanging
·epsilon1
and epsilon2 are the intrinsic instanteous growth rate of the population
in each patch == epsilon1 is > epsilon2; epsilon 2 may be negative, which
will be relevant below
·d1
and d2 are the diffusion coefficients in each patch == d1 < d2
·If
favorable patches are greatly separated from each other (l1<<l2),
then the population will decline locally until it goes locally extinct
(fig. 4.2a)
·If
favorable patches are relatively clumped together (l1>>l2), then we get
our traveling wave, with a steady increase of the size of the general area
that is occupied. (fig 4.2b)
·When
would the traveling periodic wave be obtained? When will the invasion be
successful? (section 4.3) (see Fig. 4.3)
·E2
(the proportion of the intrinsic growth rate of the unfavorable to favorable
patch; epsilon2/epsilon1)
·D2
(the proportion of the diffusion coefficient [dispersal speed] of the unfavorable
to favorable patches; d2 / d1)
·When
the threshold E*2 value is exceeded (E2 > E*2), the traveling periodic
wave will be obtained
·E*2
= -(tan L1 / 2)squared / D2
·When
the threshold D*2 value is not exceeded (D2 < D*2), the traveling periodic
wave will be obtained
·L*2
= 2(tan L1 / 2) / -E2
·When
the threshold L*2 value is not exceeded (L2 < L*2), the traveling periodic
wave will be obtained
·D*2
= 2(tan L1 / 2)squared / -E2
·What
speed will this wave be spread, on average? (assuming constant D and d1=d2)
·If
there is no heterogeneity, it spreads only as a consequence of epsilon
and D; v= 0 in fig 4.4c
·If
the environment is exactly half and half (good vs. bad habitat), the wave
spread is roughly one half the rate if there were no heterogeneity (v =
1 in fig 4.4c)
·If
the environment is largely unfavorable, there will be times that the population
will not become established, let alone spread (v is large, = 4 in fig.
4.4c)
·Patch
size is of utmost importance not just an absolute patch size, but the
relative sizes of the good versus bad patches is key as is the relative
sizes of the bad patches relative to the dispersal abilities of the organism
(not stated by S&K, but should be emphasized)
·This
is also the point at which we introduce the idea that I had prematurely
introduced last week about the patches behind the front expanding into
optimal, all l1 habitat initially, being overexploited, and made to be
incapable of supporting the species
·This
would also produce the traveling wave front, but would do so only by slowing
down the waves behind the frontal one with the disfavorable habitat
·The
front wave would expand as though there was not unfavorable habitat
·The
secondary waves would be slowed by the recovery time (epsilon) of the resources
·We
could do one of two things with this mixed bag of patch sizes
·A.
we could calculate the spread of the species in each patch and then add
them all together
·B.
we could calculate the mean values of l1 and l2 and incorporate the sample
variance into the equation this latter one is the preferred route and
is akin to incorporating environmental stochasticity into the base exponential
and logistic population growth models.
·We
again have two possible outcomes in this model
·A.
local extinction (like fig 4.2a in periodic traveling waves)
·B.
irregular expansion of the propagating wavefront (like fig 4.5)
·Here
the wavefront expands irregularly and as a consequence of the relative
widths of the good and bad patch widths
·Also
it seems that the degree of sample variance does not play a huge role,
based on simulations the average spread of the population through time
seems to remain very constant, irrespective of the degree of spread irregularity
the average spread is very similar to that of the traveling periodic
wave
·Therefore: the
spread of the irregular traveling wave can be pretty accurately approximated
with the simple periodic traveling wave
·habitat
fragmentation and the movement of species through that environment
·A
reflecting versus absorbing barrier
·Edge
effects and their impact on the spread of species
·The
SLOSS debate
2.Discussion
of movement types range-versus-time curves
3.Scattered
colony expansion model
4.Coalescing
Colony Model
Premise:
review the types of models that have been used to model the spread of invasive
species
1.
Diffusion with random walk
2.
Diffusion in a heterogeneous environment
3.
Stratified Diffusion
·some
have said that the difficulty in modeling and the inability to generalize
any local model to more global uses may be the reason why people think
that invasions cannot be easily predicted using mathematical models
·similarly
the question of which model to use is relatively opaque - how to solve
this?
1.
autecological attributes -
·the
ecological or natural history characteristics of species that may lead
them to become invasives (e.g., nitrogen-fixing, short juvenile periods,
large dispersal phases, and others from Kolar & Lodge)
·this
is applicable to both the novel and the original habitats in which the
alien originated
·primarily
boiled down to the resource availability and disturbance regime
·many
scientists say (as we've heard already) that no invasion happens without
a disturbance, since humans have accelerated the disturbance regime so
appreciably, we are responsible for much of the current invasion rate
·environmental
quality influences so strongly the reproductive rates of the invasive species,
·often
these come about synergistically, such that the reproductive success of
the invasive is not solely determined by additive processes
·demographic
stochasticity,
·dispersal
patterns,
·age
or sex-specific mortality patterns,
Predictive
models of plant spread - Three general types:
A.
simple-demographic
B.
Spatial-phenomenological
C.
Spatial-mechanistic
a.
Exponential
growth model
b.
Logistic
growth model
c.
Discrete
models (a.k.a, Logistic -difference models) - analogous to the logistic
growth model, but time and population sizes are used as discrete variables,
e.g., not continuous individuals as in the exponential and logistic base
models - continuous models are more realistic and better developed than
discrete models
2.
Spatial
- phenomenological models are most interested in predicting the area
of the environment that is occupied by the invasive species, based not
on the ecological mechanisms that may be used to predict the spread.Instead
they assume that the organism-environment interactions are relatively homogenous
and determined by empirically derived constants
a.
Regression
models -use historical spread data to quantify the relationship between
area invaded and time - attempts to fit the area occupied already to logistic
curves using a regression - recognize that the spread of species progressively
slows as more of the environment is occupied - often used to infer backwards
where and when a species was introduced into the local environment
b.
Geometrical
models - assumes that there are multiple introduction foci - uses simple
exponential growth and ignores demographic stochasticity
c.
Markov
models- similar to above but use matrix algebra to capture more of
the space and time variables - commonly used in forecasting landscape change
impacts - a summed variable at some time t+1 in the future that is occupied
by the invasive - incorporates differential birth, death, and population
change rates in each landscape form - assumes that history has no effect
and that only the current ecology is important and that transition probabilities
are constant through time - have been used in the past to predict the spread
of root disease epidemics - involve no ecological mechanism, so it may
be useful if it is impossible to predict the future but cannot muster much
background information on the species, but have a great history of the
land use and changes
a.
Reaction-diffusion
models (what we have spent the last three weeks studying)
§assumes
that the population size increases and spreads out evenly locally and according
to a normal distribution (greatest in the center and follows a normal distribution
curve
§these
models are pretty robust to violations of many assumptions and have successfullypredicted
the spread of a great many animal species
§this
is often because of the strongly erratic and leptokurtotic dispersal distances
in plants due to wind and animal dispersal mechanisms
§predict
that the square root of the area should be a linear increase
b.
Metapopulation
models
§metapopulations
are systems of local populations that are connected by dispersing individuals
§can
be modeled as a system o population growth models
§if
we make an analogy between the local focus of the invasion with the local
population and model the population growth explicitly in the local environment,
we can very accurately predict the spread of species
§have
the problem of introducing a scaling artifact into the model when the local
patches are sufficiently dissimilar to not allow us to make homogenizing
assumptions.
c.
Individual-based
cellular automata models
§used
then metapopulation assumptions of habitat homogeneity and clean separation
between the component patches does not apply, say when the species do not
have local patches or flow evenly one "population" into another
§here,
the local environmental conditions experienced by each individual are important
and we therefore need to model the spread of a species on an individual
by individual basis
§assumes
that there are a discrete array of cells that can each take on a number
of states that will impact on the spread of the species
§incorporates
the environmental stochasticity and heterogeneity into them
§not
commonly used, even though they have obvious utility, most likely because
of the huge amount of background initial ecological assumptions necessary
to create the model