Invasive species

Disturbance* and invasion

- commonly accepted statement– Disturbance facilitates invasions Elton (1958) – noticed and suggested that the majority of non-native species (invasive) are found in human-disturbed areas

- More research – relationship between alien species ecosystem disturbance is more complex and complicate

* Each relatively discrete event that disturbs ecosystem, community or population, and change resources, habitat availability or physical characteristics of environment

- The fact is, regardless of level (population-ecosystem), disturbance cause ecological change that „open” the space or new possibilities in the community

- Marchetti et al. (2004) – alien fish species distribution pattern – is there a factor in the environment that enhance invasion?

- Many examples of alien species unsuccessful establishment caused by changes and disturbance in the system

nativ

e al

ien

- The more river drainage changed, the higher number of alien fish species

- However, not all alien fish species react the same onto changes and disturbance in the system

- ubiquitous changes in the environment (urbanisation, water bodies regulation, agriculture….) influence on alien species establishment success

- Generally accepted statement about disturbance enhancing invasions

is not general!

- There is no sense in discussing the disturbance as enhancer or retarder

of invasion – each species should be perceived separately (Higgins and

Richardson, 1998)

- Always guarding in mind 2 principles:

1. Disturbance gives chance to both native and alien species

2. If disturbance really increase the invasivness of an alien

species, there must be constant source of propagules

Agriculture and invasions

Puerto Rico example

- deforestation, population growth

– agriculture growth – changes in

the environment

- urbanisation – agriculture decline

- ex-agriculture areas reforestation

– domination of non-native trees.

Urbanisation and invasions

- Similar influence onto aliens as agriculture

- Alien species richness grow with the level of urbanisation, positive correlation with human population size – specially plant species (gardens, parks….)

- Urban areas – disturbances that create new conditions in the habitat (fertilisers, pesticides, irrigations….) - Resulting changes enhance alien species establishment + frequently continuous deliberate (& accidental) introduction of propagules in high numbers - Hard to distinguish which of these factors is crucial for alien species establishment

Biotic disturbance

- Alien species is by itself biotic disturbance in the environment or it is a factor that causes a change

- Mack i D’Antonio (1998) – sci. papers (58) analyses –prove that alien species

cause ecological changes

- Cover whole world, plants, fauna, and soil

- Based on their analyses, alien species effects could be:

1. Ones that change physical or biological aspects

2. Ones that change species reaction onto disturbance

1. Ones that change physical or biological aspects

Acacia mearnsii – invasive riparian species in South Africa (from Australia)

- River banks erosion

- Disturbance caused rapid colonisation of bare banks by alien plant species

Alien species are by themselves disturbance - Frequently refers to grazers (goats, sheep) or diggers - rooters (wild boars) - Grazers – change the cover – possible changes in plant species composition and fire cycles - Rooters

Mechanism – rooting – soil temperature changes, increased the availability of soil nutrients - Increased the abundance and diversity of annual species, both native and non-native, with a bias toward non-native annual grasses

Kotanen (1997)

Sus scrofa – in California (grassland) from Europe – changes in grassland and scrub communities – overturning soil and digging up roots

2. Ones that change species reaction onto disturbance

Global climate change and alien species - Global worming – green house gases

- Mainly separated studies of climate change and alien invasions - “overlap” climate change and alien invasions

Stachowicz et al. (2002) - sea squirts study – native and 3 alien species – sea temp rise – earlier reproduction of aliens - total annual recruitment of aliens positively correlated with sea temp negatively with native

- New England’s natives could be replaced with aliens due to temp rise

Conclusions:

- Environmental disturbances could be strongly connected with invasions,

but it is not easy a priori predict those connections

- A few existing evidences that suggest alien species successful invasion

after disturbance in the environment

Necessity of further research that will:

- Include disturbed habitats, still without aliens

- Use data on unsuccessful invasions in disturbed environment

- Include different alien species, unsuccessful ones, as well as those that could

profit from disturbance

- Include studies of all kind of disturbances within local ecological networks

Establishment Success: The Influence of Biotic Interactions

- conceptual paradigm within invasion ecology is the idea of biological resistance (Elton 1958; Simberloff 1986). - Paradigm suggests that abundant native’s population can stop establishment of aliens (disable them to reach the resources) – The most studied mechanism of invasion resistance includes competitive exclusion – two species can’t share the same niche (eg. Food source), one species will (sooner or later) „lose the battle” and disappear (Hutchinson 1959)

- But for (un)sucesfull alien species establishment other negative interactions should be

considered: predation, parasitism, mutualism……

- Frequently only by its growth (plant) the species will change local environment, eg.

Making shade, changing the substrate….and exactly that will help other species to

„flourish”

Native species, and previously established aliens, can either inhibit or facilitate the successful establishment of a newly arriving non-native species. The biotic interactions involved in each case include both positive and negative associations.

What stops aliens to become successful invaders and establish populations?

- One or more factors (competition, predation, parasitism, absence of

mutualist)

- Combination and interaction of biotic and abiotic factors

- Numerous obstacles – but still number of aliens (invasives) is constantly

growing and it is hard to conclude what help the system to resist the invasion

Davis et al. (2000) Each biological system can break under invasion, some faster, some slower Levine et al. (2004) Real biological resistance is possible only during the introduction stage

Modeling the Geographical Spread of Invasive Species - When stable population is established (positive population growth) it can continue to spread - Frequently aliens are noticed only when their population is big enough to make some impact

Spread incorporates elements from the transport and establishment stages. Dark circles represent high density populations and lighter areas represent lower densities. The alien can spread out from an initial establishment site in a diffusive way (solid lines from the established population) that leads to lower initial densities at the leading edge. The alien can also spread to new distant sites without colonizing the in-between area (dashed lines). Such jump dispersal might occur because of dispersal vectors such as wind, water, or organisms that eat or carry the non-native. It might also occur via human vectors operating within the non-native range.

- Spreading includes all stages that species passed in the beginning after entering the new area = recapitulation of the whole invasive cycle

Estimation rate of geographical spreading enables:

(i) Prediction which alien sp. will spread fast, and which will not

(ii) Establishing species life history traits or habitat requirements that are

essential for the fast spreading

(iii) Discovering priority areas that require special control

(iv) Targeted management, stopping the spread or slowing it down in the most

efficient way

Why modelling? - Predicting the spread, possibility to manage species more successfully, prediction of the

system’s future Good model – good input data, good knowledge on modelling

Figure 3. A–C. Habitat suitability models (HSM) based on altitude, slope, mean annual air temperature and land use (CLC 2000) for native A. astacus (A), native A. torrentium (B) and alien P. leniusculus (C) with their distribution of existing and extinct populations.

Ecological influence of invasive sp. onto native sp.

- Obvious and measurable when alien sp. passes all of the invasive stages

Influence onto genetic structure

- One of the most dangerous – disturbance of genetic integrity of native sp.

- Frequently hard to prove, request special knowledge (molecular methods), hard to

obtain material for analyses

- It is defined as a change in the native sp. gene pool, most frequently happens

through hybridisation (gene flow between 2 sp.) or introgression (gene flow

between the hybrids and/or hybrids and parental sp.)

- Fertile hybrids – could be more successful than parents (better fitness) and

frequently mate with invasive parent sp. (introgression) – native sp. gene pool is

changing + less chance to mate

Example: Anas platyrhynchos (wild duck) and endemic sister species from the same genus - Anas platyrhynchos - wide distribution (northern hemisphere) deliberately introduced into many other parts of the world (food, game sp.), including New Zealand, Hawaii, and Australia - endemic sp. - New Zeland grey duck (A. superciliosa superciliosa), Australian black duck (A. superciliosa rogersi) & Hawaiian duck (A. wyvillana)

- endemic sp. mates with alien – F1 hybrids mate with parental sp., as there are more individuals of alien sp (Anas platyrhynchos), less chance to mate with native parent – consequences – native sp. reproduction drops + “infusion” of alien genes – Will the native species survive as a separate species

Individual impacts

- Invasive sp. impacts the native sp. fitness - possible to measure – changes in morphology, behaviour or demographic (vital) characteristics (somatic growth, reproduction, survival) as a reply onto alien (invasive) sp. presence

S. foliosa S. alterniflora

majority of studies at the population level (easy to measure population numbers, distribution, and age structure…)

- Easy to observe impacts onto reproduction, survival and population growth – if trend is negative, highly probable that invasive sp. will push out native sp.

Population impacts

- Negative impact onto one population of one species will frequently impact the whole community – possible mass extinctions Example Nile perch – piscivorous species (Lates niloticus) introduced into Victoria Lake (1950) + other omnivorous fish sp. – mass extinction of native cichlids (from 400 sp, 200 extinct) -After introduction – drop in native cichlids abundance (competition & predation from aliens) -1978 perch < 1% annual catch– native cichlids 92% annual catch -1987 perch 97% annual catch– native cichlids zilch

Community impacts

- normally feed on grass and shrubs

- “Learn” to stand on their hind legs to reach foliage on the endemic native shrubs

- Result simplified vegetation structure, high amounts of open bare ground,

absence of several endemic - effect “cascades” up the trophic web and virtually

eliminates habitat for ground nesting birds

Example wild sheep (Santa Cruz Island, California)

(Van Vuren & Coblentz 1987)

Ecological influence of invasive sp. onto native sp.

Influence onto genetic structure

Individual impacts

Population impacts

Community impacts

Ecosystem impacts

- Changes in population sizes, individual behaviour, or community structure can alter both the flow of materials through an ecosystem and the disturbance regime that is typical of a native ecosystem

Example Tamarix spp. (native in Europe & Asia)

– invasive in S-W USA – extracts underground

water, rise in soil salinity – pronounced

droughts and salinity in riparian belt –

consequence – drop in native plants numbers,

changes in insects and birds communities

Global impacts

- Many examples of species extinctions (losses in species richness), but in some areas

biodiversity gains (thanks to alien sp introductions)

- Gains and losses are not equally distributed among different groups – species that

co-exist with humans profit from human’s influence onto environment and have

higher chances to be transported to a new habitat, and a higher chance to survive

- On the other side endemic species, not adapted to human’s impacts onto habitats

or impacts from aliens (competitors) will probably disappear

- Polarisation: WINNERS (smaller number, wide distribution) – LOSERS (numerous,

endemic) – homogenisation of flora and fauna

Perception and recognition of impact

- up till this point impacts on different levels of biological organisation were shown

Two graphical models that show the span of ecological, historical and social features that must be included into alien (invasive) sp impact analyses

1. How scientific and social (economic) communities’ perception influence onto analyses of aliens impacts?

Perception – scientific detection and social bias - Frequently limited and conditioned by human’s criteria (economy, aesthetics, ecological function, human health) and subjected to changes (according to „fashion”)

During perception and recognition of invasive species impact (from scientific or social aspect) take into consideration both ecological interactions, invasive species features, historical perspective as well as habitat characteristics

Ecosystem disturbances…

Life history traits, physiology, evolutionary history…

Competition, parasitism, predation, mutualism

Impact through historical events (transport vector, number of propagule…)

2. How to measure invasive sp. impacts?

To measure impacts on different levels (from gene to community) a common currency is

needed (economical, ecological….)

Question: - How to establish impact degree big enough to be measurable?

- How to know if impact is positive or negative?

A matter of perception

Biocontrol – introduction of alien species for controlling other alien species

Esthetical, medical, cultural, economical reasons for introduction (as long as they don’t do any damage and are beneficial, side effect is biodiversity gain

“Fashions” are changing or something that had positive (neutral) impact, could become harmful (negative)

Gemma gemma

Nutricola spp.

Carcinus maenas

(native)

(alien) (alien)

50 y. no influence

Example: Gemma gemma - Nutricola spp. - Carcinus maenas

+ C. maens – Gemma gemma became invasive

Economic currency - Logical choice, applicable everywhere - Pimentel et al. (2000) – estimated that USA spend 137 billions $/ year for fighting invasive sp. (all damages, removals, prevention…..)

Ecological currency Parker’s formula – enables comparisons of alien species impacts between different areas + good tool for identification of basic components of their impacts

I – impact R – area (m2) occupied by alien sp. A – average density of alien sp. / m2 E – alien sp. effect (per unit or alien sp. biomass)

I = R ∗ A ∗ E

To spot the impact & its strength - complex

The more scientific data and results – better input sets for meta analyses – better conclusions about invasions and invasive sp management

Evolution of invaders

Invasive model: transport - introduction - establishment- spreading - Introduced population could be big or small, it could be introduced by transport vector once or many times

- Genetic diversity of introduced population depends on number of introduced propagules, frequency (repetitive introduction), population growth rate

- Genetic changes that happen during the introduction have influence onto alien species establishment, spreading speed, level of impact onto native species, as well as on probability of its future evolution (adaptation) in the new environment (new abiotic and biotic factors)

- Evolutionary genetics of invasive species relatively poorly studied, could explain invasive mechanisms

- Recent research indicate that invasive success of a species depends more on their ability to endure natural selection than on their physiological tolerance and plasticity

- Genetic architecture of a species is important in selection and it enables evolutionary adaptation and possible speciation

Fisher promoted the theory that evolution is driven primarily by natural selection, mostly through its effect on additive genetic variation Wright thought that changes in allele frequencies associated with population bottlenecks provided a critical mechanism for evolutionary change + founder effect reduce genetic diversity

What is the connection between above mentioned and invasions, and how invasive species „fight with those two theories?

(i) How frequently genetic diversity „fall” during the establishing stage?

(ii) Is it the low genetic diversity in the introduced population limiting factor for establishment and growth of alien species population?

(iii) Is there enough genetic variability left after the founding event to allow key phenotypic traits to evolve that allow the population to spread and perhaps cause ecological impact?

How genetic structure changes in the introduced population?

By definition, alien sp population is established by a certain number of individuals that were transported from the original area and released into the new one

a certain number of individuals, normally, carries a part of genetic diversity (from the whole allele set) of original population

Each alien population carries a small part of rare alleles of original population

The level of genetic erosion in this population bottleneck depends on propagule numbers, source of propagules and frequency of transport vector (new arrival of propagules)

Example Baker & Moeed (1987) – genetic diversity comparisons between populations of alien Acridotheres tristis ( New Zealand, South Africa, Hawaii, Australia & Fiji) and population of native Acridotheres tristis (S-E Asia)

- 39 loci, average heterozygosity (HE) , number of alleles/locus (A), % of polymorphic loci (P) between populations - average heterozygosity & % polymorphic loci lower in alien populations - number of alleles/locus smaller – all lost alleles are the ones that are rare in the original populations

Baker & Moeed (1987)

1. Genetic similarity between native-alien populations

2. Genetic similarity between alien populations – significant differences (In some cases even higher than between already described species) - Recorded differences (between alien populations) are the consequence of genetic drift and random sampling from total genetic diversity of population - In other words alien population was founded by small number of individuals that carried a small (unique) part of original population’s alleles - Some of the original alleles were lost through drift and the final result was existence of populations that share small number of common alleles

- This phenomenon is relatively frequent in cases when a species is successfully transported (from original locality) into many different localities; new populations could be sources for further spreading (and they are more and more different from the original population, as well as they are from each others)

22334sf

Baker & Moeed (1987)

Conclusion: general rule about relationship between genetic diversity and situation in the introduced population (i) Genetic diversity of introduced population will be lower if transport vector brought a

small number of propagules from the original „source” (Nei et al. (1975) – smaller number of founders – smaller population growth (in the new habitat) – more genetic diversity lost

(ii) Genetic diversity of introduced population will be higher if a larger number of propagules is introduced (the larger it will be if larger area of source populations is „sampled”) + numerous repetitive introductions (eg. Biocontrol organisms, esthetical…) (iii) if circumstances in the new habitat cause that introduced population doesn’t grow (after initial introduction) and stay small for a long time, genetic variability will be lost, (even is number of initial propagules was high)

Low genetic diversity – small propagule source

Genetic diversity of alien populations will be reduced if transport vector „works”

sporadically (temporary and spatially)

Genetic erosion will take a place in the case of drastic bottleneck (less than 10

propagules) and when there are no repetitive introductions of propagules

Increased diversity as a consequence of mixing two (or more) genetically divergent populations

Higher genetic variability is expected in areas where alien species was introduced if: 1. “source” population is genetically structured (geographical pattern) 2. Transport vector covered well the whole area of source population (possibly during a few independent occasions) Basically, human mediated introductions enable distinct populations (of the same species) to get in contact in the new habitat. These kind of populations are called admixture populations

22334sf

Conditions after introduction and genetic diversity Influence of conditions in the new habitat onto introduced species is two-folded: 1. Even if a large number of propagules is introduced, genetic diversity loss is possible because it is possible that just a part of introduced individuals will reproduce (and transfer just a part of genetic info onto the next generation)

- Effective population – part of population that is mating randomly and, in that way, keep the gene flow on the source population level - Hence, we could expect variation in the level of genetic erosion in the alien population, depending on the species life cycle

2. The loss of genetic diversity could happen if introduced species grow slowly during a long period of time (K species) or many introduced individuals are lost after introduction

Genetic background and success after introduction into new habitat

As previously seen genetic diversity in the newly established population doesn’t have to

be lower (it can be even higher) than genetic diversity in the source population

How does the level of genetic diversity influence onto establishment success of the

introduced population?

Influence of genetic diversity loss onto the invasive success

- There are plenty of arguments in favour of postulate that the loss of genetic diversity influence negatively onto establishment success

- bottleneck and genetic drift could result in fixation of harmful alleles and lower the population adaptation capacity

- fixation of harmful alleles can cause increased mortality or reduced fecundity, and as a consequence population size decreases

Hybridization and invasive success

Quite a few studies on invasive success of hybrids between native and alien species - Already mentioned that hybridisation has a negative impact on the native species (lower fitness or introgression)

- Mating between two previously separated populations of the same species (admixture) or different (close) species could give alien population evolutionary „ momentum” to become invasive. Evolutionary momentum represented by the novel recombination of genetic elements, or an increase in overall genetic or phenotypic variability.

22334sf

Why do hybrids become invasive? Ellstrand & Schierenbeck (2000) – suggest hypothesis how hybridisation could increase invasibility: (i) Emergence of new genotypes, (ii) High genetic variability that ensure survival in all kind of conditions (iii) Hybrid vigour (strength) that emerge through heterozygosity or through disappearance of „harmful” genes or suppression of their expression

inbreeding Outbreeding

The most accepted hypothesis is: Emergence of new genotypes which leads to higher fitness and adaptation capability

Local adaptation and life history evolution

- Alien population members are limited in growth, reproduction and survival with a new set of factors (in the new habitat) that is probably different from factors in their original

- If any of environmental factors constantly influence the alien population, some of phenotypes will be selected and we can expect that population will evolve in the direction of the most adapted phenotypes (and they will continue spreading and influence onto a new area)

Conclusion: - Relocations cause genetic restructuration – it can lead to higher rates of spreading (to new areas) and ecological influence onto new habitats and native species. - Alien populations, once established, could be morphologically (or in their life cycle) different from other populations, sometimes those changes could help them to become invasive in the new habitat (fare away from their origin)

- claws are larger compared to signal crayfish from the native range, what is one of the features that gives them competitive advantage over other species, and could explain their invasive success

Kolbe et al. (2004) showed that substantial increases in genetic diversity of invasive populations can occur and can be explained by multiple introductions, especially when source populations are genetically divergent. Both interspecific hybridization and intraspecific admixture seem to be possible stimuli of invasion success in those cases.