Lecture 11a: invasive ecology 1 Flashcards
(21 cards)
Lecture outline
*What is a biological invasion, and why do they occur
*Classic invasion case studies
* Major patterns in invasions
* impacts of invasives
Biogeographic barriers and evolution:
The break up of Pangaea
-Long periods of continental isolation
-Evolution has resulted in differentiated biotas on continents
*Very diverse species on different continents
*Divergent evolution of species and traits
Continental drift summary from Pangaea 225mya to today
225 mya Permian era: all of the worlds land masses were connected forming one super continent Pangaea
200 mya Triassic era: two continents Gondwanaland to the south and Laurasia to the north
135 mya Jurassic era: the land mass that would become Oceania and Antarctica became detached from Gondwanaland
65 mya Cretaceous South America detached from Gondwanaland but temp. Connected to antarctica
Since then as sea levels have changed additional islands have emerged and antarctica partially submerged
Reference: A. R. Wallace’s Biogeographic Realms (“The Geographic Distributions of Animals”; 1876)
http://www.geo.biz/pangea.htm
Globalisation: Colonialism
*We’ve been at this for sometime; first wave under European colonialism
*Christopher Columbus in the Americas, on to British Empire, and other various empires that have gone before, during and after
*As an example, British Empire c.1911, pink are British
*Lines are shipping routes
Biogeographic barriers generally prevented the interaction of species from isolated continents until
Globalisation through the first wave of European colonialism : see map in notes
^ This image shows the extent of the british empire in 1911 with lines depiciting established shipping routes at the time.
In more recent years modern technology trade and transport has increased global connectivity:
Trade and transit increase
Airport links with thousands of flights occurring every day
Many accidental and intentional introductions as a result
Charles Elton is thought of as the founder of invasion ecology
He was the first scientist to catologue invasions uniting three main components:
-Over millions of years, continents have become distinct
-Human trade and travel are reducing these distinctions
-This process has major implications for conservation of diversity
He also put forward mechanisms explaining invasions
Example 1: Malaria mosquito
Anopheles gambiae s.l. (A. arabiensis)
-Native to Tropical Africa and Madagascar
-Accidental introduction by ships
-Malaria cases: 100,000s
-Malaria deaths: 10,000s
-Brazilian Government/Rockefeller Foundation eradication programme (larvicide and adult insecticide): > US $ 3 billion
Paramakelis et al. (2008) Am J Trop Med Hyg. 78: 176-178.
Killeen et al. (2002) The Lancet Infectious Diseases 2: 618-627
Malaria mosquito notes:
*1930s NE Brazil
*Within a decade had spread inland up the river system causing epidemics of malaria with hundreds of thousands of cases and tens of thousands of deaths
*Still a present threat; 2016/17 problem with Zika virus with another non-native mosquito vector
*Mosquito introduced from standing water in used tyres
*Improvements in biosecurity needed to avoid such instances
Example 2: Chestnut blight
Cryphonectria (Endothia) parasitica
-Fungal pathogen from Eastern Asia/Japan
-Infected American Chestnut (Castanea dentata)- 1 in 4 trees in Eastern forests were this species. Important forestry tree
-Imported to N America on nursery plants early 20th C
-1911: had spread to > 10 US states, losses US $ 25,000,000
-1950: Most trees dead
-Efforts to breed resistant strains
Notes:
*Fungal pathogen example
*Arrived in N. America in early 1900s
*Probably heard of Dutch Elm disease in UK and Europe; this is a similar thing and cause similar problems
*Efforts to produce a resistant strain by breeding with chestnut which occurs in pathogen’s native range, with co-evolved resistance
Example 3: European Starling
Sturnus vulgaris
-From Eurasia
*Another example of colonialism being the cause if invasion
*American Acclimatization Society (Eugen Schieffelin) tried to establish the starling in Central Park three times. Their aim was to introduce all bird spp. from Shakespeare!
-3rd attempt to establish in NY Central Park successful (~80 birds)
-Introduced in 1896, and then progressed to other states along the north east coast of America
-Now ~150 million birds, from S Canada to Mexico
*Now 150m birds and widespread and beyond the Americas
Example 3: Japanese knotweed
*Fallopia japonica
-Collected from Japan, brought to Holland by Philipp Franz von Siebold
Considered such a hardy, vigorous growing plant it was awarded many prizes by horticultural societies -Awarded Gold medal by Society of Agriculture and Horticulture of Utrecht – making it desirable for gardeners to utilise
-1850: Specimen added at RBG Kew
-Widely sold and planted
-Vigorous vegetative growth: one female clone in Europe
*Added to Kew as a good replacement for bamboo
*Consequently, widely sold and planted since 1850
*Only introduced one phenotype
-Damage to infrastructure
*Very vigorous vegetative growth – damages buildings irreparably the building is demolished the foundation dug out and soil needs to be sterilised
*Under UK Wildlife and Countryside Act, illegal to transport it or move it into the wild, or allow it to
Example 5: Sea lamphrey
see: https://www.youtube.com/watch?v=9JQ6oHjpeqU
Petromyzon marinus
-N Atlantic species, spawns in streams
-Improvements to Welland Ship Canal in 1919
-Spread to Lake Huron (1937) and Michigan; Lake Superior (1946)
-Hunting predator and ectoparasite
-Decimated commercially important lake trout populations
-In 10 yrs, catch fell from 3900 Tonnes to <12 Tonnes
Additional lamphrey notes:
*Life cycle which involves them being adults in the sea: anadromous
*Migrate up streams, like salmon
*Occurs in N. Atlantic occurs in streams in E and N America but has moved into the Great Lakes system due to the Welland Ship Canal which connected Lake Ontaria and Lake Eerie
*Very quickly spread into the other lakes within the system
*Not just ecological impacts but economic too
Invasion as a process
*Invasions represent a process
*They don’t happen as soon as you introduce a species
*We have our introduced species, and that species needs to be able to reproduce
*It needs to be able to establish its own self-sustaining population, independent of human intervention
*At that point we can then say it has become established
*Sometimes you’ll see this termed naturalised, especially for plants
*Not all species that are introduced will get to this stage
*Maybe they aren’t able to reproduce, or can’t survive in the new climate, or some other limitation
*Some of those species which can establish, will also go on to establish new populations, disperse and increase their range size to the point where they may become dominant in various communities and habitats, at which point we can refer to them as invasive
Invasion process
^ Invasion Process as a graphical representation
Stage 1: Naturalisation
Self-sustaining population/s independent of human intervention
Stage 2: Lag Phase
Species persists, but does not spread or increase in frequency
Stage 3: Invasion
Near exponential increase in frequency and
distribution, new populations establish:
may have taken dispersers a little time to recognise as a suitable food source, if producing fruits
*After primary invasion, one of two possibilities
*We might get the species occurring in all the habitats where it can occur, and now occupies all of the climatic niche that it can occupy in the new range and can’t go any further – essentially reached some kind of carrying capacity and persist at that high level
*We might get a secondary invasion; some time passes, maybe the species is evolving over time, perhaps there are strong selection pressures acting on genotypes of this species which then result in it being able to establish in quite different habitats or climates from where it was first introduced, and at this point we may see a further increase in range size and frequency
*Alternatively, the species may decline – why?
*Natural enemies; adaptation of existing natural enemies already present or movement of prior enemies
*Beware the terminology of invasive species and the CBD definition here
CSR Strategy
Competitors (C): These plants thrive in stable, resource-rich environments and are highly competitive for resources.
Stress-tolerators (S): These plants are adapted to harsh, stressful environments where resources are scarce or conditions are extreme.
Ruderals (R): These plants are adapted to disturbed or transient environments and are quick to colonize and reproduce in such areas
^ see: Ricotta, C., Dalle Fratte, M., Pierce, S., Carboni, M., Cerabolini, B.E.L. and Pavoine, S. (2023) ‘Quantifying the extent of plant functional specialization using Grime’s CSR strategies’, Ecological Indicators, [online] 148, 110066. Available at: https://doi.org/10.1016/j.ecolind.2023.110066 [Accessed 28 Mar. 2025].
Major patterns in invasive species
Intercontinental variation and flows:
-Where are invasion hotspots globally?
-Which regions are major donors and recipients of invasive species?
Invasions of islands
-Why are there so many naturalised and invasive species on islands?
Where have they been in the past and where might they be in the future?
Latitudinal patterns
-Are there more naturalised and invasive species in temperate than tropical regions, and if so why?
We’ll look at the flow of invasive species; where do they come from, where are the donors?
Why are certain ecosystems more prone to invasion?
The Global Naturalized Alien Flora (GloNAF)
See map figure in notes
van Kleunen, Dawson, Essl, Pergl, Winter et al. (2015) Nature 525: 100-103
Very few naturalised invasives in some countries and also some major hot spots usually small islands but also coastal USA has high levels of issues often distribution relates to port areas
*We’ll be focusing on plants, and this was done for this work on Glonaf
*An inventory of naturalised species in a given country
*This is a nice summary of the work allowing us to see the hotspots on a global scale
*More than 13k plant species which have naturalised, globally
*To put into perspective, 400k known plant species so ~ 4%
> 13,000 introduced plant species are naturalized somewhere (~4% of world flora)
See GLONAF figure - these are the hotspots (including Hawaii) Van Kleunen et al.
Global flows of naturalized plants: which continents are the biggest exporters and importers?
Estimates of species richness per continent based on the Kew’s World Checklist of Plant Families (http://apps.kew.org/wcsp)
*The point of this work was to look at both where species end up but also where they came from
*Which are the biggest exporter and which are the largest importers
*Essentially, we would expect continents with the largest number of species to be the largest exporters, if just due to chance
*Species richness based on Kew’s World Checklist
*As you might expect, countries with large tropical regions have the greatest diversity and the northern temperate regions less so
(see Van Kleunen et al 2015)
Based on species richness estimates, we would expect S America to be the biggest exporter….
But actually, Temperate Asia and Europe have exported the most – why?
Based on chance alone, we might expect a pattern something like this on the left; e.g. exporting species from S. America since it has the highest diversity
*Wedge size is proportional to diversity
*Compare that to what it actually seen
*Temperate Asia is actually the biggest contributor, followed by Europe; difference is quite notable
Due to:
*Globalisation
*Colonialism
*Connection to other continents
*Large land masses of continental Asia
Invasion of islands
Dawson et al 2017 Nature Ecology and Evolution
*We can also look at different taxonomic groups, including plants, but also insects, reptiles, etc.
*Across 8 different taxonomic groups, which parts of the world harboured the most naturalised species
*Red we can see the hotspots
*Once accounted for sampling effort and area, most of the top invaded regions were islands
*Hawaii, Singapore, New Zealand
*But why?
Latitudinal patterns
Lower numbers of naturalised species at lower latitudes (the Tropics) :
-Relative to area
-Relative to native species
Why are there fewer invaders in the tropics?
See:Guo et al. (2021) Journal of Biogeography 48:253–262
Additional notes on latitudinal patterns:
*From the GLONAF database, interested in differences between continents, climate and latitude in terms of the number of naturalising species that occur
*As you might expect, peak in native species per unit area in tropical regions
*And when we look at the naturalising introduced species we can see we’ve got the inverse; this dip around the equator; not as many in the tropics
*If we standardise that according to the number of native species, you can see we have this peak at around 40-50 degrees north, and the same to the south
*Lower numbers of naturalising species relative to natives and area
*But why?
*Biotic resistance; such high species richness, saturation of niche space
Summary
*Invasions result from introductions of species over long-held biogeographic barriers by humans
Invasions are a process:
-Introduction → survival → establishment → spread → ecological impacts
*Species can be introduced intentionally or unintentionally, by multiple pathways
*Islands are heavily invaded
*There are more introduced species at mid-latitudes
