Anne Bjorkman - Coexistence theory and invasive species Flashcards
Niche theory
Species coexist because they occupy different niches. Two species with identical niches cannot coexist forever. Leads to competitive exclusion principle.
Niche
The environmental requirements of a species (when, where and how a species makes it living).
Fundamental niche
The environmental factors permitting a species to survive and reproduce.
Realized niche
Where the species actually occurs, limited by interactions with other species. “Part” of the fundamental niche.
The most important factor according to niche theory
Biological interactions. Competition leads to niche differentiation.
Criticism of niche theory
Seems unlikely that there are as many niches as species in the world.
Disturbance theory
When one species becomes to dominant, something happens that knocks it back. Parasites often makes it less fit. Could also be frequent disturbances or predation. This allows coexistance.
Neutral theory
Species are very similar in their competitive abilities. Competitive exclusion is too slow. Species distribution is largely due to chance. All species have an equal chance to “win the lottery”, also called lottery theory.
Niche vs neutral theory
Neutral often accurately describes real patterns of diversity in very diverse communities, like rain forests. This doesn’t mean that it is correct, though.
Communities are shaped by both niche and neutral processes.
Invasive species
A plant, animal or other organism that is not native to a specific location (alien species), and has a tendency to spread and causes harm and damage to the environment, economy and/or human health. There are many alien species, but not that many invasive species.
Reasons for introduction of new species
Inentional:
Wanting to feel at home.
Horticulture and pet trade.
Food/forage organisms: fish, pasture grasses etc.
Biocontrol agents.
Unintentional:
Ship ballast water.
Grain shipments.
“Stowaways”.
Invasion process
Uptake from native range, transfer via vector, release in new region, establishment, population increase and range expansion.
The tens rule
1/10 of the species that arrive will survive.
1/10 of the species that survive will establish.
1/10 of the species that establish will become invasive.
About 1/1000 of the species introduced to a new continent will become invasive.
Ecological impact of invasion
“Dilution” of native biodiversity.
Direct impact on native species populations via competition, predation, disease.
Ecosystem level change.
Dilution and competition invasive species
Effects abundance and local diversity, even though they often don’t cause extinction.
Populations decline/extinction invasive species
Introduced predators can cause great damage, particularly on islands with “naive” prey.
Altering the ecosystem invasive species
Most common in plants. Alter the ecosystem processes.
Economic impacts of invasive species
Reduced agricultural productivity
Forest damage
Clog water intakes
Choke waterways
Health costs
Costs a shit load of money
What makes a species invasive?
The most important factor is how many individuals of the species that are introduced, and how often: propagule pressure.
Invasive species tend to be larger, grow faster and have a “live fast, die young” life strategy.
Enemy-release hypothesis
An alien species is more successful in its new range because it lacks co-evolved pathogens/predators.
Novel weapons hypothesis
The new species has a trait that the new habitat is not used to, and have no defense for. Could be toxins in plants.
Do invasive species perform better in their new ranges?
Yes.
Factors that make a habitat more invasable
Empty niches
Lack of enemies of invader
Disturbance - human related
Anthropogenic habitats - human related
Naive prey
How to limit species invasion
Prevention, eradication and control of exotic species.
Prevention of introduction, e.g. exchange ballast water mid-ocean.
Possible to eradicate invasive animals on islands, but very difficut for plants and on the mainland.
Biological control: introduce natural enemies to control invasive species. Can go very wrong, but also be very effective.
