Lecture 5
Major Vectors Continued
Legal and Illegal Pet trade
• The legal pet trade imports tens of millions of vertebrates and
invertebrates annually. Careless handling, misidentified species,
inadequate quarantine, owner releases all contribute to invasions
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The illegal pet trade is problematic for all of the same reasons
above but also because the health of the organisms is not evaluated,
thus they can be sources of exotic disease propagules.
Establishment
Rule-of-Tens
One in ten imported organisms appear in the wild. Of these, one in ten become
established, and of these, one in ten become invasive.
Therefore ~0.1% of original pool are invasive
Broadly applied but not all organisms fit the pattern
The central idea is useful, that a large proportion of species surviving each step
in the invasion process is eliminated in the next step so that very few actually
become important invasives (= the process of a diminishing cascade or
funneling).
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Propagule Pressure
Propagule = individual(s) released into a non-native environment
Probability of successful establishment depends on
(1) the number of propagules introduced
(2) the number of introduction events
(3) an interaction between 1 and 2
Why is propagule pressure important?
The larger a population is and/or, the larger the area it occupies, the less
likely it is to go extinct
• Both components of propagule pressure, number of individuals introduced,
and the number of independent introductions may influence different
population characteristics
• Number of individuals introduced can overcome demographic
stochasticity and density-dependent forces such as Allee effects.
• Number of independent introductions can reduce the influence of
negative spatially patterned forces (e.g. environmentally stochastic
forces such as climate or biotic interactions).
• Both processes can influence genetic variation
Disturbance
• Any discrete event that disrupts ecosystem, community, or population
structure and changes resource availability or physical environment. Can
look at the effects of disturbance on ecosystems at many different levels.
• Natural vs Anthropogenic
• Biotic versus Abiotic
Scale, intensity, frequency, duration, predictability
• Endogenous vs. exogenous (part of system or imposed by outside
forces)
A basic tenet of community ecology
• Disturbance creates vacant space, releases resources, alters species
interactions
Long held that disturbance necessary for invasive plants to establish
(Disturbance facilitates invasion)
Gross oversimplification!
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