Lecture 4 - Population Ecology III
In real life, it’s not usually tidy (Logistic and Exponential):
Time lags in population response to increased density
Carrying capacity is an example of population regulation (a way which allows species to
Many factors regulate populations: change the size and growth rate of populations.
Some factors are density dependent factors: the importance of the factor in changing the
population depends on the size (density) of the population. Usually: ↑ density = ↑ overall impact
• Resource consumption (provided w/ x amount of resources)
• Health: Starvation, Disease Spread, Parasites!
• Territoriality / Mating
• Waste accumulation
• Intrinsic (behavioural) factors (ie killing each other
off for space)
Some factors in the environment are (extrinsic) density-
independent: they are external to the population and the
impact does not depend on the size of the population
(these are abiotic processes)
• Availability of many resources
• Climate variation Lecture 4 - Population Ecology III
• Natural disaster
Population Regulation in Daphnia spp: -->
Density-dependent regulation of
Escaping regulation – how some
species boom (suspectible to
decline in resources leading to a
• Invasive species are organisms
that are able to spread uncontrollably. In other words, they do not experience adequate
• Invasive species are usually introduced from their native range to a new area (on
purpose, have large impacts). In its new habitat, we call the species non-native,
exotic, or alien. BUT non-native species are not always invasive.
• When they are introduced, non-native species sometimes escape their predators,
pathogens, and parasites. These forms of regulation are not transferred or
cannot survive in the new habitat.
• Non-native species may also adapt to acquire more resources or utilize new
Invasive species often share some common traits (outcompete native species)
• Few predators (or herbivores, for plants). These may be ‘left behind’ in the native range.
• Adaptable. Population bottlenecks and strong selection pressures in the new range
select robust, adaptable phenotypes.
• Reproduce quickly. A key trait of invasive species: they have higher fecundity than their
• Thrive in disturbed ecosystems. Invasive species are often human adapted, meaning
they thrive under conditions of human disturbance. They also tend to acquire resources Lecture 4 - Population Ecology III
quickly and use them quickly, which takes advantage of the resources released by
• Out-compete native species for resources. All the above traits combine to make
highly competitive species who suffer fewer population regulations and acquire a larger
share of resources than their neighbours.
Population Regulation can have Large-Scale Consequences!
• The Mountain Pine Beetle (Dendroctonus ponderosae) is a bark beetle native
• The MPB normally helps