Life Table Problem• In a population of field mice, 50% of an original cohort of females

survive long enough to breed as one year olds. At that time they give birth to three female offspring. 50% of the survivors will live long enough to breed as two year olds. Again they will give birth to three female offspring. Once again 50% of the survivors will live long enough to breed as three year olds. They will again give birth to 3 females. All of the survivors will die once they reach 4 years old due to old age. They will not reproduce as four year olds. What is the net reproductive rate (Ro) for this cohort of field mice? (Hint: you only need to calculate lx and mx to be able to solve for Ro – (Ro = lxmx).)

• lx is proportion surviving to age x

• mx is number of offspring per survivor at age x

Competition

Competition

Competition is an interaction between individuals, brought about by a shared requirement for a resource in a limited supply, leading to a reduction in the survivorship, growth, and/or reproduction of the competing individuals

Competition

Competition

Competition

Two key points:

1.Resource being competed for must be limited in supply

2. Interaction is always negative

Competition

Intraspecific competition - competition between members of the same species - thought to be especially strong because members of the same species have the same resource requirements – regulates population size

Interspecific competition - competition between members of different species - can be very strong as well – also regulates population size, structures communities, influences natural selection

Mechanisms of Competition

1) exploitation competition (aka resource or scramble) - individuals exert negative influence on each other by using up resources that each need - competition is mediated indirectly through resource depletion - individuals don't need to come into contact to compete

2) interference competition (aka contest competition) - competitors directly interact with each other in the course of seeking a common resource

Coral reef community – Great Barrier Reef

Competitive Asymmetries

• Although competition has negative effects on the population as a whole, some individuals are more negatively effected than others

Flax

Orchard Grass

Territoriality

• Territoriality occurs when there is an active interference such that a more or less exclusive area, the territory, is defended against intruders by a recognizable pattern of behavior - individuals or groups are spaced out more than would be expected from a random occupation of suitable habitats

Golden-winged sunbird

Limpet – Patella cochlear

Patella grazing on crustose algae (A)

Patella Limpet grazing exclusion

Corn

Law of Constant Final Yield