BIOL-2140: Chapter 12

Population Dynamics over Time and Space

Population dynamics

variation in population over space or time

Red deer example

population fluctuations

Over 30 years, population of red deer on Isle of Rum in Scotland as remained relatively stable

Lake Erie example

population fluctuations

over a single year, algae population in Lake Erir exhibits wide fluctuations from 0-7,000 cells per m³

Small organisms tend to:

reproduce faster than larger organisms

respond faster to favorable/unfavorable conditions

Larger organisms have:

lower SA:V ratio

allows them to maintian homeostasis in the face of environmental changes

Age structure fluctuations

when age group contains high/low number of individuals, population likely experienced high birth/death rates in the past

White fish example

age structure fluctuations

Researchers determined age of white fish by examining their scales; in 1947, large number of 3 year old fish; this cohort continued to dominate in subsequent years

Age determination for forests example

age structure fluctations

removed sample of wood from trunks to count growth rings; 1500s, largely composed of oak trees; fire and drought increased white pine trees; allowed beech and hemlock to grow

Overshoot

when population grows beyond its carryin capacity

Die-off

substantial decline in density that typically goes well below carrying capacity

Population cycles

regular oscillations of population over a longer period of time

Gyrfalcon example

cyclic population fluctuations

18th century, gyrfalcons captured and exported from Iceland for EU nobility; unti 1770, gyrflacons intensely sought and records indicate 10 year cycle in falcon abundance

Delayed density dependence

when density dependence occurs based on population density at some time in the past

Moose breeding example

Delayed density dependence

Moose breed in fall; if K is high, many parents will breed; reduced resources in spring may not support all offspring

Damped oscillations

0.37 < rt < 1.57

stable limit cycle

rt > 1.57

Habitat fragmentation

process of breaking up large habitats into number of smaller habitats

Owl fragments example

Black regions: small fragments of forested habitat where owl lives

Lines: potential dispersal paths of owls between patches of forest

Numbers: estimates of how many owls could live in each of the patches

Rescue effect

dispersers supplementing a declining subpopulation that is headed toward extinction

Black-footed ferrets example

rescue effect

ferrets had substantial habitat loss; initital captive breeding failed; small population discovered and captive breeding successful; created metapopulation resistant to complete extinction