Population Ecology By Dr Zaryab Khalid Class BS

Population Ecology By Dr. Zaryab Khalid Class: BS Botany Semester: 7 th Subject: Community Ecology

Why is it important? • assessing health of population • determining endangered or threatened status • predicting population dynamics

Population size … is the number of individuals present at a given time. The passenger pigeon was once North America’s most numerous bird, but it is now extinct.

Population density … is the number of individuals per unit area. In the 19 th century, the flocks of passenger pigeons showed high population density.

Population distribution …is the spatial arrangement of individuals. a) Random b) Uniform c) Clumped

Population growth Populations grow, shrink, or remain stable, depending on rates of birth, death, immigration, and emigration. (crude birth rate + immigration rate) – (crude death rate + emigration rate) = growth rate

Two Modes of Population Growth Exponential growth 2. Logistic growth 1. � Represent two different growth patterns or S trategies of populations

Exponential Growth �Also known as a J-curve �Growth is a fixed percentage of the whole (e. g. , 10% per day or year) �Population is growing at its full biotic potential

Exponential growth in a growth curve Population growth curves show change in population size over time. Scots pine shows exponential growth

Biotic Potential �Maximum possible growth rate of a population. �Absence of limitations to growth �Example: � 2 cats plus all their kittens make how many cats in 10 years? � 2 litters/year � 2. 8 surviving kittens per litter � B reeds for 10 years (“ breeding life” ) � 80, 399, 780 cats!!!

Can Populations Grow Forever? Population Biotic Potential Carrying Capacity: J curve MAXIMUM number of individuals that can be supported • in a given AREA. • FOREVER. Time Copyright © The Mc. Graw-Hill Companies, Inc. Permission required for reproduction or display.

Oscillations: • Populations overshoot the carrying capacity and experience a dieback • Can be regular or irregular • Overshoot When a population surpasses the carrying capacity of its environment or population explosion • Dieback Population crash

Population growth: Oscillations S ome populations fluctuate continually above and below carrying capacity, as with this mite.

Population growth: Dampening oscillations In some populations, oscillations dampen, as population size settles toward carrying capacity, as with this beetle.

r-Selected Species �r = Growth rate �Reproduce young �High reproductive rates �Many small offspring �S hort-lived �Found in unstable or unpredictable environments

Examples of r-Selected Species �Weeds, bacteria, insects, algae, small mammals

Logistic Growth �Also known as S - curve �Growth slows as the population approaches Carrying Capacity �Populations stabilize at carrying capacity

K-Selected Species �K = Carrying Capacity �Reproduce later in life �Low reproductive rates �Fewer large offspring �Long-lived �S table or predictable environments

Examples of K-Selected Species �Elephants, great apes, hippopotamus, whales, humans (? )

What Determines Population Size or Carrying Capacity? Environmental Resistance All the limiting factors that tend to reduce population growth rates Balance between biotic potential & environmental resistance determines growth rate

LE 4 -1 Environmental resistance Stabilized population size Ex po ne nt ia lg ro wt h Carrying capacity Limiting factors: Water Space Food Predators Disease