BIOL 4120 Principles of Ecology Lecture 9 Properties

BIOL 4120: Principles of Ecology Lecture 9: Properties of Population Dafeng Hui Room: Harned Hall 320 Phone: 963 -5777 Email: dhui@tnstate. edu

Population Ecology n n n What is a Population? What constitutes an individual? • Easy for most large sexually reproducing animals (humans, dogs, cats etc) • Not so easy for colonies of animals and many plants • Trees (Ramets) • Coral Unitary or modular Aspen seagrass

n n n Properties of Population Most important property is abundance of population which is determined by its distribution and density. Populations have • Distribution • Density n How to determine population density? • Age structures • Different sex ratios along time • Changes in distribution and density due to dispersal, emigration, immigration and migration. • Distribution and density change in both space and time

9. 1 Distribution of a population n Distribution • Spatial location, Area over which a species occupies n Geographic range • Area that encompasses the entire population of a species n Limited by climate • Direct: temperature, precipitation… • Indirect: n n n Food production Water supply Habitat Incidence of parasites, pathogens and competitors Geographic barriers

n Influenced by available habitat • Temperature n Red Maple • -40 o. C n Carolina wren • Northwards 7 o C • Westward>52 mm • When all environmental factors within its range of tolerance, the organism can live in its habitat n Horned lark • Avoids forests • Available territory

Tiger Beetle of Cold Climates

9. 2 Distribution of a species varies at different spatial scales Continental scale: climate suitability Particular area: microclimate and stream banks (coniferous trees and abundance) Within a particular locality: occupy stumps of conifer trees (p. H is acidic) Local subpopulations Distribution of moss Tetraphis

9. 3 Abundance reflects both population distribution and density n n n Abundance (number of individuals in a population) =distribution area * population Density can be a key factor • Number of individuals per unit space Distribution patterns 1. Random: Equal chance of being anywhere. 2. Uniform distribution of resources. Regular: Uniformly spaced. • Exclusive use of areas. • Individuals avoid one another. 3. Clumped: Unequal chance of being anywhere. • Mutual attraction between individuals. • Patchy resource distribution.

Distribution of Individuals on Small Scales

9. 4 How to measure density? n Direct Counts • Time consuming • Needs to be sure you can see all individuals in the area n 1. Quadrates • Organisms must be static • Needs laying of quadrates to be random • Statistical analysis essential n Sampling 2. Mark and recapture • Estimate n n n n Assumes equal chance of capture for all No deaths or births Marked animals random among unmarked No loss of marks No emigration or immigration Other factors include time of capture, stress of capture, sex, age, etc. Additional sampling methods • The presence of an individual can be determined by tracks, bird song, etc • Get a relative measure

Capture-recapture or markrecapture methods n n n n Lab Suppose there is a population with size (N), trap, mark and release a known number of marked animals (M) After a period of time (well mixed with other animals) A sample of population with sample size (n) is recaptured. Among these, (R) animals are marked. Assumption: M/N=R/n N=n. M/R Example: M=39 rabbits, n=15+19=34, R=15 N=34*39/15=88

9. 5 Populations have age structures Age structure: the number or proportion of individuals in different age groups Age pyramids for three human populations in 1989.

n Techniques used for aging animal populations • Mark young individuals and follow their survival • Study a representative sample • Tooth wear • Plumage changes • Growth rings in teeth, horns, ear bones, and so forth

Some plant ages can be determined too Mark, DBH, ring Tree rings show annual growth (American beech, Fagus grandifolia)

n In plant populations, the distribution of age classes is often skewed because dominant overstory trees may inhibit the establishment of seedlings or the growth and survival of juvenile trees

An oak forest in England

9. 6 Sex ratios in populations shift with age n n In theory, populations of sexually reproducing organisms tend toward a 1: 1 sex ratio (males to females) In mammalian pop. , at birth 1. 05 <15 1. 04 15 -65 1. 02 >65 0. 81 CIA 2006 data. (See slide showed before)

Sex ratio changes with age groups: age pyramid

n Sex ratios in populations shifts with age • Humans n n More males at birth Males have shorter life span • War • High risk activities n Females need to survive giving birth to children

9. 7 Individuals move within and among populations n Movement of individual will influence the sub-population density • Dispersal • Emigration • Immigration

n Dispersal: movement of individuals in space. Method of dispersal Passive dispersal (gravity, wind, water, animal) seeds of plants, small animals, fish, shrimp. fruits and seeds ate and carried by animals (long distances) Active dispersal: animal movement, n Emigration: n Immigration: subpopulation an individual moves out of a an individual moves from another location into a subpopulation

Migration: a round trip Migration – A round trip, perhaps involving mating Red-necked ducks: Breeding in the north east Winter in South Carolina and Florida Gray whale: Winter in California, Summer in Arctic Migratory pathways of Ring-necked ducks and gray whale.

9. 8 Distribution and density change in both space and time n n n Distribution and density of population change with space and time Primary factors driving the dynamics of population abundance are the demographic processes of birth and death. Many causes such as: dispersal, immigration, emigration, and temporal changes in environmental conditions.

Invasive species Gypsy moth caterpillars $764 M loss in 1981 Defoliated oak forest

Invasive species Kudzu, an invasive species Native to Asia, introduced to US as an ornamental vine in 1876 Used to control soil erosion in 1930 s and 1940 s 1950 s, recognized as pest Cover southeastern US, 2 million to 7 million acres

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