BIOL 4120: Principles of Ecology Lecture 9: Properties of Population Dafeng Hui Room: Harned Hall 320 Phone:

Population Ecology What is a Population? What is a Population? What constitutes an individual? 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 Unitary or modular Aspen seagrass

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

Distribution Distribution Spatial location, Area over which a species occupiesSpatial location, Area over which a species occupies Geographic range Geographic range Area that encompasses the entire population of a speciesArea that encompasses the entire population of a species Limited by climate Limited by climate Direct: temperature, precipitation …Direct: temperature, precipitation … Indirect:Indirect: Food production Food production Water supply Water supply Habitat Habitat Incidence of parasites, pathogens and competitors Incidence of parasites, pathogens and competitors Geographic barriers Geographic barriers 9.1 Distribution of a population

Influenced by available habitat Influenced by available habitat TemperatureTemperature Red Maple Red Maple -40 o C-40 o C Carolina wren Carolina wren Northwards - 7 o CNorthwards - 7 o C Westward>52 mmWestward>52 mm When all environmental factors within its range of tolerance, the organism can live in its habitatWhen all environmental factors within its range of tolerance, the organism can live in its habitat Horned lark Horned lark Avoids forestsAvoids forests Available territoryAvailable 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 (pH is acidic) Local subpopulations Distribution of moss Tetraphis

Abundance (number of individuals in a population) Abundance (number of individuals in a population) =distribution area * population Density =distribution area * population Density Density can be a key factor Density can be a key factor Number of individuals per unit spaceNumber of individuals per unit space Distribution patterns Distribution patterns 1. Random: Equal chance of being anywhere. 2. Uniform distribution of resources. Regular: Uniformly spaced. Regular: Uniformly spaced. Exclusive use of areas.Exclusive use of areas. Individuals avoid one another.Individuals avoid one another. 3. Clumped: Unequal chance of being anywhere. Mutual attraction between individuals.Mutual attraction between individuals. Patchy resource distribution.Patchy resource distribution. 9.3 Abundance reflects both population distribution and density

Distribution of Individuals on Small Scales

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

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

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

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

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 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 In theory, populations of sexually reproducing organisms tend toward a 1:1 sex ratio (males to females) In theory, populations of sexually reproducing organisms tend toward a 1:1 sex ratio (males to females) In mammalian pop., In mammalian pop., at birth1.05 < > > CIA 2006 data. (See slide showed before)

Sex ratio changes with age groups: age pyramid

Sex ratios in populations shifts with age Sex ratios in populations shifts with age HumansHumans More males at birth More males at birth Males have shorter life span Males have shorter life span WarWar High risk activitiesHigh risk activities Females need to survive giving birth to children Females need to survive giving birth to children

9.7 Individuals move within and among populations Movement of individual will influence the sub-population density Movement of individual will influence the sub-population density DispersalDispersal EmigrationEmigration ImmigrationImmigration

Dispersal: movement of individuals in space. Dispersal: movement of individuals in space. Method of dispersal 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, Emigration: an individual moves out of a subpopulation Emigration: an individual moves out of a subpopulation Immigration: an individual moves from another location into a subpopulation Immigration: an individual moves from another location into a subpopulation

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. Migration: a round trip

9.8 Distribution and density change in both space and time Distribution and density of population change with space and time 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. 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. Many causes such as: dispersal, immigration, emigration, and temporal changes in environmental conditions.

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

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

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