Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 9 Population Distribution and Abundance

Terminology Population (def.): A collection of all organisms of a single species living in a specific geographic area

Niches Niche: Summarizes environmental factors that influence growth, survival, and reproduction of a species. Niche: Summarizes environmental factors that influence growth, survival, and reproduction of a species. –Grinnell’s definition focused on the effects of the physical environment –Elton’s definition included biotic and abiotic factors

Niches Hutchinson defined niche as: Hutchinson defined niche as: –n-dimensional hyper-volume n equates the number of environmental factors important to survival and reproduction of a species. n equates the number of environmental factors important to survival and reproduction of a species. –Fundamental niche - hypervolume –Realized niche includes interactions such as competition that may restrict environments where a species may live.

Population Ecology PopulationCharacteristicsDispersionDensity Sex Ratio Age Distribution Growth Rate (#organisms / time) Birth Rate Immigration Death Rate Emigration

“Large-scale” patterns of distribution: “Large-scale” patterns of distribution: Refer to variation in species abundance w/in range Refer to variation in species abundance w/in range –due to variation in habitat quality

Describing Where a Species Lives Range Range –Geographic description – Where on a map ? –“Large-scale” distribution

Kangaroo Distributions and Climate Caughley - relationship between climate + distribution of three largest kangaroos in Australia Caughley - relationship between climate + distribution of three largest kangaroos in Australia

Macropus giganteus – eastern grey Eastern 1/3 of continent temperate forest, tropical forest

Macropus fuliginosus – western grey southern and western regions temperate woodlands and shrubs

Macropus rufus – red arid / semiarid interior

Distributions largely based on climate

Kangaroo Distributions and Climate Limited distributions may not be directly determined by climate. Limited distributions may not be directly determined by climate. –Climate often influences species distributions via: food production food production water supply water supply habitat habitat incidence of parasites, pathogens and competitors incidence of parasites, pathogens and competitors

Describing Where a Species Lives Habitat Habitat –Ecological description –What environmental conditions ? –Determined by: Terrestrial Environments: Climate / Elevation / Soil conditions / Topography Terrestrial Environments: Climate / Elevation / Soil conditions / Topography Aquatic Environments: Water depth / Temperature / Nutrient concentration Aquatic Environments: Water depth / Temperature / Nutrient concentration

Fatal Sub-Optimal Optimal Sub-Optimal Fatal Environmental Gradient Population Size No Stress Good Habitat Poor Habitat Poor Habitat Environmental Conditions and Habitat Stress

Habitat Quality Resource Utilization = Habitat Space Area Volume x Resource Concentration Resources Energy per unit space x Time to Acquire Resources Hours / day Days / year What Defines Habitat Quality ? Capacity of the environment to support a population

Habitat Quality Resource Utilization = Habitat Space Area Volume x Resource Concentration Resources Energy per unit space x Time to Acquire Resources Hours / day Days / year What Defines Habitat Quality ? Limited by: Physical barriers Environmental requirements

Habitat Quality Resource Utilization = Habitat Space Area Volume x Resource Concentration Resources Energy per unit space x Time to Acquire Resources Hours / day Days / year What Defines Habitat Quality ? Controlled by: Light availability, Precipitation, Soil characteristics, Water depth, Prey abundance Prey abundance

Habitat Quality Resource Utilization = Habitat Space Area Volume x Resource Concentration Resources Energy per unit space x Time to Acquire Resources Hours / day Days / year What Defines Habitat Quality ? Controlled by: Daily / Seasonal variation in temperature, precipitation, and nutrient availability

Figure 9.3 Habitat Generalist Habitat Specialist

Figure 9.4 This temperature occurs everywhere This temperature occurs only in some high elevation habitats

Distributions of Barnacles - Intertidal Gradient Organisms in intertidal zone have evolved different degrees of resistance to drying Organisms in intertidal zone have evolved different degrees of resistance to drying –Barnacles - distinctive patterns of zonation within intertidal zone

Connell found pattern in barnacles: Chthamalus stellatus restricted to upper levels; Balanus balanoides limited to middle and lower levels Chthamalus stellatus restricted to upper levels; Balanus balanoides limited to middle and lower levels

Distributions of Barnacles Along an Intertidal Gradient Balanus - more vulnerable to desiccation, excluded from upper intertidal zone Balanus - more vulnerable to desiccation, excluded from upper intertidal zone –Chthamalus adults excluded from lower areas by competition with Balanus

Competition? How do we know that Balanus outcompetes Chthamalus?

Distribution of Individuals on Small Scales

All Species Have Clumped Dispersion At Large Spatial Scales A species occurs only in locations where environmental conditions are suitable for metabolic activity, resource acquisition, and reproduction

Geographic Scale: Latitudinal / Longitudinal gradients of climate. Barriers to migration (Oceans, Mountain ranges) All Species Have Clumped Dispersion At Large Spatial Scales

Topographic Scale: Variation in temperature, precipitation, soil conditions at different elevations and slope positions (e.g., upper, lower, N-facing, S-facing) All Species Have Clumped Dispersion At Large Spatial Scales

Figure 9.15 Muncie

Importance of scale in determining distribution patterns: At one scale pattern may be random, at another scale, might be uniform: At one scale pattern may be random, at another scale, might be uniform:

Distribution of Tropical Bee Colonies Hubbell and Johnson predicted aggressive bee colonies have regular distributions; Hubbell and Johnson predicted aggressive bee colonies have regular distributions; Predicted non-aggressive species have random or clumped distributions Predicted non-aggressive species have random or clumped distributions

Hubbell and Johnson results: 4 species with regular distributions were highly aggressive 4 species with regular distributions were highly aggressive Fifth non-aggressive and randomly distributed Fifth non-aggressive and randomly distributed

Figure 9.11

What causes overall pattern? Behavior! Behavior! Aggressive bees were uniformly spaced due largely to their interactions. Aggressive bees were uniformly spaced due largely to their interactions. Non-aggressive species were random - did not interact. Non-aggressive species were random - did not interact.

Figure 9.13

Density: The average number of individuals in a unit of space (area or volume). Density: The average number of individuals in a unit of space (area or volume). Characteristics of Populations: Density

Density: The average number of individuals in a unit of space (area or volume). Examples: Number of trees per acre Number of hawks per km 2 Number of clams per m 2 Number of algae cells per liter “Unit Area” Large for big organisms Small for small organisms Unit Volume For Aquatic Species

Determining Density: Sessile Organisms (Ex. plants) Randomly locate “representative” sample points (randomization & replication) Randomly locate “representative” sample points (randomization & replication) Establish “plots” of known area Establish “plots” of known area Count number of individuals in each plot Count number of individuals in each plot Average number of individuals per plot Average number of individuals per plot

Determining Density: Sessile Organisms (Ex. plants) Randomly locate “representative” sample points Randomly locate “representative” sample points Establish “plots” of known area Establish “plots” of known area Count number of individuals in each plot Count number of individuals in each plot Average number of individuals per plot Average number of individuals per plot Average number per plot Density =_____________________ Density =_____________________ Plot Area Plot Area

Example: Computing Density 1. Randomly locate 20 points in Christy Woods. 2. Establish a 10m x 10m square plot at each point. (Plot area = 100 m 2 = 0.01 hectare (1 ha = 10,000 m 2 ) (Plot area = 100 m 2 = 0.01 hectare (1 ha = 10,000 m 2 ) 3. Count the number of sugar maples in each plot. 4.Suppose average number of maples per plot = What is the density of sugar maple per hectare? Sugar Maple = 4.5 trees/plot = 450 maples / ha Density 0.01 ha/plot

Determining Density: Mobile Organisms Mark-Recapture Method Mark-Recapture Method –Obtain random sample of organisms, “mark” them and release them back to the population. –After a period of time, obtain another random sample of organisms. –Count the number of marked organisms in the second sample. Population = M (n + 1) Size (N) (m + 1) M n m

Example: Estimating Population Size from Mark-Recapture Number of animals marked in 1st sample M = 100 Number of animals marked in 1st sample M = 100 Total number of animals in 2nd sample n = 150 Total number of animals in 2nd sample n = 150 Number of marked animals in 2nd sample m = 11 Number of marked animals in 2nd sample m = 11 Population = M (n + 1) = 100 (151) = 1258 Size (N) (m + 1) 12 Note: N is not “density”, as there is no “unit space”.

Larger Species Tend to Have Lower Density Than Smaller Species. Why? Big organisms take-up more space. Example: More ants can fit into an acre than trees. Big organisms need more resources to live, requiring larger areas in which to obtain those resources. Big organisms tend to produce fewer, larger offspring. Small organisms tend to produce many small offspring.

Figure 9.21

Figure 9.20

Species Abundance and Risk of Extinction Local density within a habitat area: Small populations at higher risk. Local density within a habitat area: Small populations at higher risk.

Species Abundance and Risk of Extinction Local density within a habitat area: Small populations at higher risk Local density within a habitat area: Small populations at higher risk Habitat Tolerance: Number of habitat-types within a landscape where present (habitat specialists at higher risk) Habitat Tolerance: Number of habitat-types within a landscape where present (habitat specialists at higher risk)

Species Abundance and Risk of Extinction Local density within a habitat area: Small populations at higher risk. Local density within a habitat area: Small populations at higher risk. Habitat Tolerance: Number of habitat- types within a landscape where present (habitat specialists at higher risk). Habitat Tolerance: Number of habitat- types within a landscape where present (habitat specialists at higher risk). Large-scale geographic distribution: Species found in only one location at higher risk (“All the eggs in one basket”). Large-scale geographic distribution: Species found in only one location at higher risk (“All the eggs in one basket”).

Increasing vulnerability to extinctionIncreasingRarity Least vulnerable to extinction

Moderate vulnerability to extinction

High extinction

Highest extinction Other Example ?

The End