Chapter 8: Populations Population size, density & distribution

What is a population? Group of organisms of the same species interacting in the same area Also inter-breeding In natural populations, individuals can be… unitary = genetically unique modular = genetic clones Most animals are unitary while many plants, fungi, protists can be modular Modular plants are interconnected stems or clumps

Stolon – horizontal stem (above ground) that extends out to create a new individual clump Rhizome – root system that sprouts many individual clumps above ground

Examples of modular organisms Mint May-apple Coral

Distribution Distribution = spatial location, area over which it lives Influenced by habitat conditions & resource distribution

Distribution & geographic range If a given distribution includes the entire species, it is called the geographic range Ubiquitous = A species with a broad, widespread range made up of many populations Endemic = range is narrow containing few populations

Various levels of the distribution of a moss species Tetraphis pellucida

What is a meta-population? A group of populations that are connected by individuals who move back and forth among them

Population size & density Abundance = the total number of individuals in the population Density = number of individuals per unit area (also known as crude density)

Population Density Crude Density can be misleading, why? Not all individuals are uniformly distributed across the landscape Can be clumped around resources Can be randomly scattered by other forces Ecological density = number of individuals per unit of suitable habitat

Ecological Density in Bobwhite

3 patterns of spatial distribution

3 patterns of spatial distribution

3 patterns of spatial distribution

Determining Population Size Quadrat Sampling create a grid or squares on a landscape count individuals in each square multiply by number of squares on landscape can be affected by distribution pattern

Quadrat Sampling Results of quadrat sampling should always include a confidence factor based on distribution pattern

Determining Population Size Mark & Recapture capture and mark individuals release marked individuals back into population re-capture some and count marked individuals use ratios tom determine population size

Determining Population Size Indices of Abundance locate signs, sounds, evidence of individuals estimate number of individuals based on evidence Examples: Frog calls, bird calls, animal tracks, scat, trail cameras, etc…

Determining Population Size Which method should be used? Quadrat – sessile (non-mobile) organisms Mark & Recap. – mobile individuals Indices – elusive individuals in small numbers

What is dispersal? Dispersal = movement of individuals in space Immigration – individuals enter a population Emigration – individuals leave a population Immigration & Emigration = one-way trip Migration is a round-trip that occurs at a regular time interval Birds have an annual migration to warmer climate Plankton have a daily migration between deep and shallow water

What is Age Structure? Age Structure = the number or proportion of individuals in different age classes in a population 3 basic categories or age classes: pre-reproductive reproductive post-reproductive Age structure pyramid – graphical snapshot of the age structure of a population at some point in time

Age structure pyramids What is happening in each of these populations?

Age structure pyramids - prediction Shape of pyramid shows the growth pattern of the population: Pyramid shape with a broad base and narrow top for expanding populations (positive growth) Straight column with tapered top for stable populations (zero growth) Straight column that is “top-heavy” for declining populations (negative growth)

Chapter 10 Stuff K & r strategies

2 reproductive strategies Focus on one of the two main aspects of biotic potential: birth rate or recruitment rate Recruitment rate = % of offspring that reach reproductive age Both strategies work Not all organisms fit strictly into one category

r-selection Have tons of offspring but do not parent All energy is put into mass producing offspring Most young die, only one or two survive Smaller animals Useful for taking advantage of good conditions in a changing environment Short life cycles Insects, fish, etc…

K-selection Have few offspring but raise a high % to reach adulthood – parenting Put energy into raising young Most young survive, 1 or 2 out of a small brood Larger animals, high on food chain Longer life cycles / life spans Used by species that are highly adapted to cope with normal environmental changes Mammals, birds, people

Figure 9-9 Page 196 Carrying capacity K K species; experience K selection Number of individuals r species; experience r selection Time