Population Dynamics

Evolution, Natural Selection, and Human Impacts for Introduction to Environmental Science

Population Levels

Population Density – is the number of individuals of a population at a given time.

Ecological Population Density – the number of individuals (n) per unit of habitat area

Population dispersion – spatial values of population including clumping, uniform, and random (see figure in text)

Individual to Population

Age Structure

This is a breakdown of the major contributors to populations in ecosystems Prereproductive Reproductive PostreproductiveThe population growth rate swings based

upon biotic and abiotic factors leading to growth or decline

Response to stress

Populations change = (births + immigration) –

(deaths + emigration)

A balance is considered Zero Population Growth (ZPG)

What are the implications of ZPG?

Courtesy: www.globalchange.umich.edu

Courtesy: www.globalchange.umich.edu

Data from J. Kimbell, 2006, Biology

Population Stresses

Carrying capacity (K) is defined as the number of individuals of a given species that can be sustained indefinitely – spatially.

Population could grow exponentially with unlimited resources considered its maximum rate ( r) with unlimited biotic or reproductive potential

How Much Can we Hold?

*Carrying Capacity:A Model with Logistically Varying Limits by PERRIN S. MEYER1 and JESSE H. AUSUBEL2 in Technological Forecasting and Social Change 61(3):209-214, 1999.

This shows the growth of Japan and approach to meeting its carrying capacity.

Population Stresses

Any population growing exponentially goes through a “J” shaped growth, but most of the time environmental influences create an “S” shaped pattern in growth

Carrying Capacity and J shaped growth

Curve demonstrating the population of rabbits

*MIT System Dynamics in Education Project Under the Supervision of Dr. Jay W. Forrester by Leslie A. Martin

This shows exponential growth leading to overshoot and Population dieback of species like the reindeer in Alaska

Population Density Density – Dependent population

controls include competition for resources including predation, parasitism, and disease. Some more drastic controls include diseases like the Bubonic Plague in Europe in fourteenth century.

Density-Independent factors affect populations regardless of the size like natural disasters and use of chemicals (like pesticides causing cancers, etc…)

Population Curves

Populations could be stable, cyclic or irruptive due to various factors Predation, like the classic Lynx and

Snowshoe Hare demonstrate a classic predator-prey population curve in nature.

Reproductive Strategies

“r” strategists (Type III)- numerous offspring with a low survival rate to adulthood

- include many invertebrates and other animals that produce enough offspring to preserve their genetic variability

Reproductive Strategies

“K” strategists (Type I) - few offspring with high survivorship

includes a high degree of parental investment to insure offspring success

- examples include many mammals (i.e., humans, marine mammals, river otter, etc…)

r- and K- selected Organisms

r Unstable environment,

density independent

K Stable environment, density

dependent interactions small size of organism large size of organism

energy used to make each individual is low

energy used to make each individual is high

many offspring are produced few offspring are produced

early maturity late maturity, often after a prolonged period of parental

care

short life expectancy long life expectancy

each individual reproduces only once

individuals can reproduce more than once in their lifetime

most of the individuals die within a short time but a few live much

longer

most individuals live to near the maximum life span

Courtesy of www.bio.indiana.edu

Survivorship Curves

These curves demonstrate Late Loss Populations (K – strategists) Constant Loss Populations (K –

strategists) Early Loss Populations (usually r-

strategists)

These could be done regionally for human age population studies

Classic survivorship where I is a curve representing a Late loss population; II is a Constant loss like songbirds; and III is an Early loss curve like those that are r-strategists

posted by Bruce W. Grant, Department of Biology, Widener University, Chester, PA  19013

The Emergence of Life

Taxonomically, species have been identified and the process by which they have adapted (changes over a long period of time) are due to genetic variations and Natural Selection. Charles Darwin observed many ecological similarities and differences verses geographical location, which led to the Natural Selection theory. Selection is a process, complex system of stresses, that lead to adaptations.

Evolution, Adaptation, and Natural Selection http://www.mhhe.com/biosci/genbio/virtual_labs/BL_12/BL_12.html

Heritable Changes in population’s genetic makeup through successive generations is Evolution

The sum all genes in a population is called the gene pool

A gene with two or more molecular forms is called an Allele

New alleles are referred to as mutations A genetic trait that is that leads to survival

in environmental conditions is called an Adaptation

http://www.pbs.org/wgbh/evolution/library/01/5/quicktime/l_015_03.html

Natural Selection

This is a process in which a population has Variation among individuals in some attribute or

trait Fitness differences a consistent relationship

between that trait and some measure of reproductive success

Inheritance (consistent relationship) for that trait between parents and their offspring (at least partially independent of the environment)

http://www.pbs.org/wgbh/evolution/library/11/2/quicktime/e_s_4.html

Courtesy of http://facstaff.uww.edu/wentzl/modes.html

Three Types of Selection Stabilizing tends to eliminate

individuals on the ends of a population without shifting the mean population

Directional tends to shift allele frequency so that the mean genetic outcome changes

Disruptive (Diversifying) favors individuals at the extremes and reduces the norm, but does not shift the mean genetic outcome

Coevolution

If two different species interact over a long period of time, changes in the gene pool of one species will lead to changes in the gene pool of the second species.

www.indiana.edu/~curtweb/Research

Evolution

Microevolution – works on a species levels with changes over time

Macroevolution goes beyond the species level and longer geological time periods.

There are misconceptions about this theory… Fitness versus Fittest

Species

Geologically speaking the start of the Cenozoic Era (65 million years), started with 99% of all species on earth being extinct! Large scale continental movement Gradual climate caused by shifting

continents Rapid climate change caused by

catastrophic events (5 great ones) Major extinctions: 65, 180, 250, 345 and

500 million years ago

Mass Extinction Epochs in Millions of Years Ago

Human Impacts

Simplifying ecosystems Altering species control Eliminating predators Introducing new species Overharvesting resources Interfering with geochemical cycles Gentically modifying organisms,

thus affecting Selection pressures

Bobbi Low

“We haven’t evolved to be environmental altruists – but we can solve environmental problems”

We must work with, rather than against, our evolved tendencies.

Eliminate selfish genes

Species Interactions

Symbiotic Relationships

Mutualism

Commensalism

Parasitism

SEM of lichen: the linear fungal hyphae and the roundball-like algal groupings.

Island Biogeography

MacArthur and Wilson’s theory

Larger Islands support more biodiversity

Islands closer to the mainland also support more biodiversity

Islands farther from the mainland support less biodiversity and sometimes smaller-sized species

Island Biogeography

Island Biogeography

www.geog.ucsb.edu

Island Biogeography