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

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Presentation on theme: "Population Dynamics Evolution, Natural Selection, and Human Impacts for Introduction to Environmental Science."— Presentation transcript:

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

2 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)

3 Individual to Population

4 Age Structure This is a breakdown of the major contributors to populations in ecosystems Prereproductive Reproductive Postreproductive The population growth rate swings based upon biotic and abiotic factors leading to growth or decline

5 Response to stress Populations change = (births + immigration) –
(deaths + emigration) A balance is considered Zero Population Growth (ZPG) What are the implications of ZPG?

6 Courtesy:

7 Courtesy:

8 Data from J. Kimbell, 2006, Biology

9 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

10 How Much Can we Hold?

11 This shows the growth of Japan and approach to meeting its carrying capacity.
*Carrying Capacity:A Model with Logistically Varying Limits by PERRIN S. MEYER1 and JESSE H. AUSUBEL2 in Technological Forecasting and Social Change 61(3): , 1999.

12 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


14 Carrying Capacity and J shaped growth

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

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

17 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.

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

19 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.


21 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

22 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…)

23 r- and K- selected Organisms
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

24 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

25 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


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

28 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.

29 Evolution, Adaptation, and Natural Selection http://www. mhhe
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

30 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)

31 Courtesy of

32 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

33 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.


35 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

36 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

37 Mass Extinction Epochs in Millions of Years Ago

38 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

39 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

40 Species Interactions Symbiotic Relationships Mutualism Commensalism


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


44 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

45 Island Biogeography

46 Island Biogeography

47 Island Biogeography

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