Presentation on theme: "Population Dynamics Evolution, Natural Selection, and Human Impacts for Introduction to Environmental Science."— Presentation transcript:
1 Population DynamicsEvolution, Natural Selection, and Human Impacts for Introduction to Environmental Science
2 Population LevelsPopulation 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 areaPopulation dispersion – spatial values of population including clumping, uniform, and random (see figure in text)
4 Age StructureThis is a breakdown of the major contributors to populations in ecosystemsPrereproductiveReproductivePostreproductiveThe 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?
9 Population StressesCarrying 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
11 This shows the growth of Japan and approach to meeting its carrying capacity. *Carrying Capacity:A Model with Logistically Varying Limits byPERRIN S. MEYER1 and JESSE H. AUSUBEL2 in Technological Forecasting and Social Change 61(3): , 1999.
12 Population StressesAny population growing exponentially goes through a “J” shaped growth, but most of the time environmental influences create an “S” shaped pattern in 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 DensityDensity – 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 CurvesPopulations could be stable, cyclic or irruptive due to various factorsPredation, 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 independentKStable environment, density dependent interactionssmall size of organismlarge size of organismenergy used to make each individual is lowenergy used to make each individual is highmany offspring are producedfew offspring are producedearly maturitylate maturity, often after a prolonged period of parental careshort life expectancylong life expectancyeach individual reproduces only onceindividuals can reproduce more than once in their lifetimemost of the individuals die within a short time but a few live much longermost individuals live to near the maximum life spanCourtesy 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; andIII 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 LifeTaxonomically, 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 EvolutionThe sum all genes in a population is called the gene poolA gene with two or more molecular forms is called an AlleleNew alleles are referred to as mutationsA 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 traitFitness differences a consistent relationship between that trait and some measure of reproductive successInheritance (consistent relationship) for that trait between parents and their offspring (at least partially independent of the environment)
31 Courtesy of http://facstaff.uww.edu/wentzl/modes.html
32 Three Types of Selection Stabilizing tends to eliminate individuals on the ends of a population without shifting the mean populationDirectional tends to shift allele frequency so that the mean genetic outcome changesDisruptive (Diversifying) favors individuals at the extremes and reduces the norm, but does not shift the mean genetic outcome
33 CoevolutionIf 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 EvolutionMicroevolution – works on a species levels with changes over timeMacroevolution goes beyond the species level and longer geological time periods.There are misconceptions about this theory… Fitness versus Fittest
36 SpeciesGeologically speaking the start of the Cenozoic Era (65 million years), started with 99% of all species on earth being extinct!Large scale continental movementGradual climate caused by shifting continentsRapid 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 predatorsIntroducing new speciesOverharvesting resourcesInterfering with geochemical cyclesGentically 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 Parasitism
44 Island Biogeography MacArthur and Wilson’s theory Larger Islands support more biodiversityIslands closer to the mainland also support more biodiversityIslands farther from the mainland support less biodiversity and sometimes smaller-sized species