ENVH 4387/53871 Principles of Microbial Ecology Lecture Topic Number 2 Population Dynamics ENVH 4387/5387 Biological Analysis

ENVH 4387/53872 Introduction l We will understand the factors that affect population size l We are primarily interested in how pollutants will affect population size

ENVH 4387/53873 Introduction l Four measures can be used to determine the impact of the many factors tat affect population size n birth rates n death rates n gains from immigration n losses from emigration

ENVH 4387/53874 Carrying Capacity (K) l The maximum number of populations or individuals that a habitat can support throughout the complete life cycle

ENVH 4387/53875 Competition l The struggle for limited resources (e.g., nutrients) among and between populations within a community l Density-dependent n critical threshold of population size

ENVH 4387/53876 Logistic Equation l Describes populations that grow in a sigmoidal (S-shaped) fashion l Useful in predicting future population size l Useful in understanding factor(s) that affect population size by documenting changes in the equation results

ENVH 4387/53877 Logistic Equation l dN/dt = rN(1-N/K) –N=population size –t = time –r = rate of population growth –K = carrying capacity

ENVH 4387/53878 Logistic Equation l Assumptions n population growth is not unlimited (i.e., some finite population size exists) n the speed a population approaches the maximum size is determined only by the rate of growth n the effective rate of growth [rN(1-N/K)] is density dependent

ENVH 4387/53879 Factors that Affect Population l Competition n between or within species –for resources and nesting sites n interactions between species –predation –parasitism n effects of the abiotic environment –temperature –salinity –drought vs. flood

ENVH 4387/ Colonizing Strategies l Different species are adapted to survive in different ways n different needs for resources n different types of life cycle n react to changes in different ways

ENVH 4387/ r-Strategists l successful colonizers l continually invade new temporary habitats l high rates of increase l high migratory ability l poor competitive ability

ENVH 4387/ k-Strategists l stable habitats l maximize use of available resources l maximize size of population l tend to remain at equilibrium n long lived individuals n low reproductive rates l high competitive ability

ENVH 4387/ Abiotic Factors l Temperature l Salinity l Water l Pressure l pH l Oxygen

ENVH 4387/ Temperature l Temperature n Q 10 describes the change in reaction rate that occurs when the temperature is increased by 10°C n rule of thumb - metabolic rate doubles with every 10°C increase in temperature n growth rate generally follows metabolic rate

ENVH 4387/ Temperature l Optimal growth temp. maximum growth rate l Stereothermophiles - grow only at temperatures near their optimal growth temp. l Eurothermal - grow over a wide range of temperatures l Psychrophiles - cold loving grow best at temperatures just above freezing l Thermophiles - heat loving, grow optimally between 50°C and 70°C, usually survive above 100°C

ENVH 4387/ Temperature l Mesophiles - most soil or aquatic microorganisms are mesophilic l range is 15°C - 35° for saprophytic mesophiles; optimal temperature is 25°C l range is 15°C - 44°C for pathogenic mesophiles; optimal temperature is 37°C

ENVH 4387/ Salt l Some microorganisms living in the sea are unable to grow in freshwater l Some microorganisms living in freshwater are unable to grow in the sea l We call marine microorganisms - halophiles n salt concentration of 1.8% to 80%

ENVH 4387/ Salt l non-halophiles are the freshwater and soil microorganisms n salt concentration of % l extreme halophiles - live in saturated salt and areas such as the dead sea n salt concentration 4% to 100%

ENVH 4387/ Oxygen l Areobes - require the presence of oxygen to grow l Anaerobes - require the absence of oxygen to grow l Facultative anaerobes - grow optimally under aerobic conditions (presence of oxygen) but can grow under anearobic conditions

ENVH 4387/ Typical Number of Microorganisms in Various Ecosystems