2012 John Wiley & Sons, Inc. All rights reserved. Population Ecology A population is a group of individuals of a single species living in the same general area Population Ecology = study of how population size of a species changes over time and space Due to biotic and abiotic interactions 2012 John Wiley & Sons, Inc. All rights reserved. Population Density v. Size Population size = number of individuals Population density = number of individuals in a given unit of space (area or volume). Ex: minnows per Liter of pond water A B 2012 John Wiley & Sons, Inc. All rights reserved. Calculating Population Change r = (b d) + (i e) 2012 John Wiley & Sons, Inc. All rights reserved. r = intrinsic rate of increase = the rate at which a population increases in size if there are no limitations on population growth r = per capita rate of increase = increase in population size (number of offspring that survive to reproduce) Biotic potential 2012 John Wiley & Sons, Inc. All rights reserved. Exponential Growth Intrinsic Rate of Growth (Biotic Potential) Growth rate under ideal conditionsno limits Expansion into new habitat, re-colonization post-disturbance, rebound after population decline Limited time span J- Shaped Curve (exponential growth) 2012 John Wiley & Sons, Inc. All rights reserved. Environmental Resistance Environmental limits (resistance) Prevent indefinite reproduction Density dependent factors Carrying Capacity (K) Maximum # of individuals an environment can support Can change over time Causes S- shaped curve (logistic population growth) resistance 2012 John Wiley & Sons, Inc. All rights reserved. Carrying capacity (K) is the maximum population size the environment can support Carrying capacity varies with the abundance of limiting resources which can change over time 2012 John Wiley & Sons, Inc. All rights reserved. Environmental Resistance Environmental limits (resistance) Prevent indefinite reproduction Unfavorable food, water, shelter, predation, etc. Carrying Capacity (K) Maximum # of individuals an environment can support Causes leveling off of exponential growth S- shaped curve of logistic population growth 2012 John Wiley & Sons, Inc. All rights reserved. Factors That Affect Population Size Density Dependent Factor Factor whose effect on population changes as population density changes Examples: Predation Disease/parasitism Competition (for limited resources) Waste accumulation Intrinsic physiologic factors 2012 John Wiley & Sons, Inc. All rights reserved. Figure Competition for resources Territoriality Intrinsic factors Disease Predation Toxic wastes 5 m 2012 John Wiley & Sons, Inc. All rights reserved. Figure , Time (days) (a) A Paramecium population in the lab (b) A Daphnia population in the lab Time (days) Number of Daphnia/50 mL Number of Paramecium/mL 2012 John Wiley & Sons, Inc. All rights reserved. Boom-Or-Bust Population Cycles 2012 John Wiley & Sons, Inc. All rights reserved. Factors That Affect Population Size Density Independent Factors Factors that affects population size, but is not influenced by changes in population density Examples: Killing frost Severe blizzard Fire Landslide/avalanch flooding 2012 John Wiley & Sons, Inc. All rights reserved. Evolution and Life History Diversity A life history entails three main variables The age at which reproduction begins How often the organism reproduces How many offspring are produced per reproductive episode 2012 John Wiley & Sons, Inc. All rights reserved. Semelparity--big-bang reproduction--reproduce once and die Unpredictable environments Probability of adult survival, low Relatively low parental investment in offspring Iteroparity--repeat reproduction--produce offspring repeatedly Predictable environments Probability of adult survival high Relatively high parental investment in offspring. 2012 John Wiley & Sons, Inc. All rights reserved. Life History Strategies are trade-offs Resources are finite: Adult survival v. reproductive output High output; low investment v. low output; high investment r v. K 2012 John Wiley & Sons, Inc. All rights reserved. K-selection, or density-dependent selection, selects for life history traits that are sensitive to population density r-selection, or density-independent selection, selects for life history traits that maximize reproduction 2012 John Wiley & Sons, Inc. All rights reserved. Reproductive Strategies r-selected speciesK-selected species - Smaller body size - Early maturity - Short life span - Large broods (# of offspring each reproductive event) - Little or no parental care - Probability of long term survival is low - e.g., Mosquitoes, Dandelions, - Larger body size - Slow development - Late reproduction - Long life span - Small broods (# of offspring each reproductive event) - Significant often prolonged parental care - Low reproductive rate - e.g., Redwood trees, elephants, human beings 2012 John Wiley & Sons, Inc. All rights reserved. Figure 53.6 I Percentage of maximum life span Number of survivors (log scale) , II III 2012 John Wiley & Sons, Inc. All rights reserved. Survivorship curves can be classified into three general types Type I: Low death rates during early and middle life and an increase in death rates among older age groups Type II: A constant death rate over the organisms life span Type III: High death rates for the young and a lower death rate for survivors Many species are intermediate to these curves 2012 John Wiley & Sons, Inc. All rights reserved. Survivorship