Chapter 8: Population Dynamics, Carrying Capacity, and Conservation Biology 8-1 POPULATION DYNAMICS & CARRYING CAPACITY Population – all members of the same species living in a particular area POPULATION POPULATION NOT A POPULATION

Major Characteristics of Populations = POPULATION DYNAMICS Size – number of individuals Density – number of individuals in a certain space Dispersion - how they are spaced out across the range Age Distribution – the proportion of individuals at each age RANDOM UNIFORM CLUMPED

Factors Affecting Population Growth Birth and death rates Birth Rate > Death Rate  Growth Immigration and emigration Immigration > Emigration  Growth Population Change = (Births + Immigration) – (Deaths + Emigration)

Biotic Potential Biotic Potential = growth factors, capacity of a population for growth Intrinsic rate of increase (r) - rate at which a population would grow if it had unlimited resources Characteristics of populations with high biotic potential Reproduce early in life Have short generation times Can reproduce many times Produce many offspring each time they reproduce Limits to populations include shortage of… Light Water Space Nutrients

Environmental Resistance Environmental Resistance = decrease factors, all the factors acting jointly to limit the growth of a population Determine carrying capacity (K) – the number of individuals of a given species that can be sustained indefinitely in a given area Carrying capacity determined by interplay of biotic potential and environmental resistance

Biotic Potential vs. Environmental Resistance Growth Factors (Biotic Potential) Decrease Factors (Environmental Resistance) Abiotic Favorable light Favorable temperature Favorable chemical environment) Too much light or too little light Temperature too high or too low Unfavorable chemical environment Biotic High Reproductive rate Generalized niche Adequate food supply Suitable habitat Ability to compete for resources Ability to hide from or defend against predators Ability to resist diseases and parasites Ability to migrate and live in other habitats Ability to adapt to environmental change Low reproductive rate Specialized niche Inadequate food supply Unsuitable or destroyed habitat Too many competitors Insufficient ability to hide from or defend against predators Inability to resist diseases and parasites Inability to migrate and live in other habitats Inability to adapts to environmental change

Types of Population Growth Exponential Growth – unlimited growth of a population Occurs when population has food, space, protection from predation/disease, removal of waste products Each future generation will grow faster than the last Ex: bacteria

Types of Population Growth Logistical Growth – population grows, slows, and eventually reaches carrying capacity Phase 1 – exponential growth Phase 2 – slows down Due to: BR decreases, DR increases, immigration decrease, emigration increases Phase 3 – population stabilizes, reaches carrying capacity Carrying Capacity – maximum number of individuals than a particular environment can support

Factors Affecting Carrying Capacity Limiting Factors – factors that control the growth of a population Density Dependent Factors – factors that depend on the density of the population; control the populations and keep numbers in check Non-native species have a tendency to elude this and grow uncontrollably due to lack of natural predators, etc. Density Independent Factors – factors that do NOT depend on the density of the population; will affect all populations equally, regardless of their size

Density Dependent Factors Competition Fighting for space, food, water, sunlight, mates, etc. Can be within the same or different species Some will survive and reproduce, some will survive but NOT reproduce, some will die :0( Herbivory Predators to plant species Large loss of plant species may affect other primary consumers

Density Dependent Factors Predation Cyclic relationship (rise of one may induce the fall of the other; trend of rises and falls continues)

Density Dependent Factors Parasitism – feed at the expense of their hosts Ticks feeding on blood of dogs Disease – can cause a dramatic drop in a population due to infestation of a disease; decrease in one population may trigger a rise in another!

Density Dependent Factors Stress from Overcrowding – species fighting amongst themselves may lead to high levels of stress which may affect an organism’s ability to fight disease! Hmmmm….might explain why students get sick right before tests….maybe????

Density Independent Factors Weather Hurricanes, droughts, floods Natural Disasters wildfires 2004 Sri Lanka Tsunami

Density Independent Factors Sometimes “density-independent” factors do still depend slightly on population size Example: Increase in moose population after a drastic decrease in wolf population Cold winter with huge snowfall covered plants that moose feed on Island population  no chance for emigration Large population  more competition This density-independent factor may have affected a smaller population less

Population Change Curves in Nature 4 general types of population fluctuations: Stable – population size fluctuates slightly above and below carrying capacity Usually found in undisturbed areas or where there is little change in climate Irruptive – fairly stable populations that have a population explosion but then return to a lower size rather quickly Impacted by favorable weather, increase in food supply, decrease in predator

Population Change Curves in Nature 4 general types of population fluctuations: Chaotic Behavior – irregular changes in size with no real pattern seen Cyclic – changes occur in a pattern over a regular period of time Lynx and hare (10-year cycle)