Introduction to Ecology

Ecology A rigorous experimental science that requires a breadth of biological knowledge. Ecologists observe nature, generate hypotheses, manipulate environmental variables, and observe outcomes.

Biological Hierarchy Global ecology- the biosphere Landscape ecology-energy exchanges Ecosystem ecology-energy flow and chemical cycling Community ecology-interactions between species Population ecology-changes in population size Organismal ecology- organism’s structure, physiology and behavior

Earth’s Climate Influences The most significant influence on the distribution of organisms on Earth is climate Climate is composed of 4 abiotic factors Temperature Precipitation Sunlight Wind

Macroclimate Seasons are caused by variation in sunlight intensity

Latitudinal Variation in Sunlight

Global Air Circulation and Precipitation Intense solar radiation near the equation Warm moist air rises flows toward the poles releasing water Dry air descends at 30o north and south, absorbing moisture & rises again at 60o releasing precipitation Movement of air due to Earth’s rotation aids in creating the prevailing westerlies and the trade winds

Bodies of Water Ocean currents influence climates by heating or cooling overlying air masses Water’s high specific heat moderates climates of nearby land

Mountains Influence air flow and the amount of sunlight an area receives.

Terrestrial Biomes Biomes are characterized by vegetation type, latitude; mean temperature and precipitation . Named for a major physical or climatic feature and for predominant vegetation.

Major Land Biomes

Aquatic Biomes Determined by depth, flow, temperature, and chemistry of the overlying water. Photic zone- light for photosynthesis Aphotic zone- little to no light

What is Population Density? The number of individuals of the same species per unit area or volume i.e. the number of meerkats per square kilometer.

Species Distribution Distribution is a result of ecological and evolutionary interactions Dispersal – the movement of individuals from their area of origin Biotic factors – such as predation, herbivory, parasites, food resources.

Patterns of Dispersion Clumped Most common pattern Spend much of time in particular microenvironment Associated with mating behavior

Mark-recapture Method One method used by ecologist to calculate population densities Traps are set, captured animals are marked with tags then released After a period of time a second capture is done, researchers estimate numbers based on the yields of marked and unmarked individuals. Assumes equal probability of being trapped – Animals may be wary of traps if they were trapped once.

Counting It is possible to count all the individuals in a population to determine the size. Not practical Count the number of individuals (oak trees) in randomly selected plots Calculate the average density in the samples Extrapolate to estimate the population size Estimate density from some index of population size. Number of nests, tracks, etc.

Uniform Evenly spaced pattern of dispersion May result from direct interactions between individuals in population

Random Pattern of dispersion with unpredictable spacing Occurs in the absence of strong attractions or repulsions

Exponential & Logistc Growth Curves

Density dependent limiting factors Death rate rises, or birth rate falls as population density rises. Example of negative feedback regulation Includes Competition for resources Territory space Health Predation Toxic wastes Intrinsic factors

Density Independent Birth rate or death rate that does not change with population density. Physical factors kill a similar proportions of a local population regardless of its density. Natural disasters Human activity

Survivorship Curves Type I – high death rate in post reproductive years Type II – constant mortality throughout lifespan Type III- very high early mortality, but the few survivors live long (stay reproductive)

K- selected species vs. r-selected species Body Size Life Span # of Offspring Relative time of reproduction Survivorship Curve Growth Curve K-selected species Larger Low mortality Few offspring Late reproduction Type I s- shaped Logistic r-selected species Smaller High mortality Many offspring Early reproduction Type III Boom and bust Exponential growth

Factors that affect Population Size Abiotic Factors Sunlight & temperature Preciptation/ water Soil/ nutrients Biotic Factors Prey (food) Competitors Predators, parasites, disease Intrinsic factors Adaptations