Population Ecology

What is a population? A group of individuals of the same species occupying a given area Can be described by demographics Vital statistics such as size, density, distribution, and age structure

Some characteristics of populations Density and Distribution Number of individuals in some specified area of habitat Crude density information is more useful if combined with distribution data

Determining Population Size Direct counts are most accurate but seldom feasible Can sample an area, then extrapolate Capture-recapture method is used for mobile species

Assumptions in Capture-Recapture Marking has no effect on mortality Marking has no effect on likelihood to being captured There is no immigration or emigration between sampling times

Growth Rates of Populations Exponential growth Population size expands by ever increasing increments during successive intervals The larger the population gets, the more individuals there are to reproduce J curve

Growth Rates of Populations Logistic Growth As size of the population increases, rate of reproduction decreases When the population reaches carrying capacity, population growth ceases S curve Maximum number of individuals that can be sustained in a particular habitat

Growth Rates of Populations Overshooting Capacity Population may temporarily increase above carrying capacity Overshoot is usually followed by a crash; dramatic increase in deaths Boom and Bust Curve

Which of the following is a curve showing the growth rate of the human population? A. S curve B. J curve C. Boom and Bust Curve D. None of the above, humans are unique.

Factors that effect Population growth Limiting Factors Any resource that is in short supply Which determines the Carrying capacity of that population Maximum number of individuals that can be sustained in a particular habitat Can be Density dependent – factors that are effected by the population density Density independent – factors that are NOT affected by the populations

Density-Dependent Controls Logistic growth equation deals with density-dependent controls Limiting factors become more intense as population size increases Disease, competition, parasites, toxic effects of waste products

Density-Independent Controls Factors unaffected by population density Natural disasters or climate changes affect large and small populations alike

Which of the following is a density INdependent factor that will affect the population of deer in NJ? A. Tsunami B. Tick infections C. Cold winters D. Number of males in the population E. None of the above

How do different species interact with each other? SYMBIOSIS Parasitism Commensalism Mutualism

Change in the composition of species over time Succession Change in the composition of species over time

Pioneer Species Species that colonize barren habitats Lichens, small plants with brief life cycles Improve conditions for other species who then replace them

Types of Succession Primary succession - new environments Secondary succession - communities were destroyed or displaced

Primary Succession in Alaska’s Glacier Bay region Begins where nothing ever grew before Primary species are those that can withstand conditions like extreme heat, light, nutrient poor Soil Ex. Lichens, moss Fig. 40-18a, p.716

Fig. 40-18b, p.716

Fig. 40-18c, p.716

Fig. 40-18d, p.716

Fig. 40-31b, p.727

Secondary Succession Anything that decimates the landscape and succession must begin again. Ex. Volcanic erruptions, fire, floods, Clear cutting and human interference. Fig. 40-19a, p.717

Succession is rapid Soil is present and so are some seeds that withstood the calamity. Fig. 40-19b, p.717

Climax Community Stable array of species that persists relatively unchanged over time Succession does not always move predictably toward a specific climax community; other stable communities may persist