ECOLOGY

LESSON 10: SPECIES AND POPULATIONS World population from 500CE to 2150, based on UN (2004) [1]  projections and U.S. census information [2] , which are both applications of demography. No matter how much data is collected, unknown variables remain, so there are alternate possiblities for the future world population. Species and populations are probably the two most commonly used ecology terms, but they are often difficult concepts to grasp. Throughout this chapter, they will be discussed in detail, expanding on the definitions from previous chapters and explaining why there are no universally acceptable definitions. Factors influencing population growth and ways to measure and predict population growth will also be subjects of specific focus. Populations can be affected by so many factors that it is almost impossible to take every variable into account. Demography is the statistical study of the age structure of a population, and it can be used in research to determine...

 LESSON 9: SPECIES RICHNESS AND DIVERSITY Species Diversity Introduction Species Richness  ( s ) is a relative term that refers to the number of species in a community, and is directly associated with measuring the diversity of species in a given area. A related term, evenness (E), is another dimension of diversity that defines the number of individuals from each species in the same area. Together, these terms have been used to describe species diversity patterns on Earth. There are several hypotheses that have been proposed to explain species diversity patterns. Many of these hypotheses are based upon the idea that species are more diverse near the equator than near the poles. In other words, there is a recognized latitudinal gradient of species diversity on Earth. The hypotheses that support this latitudinal gradient can be divided into two groups: abiotic and biotic. The  biotic  hypotheses are those that explain species diversity patterns with relation to...

LESSON 8: INVASIVE SPECIES "Invasive species"—they may not sound very threatening, but these invaders, large and small, have devastating effects on wildlife. Invasive species are among the leading threats to native wildlife. Approximately 42 percent of threatened or  endangered species  are at risk due to invasive species. Human health and economies are also at risk from invasive species. The impacts of invasive species on our natural ecosystems and economy cost billions of dollars each year. Many of our commercial, agricultural, and recreational activities depend on healthy native ecosystems. What Makes a Species "Invasive"? An invasive species can be any kind of living organism—an amphibian (like the cane toad), plant, insect, fish, fungus, bacteria, or even an organism’s seeds or eggs—that is not native to an ecosystem and causes harm. They can harm the environment, the economy, or even human health. Species that grow and reproduce quickly, and spread...

LESSON 7:COMMUNITY SUCCESION AND STABILITY Key points Succession  is a series of progressive changes in the composition of an ecological community over time. In  primary succession , newly exposed or newly formed rock is colonized by living things for the first time. In  secondary succession , an area previously occupied by living things is  disturbed —disrupted—then recolonized following the disturbance. Introduction Have you ever looked at a landscape with a complex, diverse community of plants and animals—such as a forest—and wondered how it came to be? Once upon a time, that land must have been empty rock, yet today, it supports a rich ecological  community  consisting of populations of different species that live together and interact with one another. Odds are, that didn't happen overnight! Ecologists have a strong interest in understanding how communities form and change over time. In fact, they have spent a lot of...