Populations are individuals of a species that live in a particular habitat. Ecologists measure the characteristics of populations: size, density, and distribution pattern. Life tables are useful for calculating the life expectancies of individual population members. Survivorship curves show the number of individuals surviving at each age interval plotted versus time. Populations with unlimited resources grow exponentially—with an accelerating growth rate. When resources become limited, populations follow a logistic growth curve in which population size will decrease at the carrying capacity. Humans have increased their carrying capacity through technology, urbanization, and harnessing the energy of fossil fuels. Unchecked human population growth could have dire long-term effects on human welfare and Earth’s ecosystems. Communities include all the different species living in a given area. The variety of these species is referred to as biodiversity. Species may form symbiotic relationships such as commensalism, mutualism, or parasitism. Its foundation and keystone species describe community structure. Communities respond to environmental disturbances by succession: the predictable appearance of different types of plant species until a stable community structure is established.
OpenStax College. (2013). Concepts of biology. Retrieved from http://email@example.com. OpenStax CNX. Available under Creative Commons Attribution License 3.0 (CC BY 3.0). Modified from Original.