Chapter 22 - The Basics of Ecology

The last unit of AP Biology integrates what you've studied throughout the year into a discussion of ecology. * This unit requires you to understand how organisms use energy and matter, as well as how energy moves across ecosystems. * The availability (or lack thereof) of energy in an ecosystem can decide its life or extinction. * Ecosystems must be able to adapt to changes in their surroundings. * @@Communication between organisms is vital because it allows them to adapt to changes in their surroundings.@@
These reactions can result in population shifts and population evolution. * This chapter will begin by discussing how organisms adapt to changes in their environment, followed by a discussion of energy flow across ecosystems. * The capacity of organisms to adjust to changes in their environment is frequently critical to their survival. * Behavioral or physiological strategies can be used by organisms to respond to environmental changes.
A stimulus is a change in the environment that causes a response. * A variation in day duration is one example of a stimulus that might elicit a reaction. * Some birds migrate in reaction to variations in day duration, which is a behavioral response.
Other species may reduce their metabolism to preserve energy in reaction to variations in day duration, which is a physiological response.
Some sensations are transmitted between species. * In reaction to changes in their environment, organisms transmit messages to one another. * These messages have the potential to alter the behavior of other creatures. * This communication among organisms can take place in a variety of ways.
^^Birds utilize audio signals to communicate with other birds and to attract mates. Some primates employ vocalizations to exert dominance or to alert predators of their presence. Chemical signals.^^ * Pheromones are chemical signals that some plants and animals emit in order to elicit a reaction from other species. * Skunks expel stinky compounds to frighten away possible predators. * Female insects emit compounds that male insects of the same species can detect. * Signaling among organisms can assist them in finding mates, establishing social hierarchies, and locating vital resources.
Natural selection will favor signals and reactions that enhance the likelihood of survival and successful reproduction. * This selection can cause population shifts and evolution throughout time. * Individuals and groups can benefit from cooperative activities. * Energy is used by organisms to grow, reproduce, and maintain their order. * Adaptations for maintaining energy levels and body temperatures differ between animals.
Endotherms utilise thermal energy created by their metabolism to keep their bodies warm. * Endotherms include mammals and birds. * Ectotherms lack internal processes for maintaining body temperature and therefore rely on their surroundings for heat. * To control their body temperature, they must alter their habits. * If a lizard's body temperature falls, it will crawl to a heated rock or into the sunlight to warm up.
One explanation for this is because smaller organisms have a higher surface area-to-volume ratio and hence lose more heat to their surroundings. * %%Smaller animals require greater metabolic rates to compensate for this heat loss.%% * Access to energy is critical to an organism's health. * Organisms are continually consuming energy in order to exist, and they get energy from the food they consume (or the carbon-containing molecules they produce if the organism is photosynthetic). * A net gain in energy might result in energy storage (such as in animal fat cells) or organism development. * A net loss of energy might lead to mass loss or even death of the organism.
Fluctuations in energy availability in an ecosystem, such as a decrease in sunshine or the number of producers, can lead to population size changes. * If energy becomes less available in an environment (for example, if a massive building lowers the quantity of sunshine available), the ecology suffers. * Photoautotrophs are plants. * Chemoautotrophs derive their energy from tiny inorganic compounds in their surroundings. * The majority of chemoautotrophs are bacteria found in harsh conditions such as deep-sea thermal vents or geothermal geysers.
Heterotrophs obtain their energy from carbon molecules produced by other species. * Heterotrophs can derive energy from carbohydrates, lipids, or proteins by using hydrolysis processes to break down these macromolecules. * Heterotrophs are animals. * Decomposers decompose dead organic matter, allowing nutrients from deceased species to be recycled through ecosystems.
Many fungus and bacteria degrade organic matter. * Detritivores are creatures that get their energy from the organic waste of deceased plants and animals. * Detritivores include millipedes, centipedes, and earthworms. * Decomposers and detritivores both play key roles in nutrient cycling in ecosystems.
Some species use unconventional energy-gathering tactics. * Kleptoplasty is shown by a few number of species. * Kleptoplasty occurs when a heterotroph consumes an autotroph for nourishment while removing the chloroplasts from the autotroph's cells and incorporating them into its own cells.
The sea slug Elysia crispata feeds on algae and integrates chloroplasts (from the algae it eats) into its own cells. * When the sea slug is unable to obtain food, it moves into the sunshine. * The quantity of biomass in the lower trophic levels of a food chain grows as you proceed down the trophic levels, with the producers having the most biomass.
If the producers' population number decreases, there may not be enough food or energy for the other trophic levels, and the food chain may collapse. * This is referred to as ecological bottom-up control. * Many marine ecosystems' bottom trophic level is photosynthetic phytoplankton. Zooplankton consume phytoplankton, and sea stars, fish, and even whales consume zooplankton.
Herbicide runoff can contaminate the water, lowering the amount of phytoplankton. * This can lead to a decrease in the size of the zooplankton population as well as the animals that rely on zooplankton for food. * Animals at higher trophic levels may aid in population control at lower levels. * When apex predators are gone from an ecosystem, the population numbers of other predators decrease.
Venezuela's rain forests provide an example of top-down control. * Dam building produced isolated rain forest islands, some of which housed top predators such as crocodiles, while others were left without top predators. * After a few years, the biodiversity of rain forest parts lacking top predators was severely decreased (with fewer saplings, trees, and other plants).
Plant-eating animal populations expanded rapidly in the absence of crocodiles, lowering the quantity of plants in these places. * As a result, the species that rely on these trees and plants have fewer habitats. * $Crocodiles would consume some of the creatures that graze on seeds and plants on rain forest islands with top predators, decreasing the population of these animals and protecting the number of plant species in these locations.$ * Food availability and the energy it offers organisms influence their reproductive strategy. * In response to energy availability, different species employ various reproduction methods. * Organisms that dwell in unstable habitats (with limited availability to energy-containing chemicals) will generate a high number of progeny at once. * Because there is less availability.