Predation Douglas Wilkin, Ph.D. Jean Brainard, Ph.D.
Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required)
To access a customizable version of this book, as well as other interactive content, visit www.ck12.org
CK-12 Foundation is a non-profit organization with a mission to reduce the cost of textbook materials for the K-12 market both in the U.S. and worldwide. Using an open-content, web-based collaborative model termed the FlexBook®, CK-12 intends to pioneer the generation and distribution of high-quality educational content that will serve both as core text as well as provide an adaptive environment for learning, powered through the FlexBook Platform®. Copyright © 2013 CK-12 Foundation, www.ck12.org The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws. Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms. Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Commons from time to time (the “CC License”), which is incorporated herein by this reference. Complete terms can be found at http://www.ck12.org/terms. Printed: October 29, 2013
AUTHORS Douglas Wilkin, Ph.D. Jean Brainard, Ph.D.
www.ck12.org
C ONCEPT
Concept 1. Predation
1
Predation
• Describe predation and its effects on population size and evolution.
What may be the most common way different species interact? Biomes as different as deserts and wetlands share something very important. All biomes have populations of interacting species. Species interact in the same basic ways in all biomes. For example, all biomes have some species that prey on others for food.
Predation
Predation is a relationship in which members of one species (the predator) consume members of another species (the prey). The lions and buffalo in Figure 1.1 are classic examples of predators and prey. In addition to the lions, there is another predator in this figure. Can you spot it? The other predator is the buffalo. Like the lion, it consumes prey species, in this case species of grass. However, unlike the lions, the buffalo does not kill its prey. Predator-prey relationships such as these account for most energy transfers in food chains and food webs.
Predation and Population
A predator-prey relationship tends to keep the populations of both species in balance. This is shown by the graph in Figure 1.2. As the prey population increases, there is more food for predators. So, after a slight lag, the predator population increases as well. As the number of predators increases, more prey are captured. As a result, the prey population starts to decrease. What happens to the predator population then? 1
www.ck12.org
FIGURE 1.1 Predators and Their Prey. Two lions feed on the carcass of a South African cape buffalo.
FIGURE 1.2 Predator-Prey Population Dynamics. As the prey population increases, why does the predator population also increase?
Keystone Species
Some predator species are known as keystone species. A keystone species is one that plays an especially important role in its community. Major changes in the numbers of a keystone species affect the populations of many other species in the community. For example, some sea star species are keystone species in coral reef communities. The sea stars prey on mussels and sea urchins, which have no other natural predators. If sea stars were removed from a 2
www.ck12.org
Concept 1. Predation
coral reef community, mussel and sea urchin populations would have explosive growth. This, in turn, would drive out most other species. In the end, the coral reef community would be destroyed.
Adaptations to Predation
Both predators and prey have adaptations to predation that evolve through natural selection. Predator adaptations help them capture prey. Prey adaptations help them avoid predators. A common adaptation in both predator and prey is camouflage. Several examples are shown in Figure 1.3. Camouflage in prey helps them hide from predators. Camouflage in predators helps them sneak up on prey.
FIGURE 1.3 Camouflage in Predator and Prey Species. Can you see the crab in the photo on the left? It is camouflaged with algae. The preying mantis in the middle photo looks just like the dead leaves in the background. Can you tell where one zebra ends and another one begins? This may confuse a predator and give the zebras a chance to run away.
Summary
• Predation is a relationship in which members of one species (the predator) consume members of another species (the prey). • A predator-prey relationship keeps the populations of both species in balance.
Practice
Use this resource to answer the questions that follow. • http://www.hippocampus.org/Biology → Biology for AP* → Search: Ecological Interactions 1. 2. 3. 4.
Define intraspecific competition. Describe predator-prey interactions. What is mimicry? Give an example. Give an example of an example of camouflage. 3
www.ck12.org Review
1. Describe the relationship between a predator population and the population of its prey. 2. What is a keystone species? Give an example.
References 1. Luca Galuzzi - www.galuzzi.it. . CC-BY-SA 2.5 2. CK-12 Foundation. . CC-BY-NC-SA 3.0 3. Crab: Mila Zinkova; Mantis: Adrian Pingstone; Zebra: Pharaoh Hound, Fir0002. . Crab: CC-BY-SA 3.0; Mantis: Public Domain; Zebra: CC-BY 2.5
4