Ch. 8

Disruptions are part of daily life. A late bus or a locker jam may be disruptions you have encountered at school. How do disruptions, such as population changes, natural disasters, and human activity, impact ecosystems? What would happen to a forest ecosystem if all the hawks and owls disappeared? Population Changes Energy moves through food webs, in the form of food, every time an organism eats a living or dead organism. This energy transfer happens in predictable patterns. Food webs and their continuous flows of energy sustain the ecosystem. But when population sizes or species change in a food web, patterns of energy transfer are impacted. Causes of Population Changes There are four main factors that cause population changes in ecosystems. These factors affect the number of producers and consumers and the amount of available energy in a food web. Since all organisms in a food web depend on one another, changes to one population can affect the others. • Moving In When individuals move into a population from another area, the population increases in size. • Moving Out When individuals move out of a population to another area, the population decreases in size. • Birth Rate When births in a population rise or fall more than usual, the population size can increase or decrease. • Death Rate When deaths in a population rise or fall more than usual, the population size can decrease or increase. 4 main factors TEKS 8.12A, 8.5A, 8.5B, 8.5E, 8.5G

Effects of Population Changes When individuals move in or out of an ecosystem, or there are changes to birth or death rates, it is usually due to environmental changes. These may be changes to weather or climate conditions, or the amount of food, water, or space. Anytime a population changes, patterns of energy transfers in the food web also change. For example, predator-prey relationships can be disrupted. This means that organisms lose the organisms that hunt them, or lose their food source. Food Web Changes In the 1700s and 1800s, coats and hats made of sea otter fur were very popular. As a result, sea otters were hunted almost to extinction. That population change not only impacted sea otter prey, it impacted energy transfers throughout the food web. The arrows in the food web show how energy is transferred.

Sea otter Sea urchin Sea star Crabs Mussels Gull Detritus Kelp

1 Because of overhunting, sea otter populations dropped. Otters were basically removed from the food web. 2 Sea urchins lost their predator, the otter. The urchin population rose, and the population of their food, kelp, dropped sharply. 3 Sea stars lost their predator, otters. But their prey, mussels, dropped sharply because they ate kelp and their predators, gulls, remained. 4 Crabs lost one predator, but gulls remained. The crab food source, detritus (wastes and remains), was stable.

Effects of Natural Disasters Natural disasters, including floods, hurricanes, tornadoes, volcanoes, and wildfires, often impact, or change, the living and nonliving components in an ecosystem. If an organism no longer has access to things it needs for survival, such as food, water, and shelter, its population is affected. Natural disasters can cause the removal of populations, decreases in population size, or increases in population size because of reduced competition. Changes in the number and variety of populations can change the patterns of energy transfer in food webs and weaken them. Vocab Tip To impact something is to change it in some way. Consider events that could impact an ecosystem in positive ways or negative ways. Discuss your ideas with a partner. Impacts of Natural Disasters An uncontrolled wildfire can be a natural disaster. But lack of fire disrupts some ecosystems.

Negative Impacts Large wildfires can kill populations or destroy their food, water, or shelter resources. Populations that survive might have to move away. Positive Impacts Wildfires can help some ecosystems and populations. Jack pine tree seeds usually only grow when they have been in a fire. Kirtland's warbler, a rare North American bird species, only nests in jack pine forests where the trees are 5–16 feet tall. Kirtland's warbler and its whole ecosystem depend on regular fires.

406 ECOSYSTEMS AND POPULATION CHANGE Ecosystem Disruptions and Food Webs Copyright © Savvas Learning Company LLC. All Rights Reserved. Photo Credits: Sergio Azenha/Alamy Stock Photo; Agami Photo Agency/Shutterstock

Effects of Human Intervention An intervention is the act of interfering in a process in the hopes of improving a result. Not wearing otter fur coats and hats, planting trees after a wildfire, or protecting habitats are positive effects of human intervention. But not all human interventions have positive effects. Chemicals The use of chemicals such as fertilizers and pesticides, though it can improve some lives, can disrupt food webs. Fertilizers run off into bodies of water which feed overgrowths of algae. When the algae die, decomposers break them down and use all the oxygen. The lack of oxygen can kill fish and other organisms. Rodent poison kills birds of prey when they are poisoned by rodents they eat, and then there are fewer predators eating rodents. These population changes cause serious disruptions in transfers of energy in food webs. Introduction of Species Humans also intervene by introducing species into an ecosystem, either to solve a problem or by mistake. Invasive species, such as the kudzu plant, are non-native species that spread rapidly. They reduce consumers in food webs, crowd out native populations, and impact the transfer of energy in food webs. Invasive Species Kudzu’s fast-growing vine covers everything in its path. Kudzu is an invasive species in the U.S. From the 1930s to the 1950s, kudzu was promoted as a tool for preventing soil erosion. Now kudzu strangles native vines like honeysuckle, tree saplings, and even grows on power lines.

When volcanoes erupt, they create new rock. So how did the Hawaiian Islands, which were formed by volcanic activity, go from barren rock to becoming the home to over 25,000 unique species? The answers are succession and a lot of time. Primary Succession Primary succession is the series of changes that occurs on surfaces where no soil or organisms exist. It can occur after a natural event, such as a glacier or volcanic eruption, or as a result of a human activity, such as abandonment of a stone structure. Pioneer species, such as mosses and lichens, are the first species to colonize, or populate, an area. As they grow, they build soil. Soil is an essential first step to building a thriving ecosystem with diverse species and growing populations. Primary Succession After a volcanic eruption in a place like Hawaii, primary succession begins the process of building an ecosystem.

TEKS 8.12B, 8.5G

1 After a volcanic eruption, new rock forms from cooled lava. Pioneer species, such as lichen, begin to grow. A lichen is a symbiotic relationship between algae and fungi. 2 Lichens release acids that help turn rock into soil. When lichens die, decomposers break down the remains to make better soil. That allows plants such as ferns to grow. Insects and spiders move in. 3 Over time, as more organic material and soil build up, new species such as shrubs, trees, and other animals move into the area. 4 The resulting community is a stable ecosystem filled with a variety of species living together and relying on one another. 424 ECOSYSTEMS AND POPULATION CHANGE Ecological Succession Copyright © Savvas Learning Company LLC. All Rights Reserved.

Secondary Succession Secondary succession is the series of changes that occurs in an area where the ecosystem has been disturbed by natural events or human activity, but where soil and organisms still exist. Because these areas previously supported life, succession restarts from existing soil and seeds, roots, or young left by organisms that died. At the beginning of secondary succession, the variety of species is often low. As food webs rebuild over time, the number of species increases. Secondary succession can occur as a result of natural events such as natural wildfires, widespread floods, tsunamis, hurricanes, tornadoes, and other events. Any event that destroys part of an ecosystem but leaves other parts alive can begin secondary succession. Secondary succession can also occur following human activities such as accidental wildfires; abandonment of fields, lots, and other properties; and logging. Secondary succession can begin anyplace humans have cleared mature plants and then left. Use Visuals Examine the diagram and read the caption and callouts. Have you ever seen secondary succession in your community? In a small group, discuss your observations and why you think they demonstrate secondary succession. Express your ideas clearly as you participate in the discussion. Secondary Succession Not all secondary succession begins with a disaster. Secondary succession can begin in an abandoned hayfield or an abandoned used-car lot.

1 Plant life from the areas surrounding an abandoned hayfield colonize the area. Native grasses and wildflowers grow quickly and produce many seeds. 2 Pine seedlings often grow in sparsely wooded areas because their seeds favor disturbed soil and strong sunlight. Pine trees eventually shade out many of the earlier plants. 3 Pine seeds cannot grow in shade. Seeds from hardwood trees, such as oak and hickory, grow in the shade of the mature pines. Over time, as hardwood trees shade out pine trees, the result is a stable hardwood forest. Ecological Succession ECOSYSTEMS AND POPULATION CHANGE 425

Think of the last park you went to. How many different species did you see? The health of an ecosystem and its organisms relies on the variety of species in it. But why is that so important? Stability and Sustainability Biodiversity is the number and variety of different species in an area and the variations within species. The area could be as large as Earth or smaller than the park you visited. Certain species are essential to the health of the ecosystem. Species, like bees, that are essential to the health of many other organisms in an ecosystem are keystone species. All the species in an ecosystem are connected to one another. A change that affects one species can affect the health of all the others. Biodiversity includes genetic, species, and ecosystem diversity. Ecosystems with greater biodiversity tend to have greater stability, which means the ecosystem can withstand disruptions from natural and human causes. If an ecosystem is stable, that contributes to its sustainability, or its ability to maintain balance over time. This means the ecosystem can provide the resources needed for organisms to stay healthy. Pollinators Bees and other pollinators are keystone species. Pollinators bring pollen to flowering plants, allowing the plants to reproduce. Animals that get energy from plants, directly or indirectly, depend on pollinators to help them stay healthy. TEKS 8.12C, 8.5D, 8.5G

Genetic diversity The genetic diversity in an ecosystem describes the differences in genetic information among individuals of a population or species. Genetic diversity allows for variations and adaptations. The greater its genetic diversity, the more likely it is that a species can adapt and survive. Species with low genetic diversity lack the ability to adapt to changing environmental conditions. Species diversity The number or variety of species within a given area is known as species diversity. As new species are discovered, species diversity increases. When all members of a species disappear from Earth, or become extinct, species diversity decreases. This can happen when environmental conditions change and species cannot adapt to the change. Ecosystem diversity The number and variety of Earth’s ecosystems make up ecosystem diversity. The more ecosystems Earth has, and the more variety they have, the more ecosystem diversity Earth has. You saw this diagram before when you learned how food webs can be disrupted. With a partner, discuss how disruptions could lead to a decrease in biodiversity in the kelp forest ecosystem. Use Visuals Population Changes Loss of biodiversity in the kelp forest ecosystem after sea otters declined showed that they are a keystone species.

Sea otter Sea urchin Sea star Crabs Mussels Gull Detritus Kelp

1 Sea otters are a keystone species and are predators. In addition to other marine invertebrates, otters eat larger sea urchins from the kelp forest. Otters help sustain the ecosystem by keeping a stable sea urchin population. 2 If the sea urchin population increased, urchins would eat too much kelp. This would affect the health of other species that ate kelp. The biodiversity of the kelp forest ecosystem would decrease without otters. 3 The sea star’s population affects the population of most other species, either directly or indirectly. 4 Crabs eat detritus – wastes, remains, and bits of food. Their population is stable when other species in the food web are stable. Biodiversity ECOSYSTEMS AND POPULATION CHANGE 441 Copyright © Savvas Learning Company LLC. All Rights Reserved.

Vocab Tip Think of the things you require, or need, to be happy. It could be getting enough sleep, seeing your friends, or doing a favorite activity. What factors do you think other organisms require? Health of Organisms There is an interdependence between the organisms and the function of an ecosystem. Biodiversity sustains the health of individual organisms. Biodiversity allows for a higher variety and quantity of the biotic and abiotic resources organisms need to survive. Biodiversity includes many producers, which support stable food webs. Biodiversity also allows for multiple predator-prey relationships and multiple roles for organisms, making food webs more flexible and allowing abiotic and biotic resources to be used sustainably. When the biodiversity of an ecosystem decreases, it does not function properly. Organism health can suffer because there are fewer resources for food, water, space, and other factors organisms require. Biodiversity and Healthy Organisms All organisms need water to stay healthy. An ecosystem with biodiversity functions to ensure sustainable use of resources such as water, since not all organisms use the same amount at the same place in the same way.

Primary succession is the series of changes that occurs on surfaces where no soil or organisms exist. It begins after events like volcanic eruptions, where pioneer species such as mosses and lichens colonize the area, gradually building soil. Secondary succession occurs in areas where an ecosystem has been disturbed (e.g., by wildfires or human activities), but soil and some organisms remain. This allows succession to restart more quickly.

Biodiversity refers to the variety of different species in an area. Keystone species, like bees, are crucial for the health of an ecosystem, influencing many other organisms. Genetic diversity describes the differences in genetic information among individuals of a population, allowing for variations and adaptations. Species diversity is the number or variety of species within an area, while ecosystem diversity encompasses the number and variety of Earth’s ecosystems.