APES Chapter 7

resilience

the ability of an ecosystem to be restored through secondary ecological succession after a severe disturbance.

Inertia/persistence

the ability of an ecosystem to survive moderate disturbances

Population size

the number of individual organisms in a population at a given time. Can change or stay the same in response to changing environmental conditions.

Minimum viable population

The smallest population size at which a species is able to sustain its numbers and survive.

Key Ideas of Chapter 7

1. Certain interactions among species affect their use of resources and their population sizes. 2. The species composition and population sizes of a community or ecosystem can change in response to changing environmental conditions through a process called ecological succession. 3. No population can escape natural limiting factors and grow indefinitely.

What are the three factors that affect how and at what rate ecological succession occurs?

1. Facilitation- one set of species makes an area suitable for species with different niche requirements, and often less suitable for itself (cause competition for space and whatnot). Ex: lichens and mosses build up soil allowing herbs and grasses to move in reducing space for mosses and lichens. 2. Inhibition- where some species hinder the establishment and growth of other species. Ex: Needles dropping off some pine trees makes the soil beneath the tree to acidic for most other plants to grow there. 3. Tolerance- where plants in the late stages of succession succeed because they are not in direct competition with other plants for key resources. Ex: Shade tolerant plants can live in shady forests because they do not need as much sunlight as the trees above them do.

Checkpoint for Understanding 7.1

1. Species have three options when competing directly with another species. A species that cannot compete may adapt, migrate, or go extinct. Explain how this is demonstrated in interspecific relationships. 2. A symbiotic relationship is defined as a close and long term relationships between two organisms. Identify the three types of symbiotic relationships. Explain why a predator prey relationship is not considered symbiotic.

7.2: How do Communities and Ecosystems Respond to Changing Environmental Conditions? Concept

1. The species composition of a community or ecosystem can change in response to changing environmental conditions through a process called ecological succession.

population density

A factor that can limit the sizes of some populations. The number of individuals in a population found within a defined area or volume. It is a measure of how crowded the members of a population are.

population

A group of interbreeding individuals of the same species.

predator

A member of one species that feeds directly on all or part of a member of another species.

Age structure

A population's distribution of individuals among various age groups (can have a strong effect on how rapidly a population grows or declines). Age groups are usually described in terms of organisms not mature enough to reproduce (the pre reproductive stage), those capable of reproduction (the reproductive stage), and those too old to reproduce (the post reproductive stage). The size of a population will likely increase if it is made up mostly of individuals in their reproductive stage, or soon to enter this stage. In contrast, the size of a population dominated by individuals in their post reproductive stage will tend to decrease over time.

Range of tolerance

A range of variations in a population's physical and chemical environment under which it can survive. Ex: A trout population may do best within a narrow band of temperatures, but a few individuals can survive above and below the trouts band of temps. Individuals within a population may also have slightly difference tolerance ranges for temperature, other physical factors, or chemical factors. These occur because of small differences in their genetic makeup, health, and age. Such differences allow for evolution through natural selection. The individuals that have a wider tolerance for change in some factor such as temperature are more likely to survive such a change and produce offspring that can tolerate it.

Commensalism

An interaction that benefits one species but has little, if any beneficial or harmful effect on the other. Ex: Birds make nest in trees, birds benefit, tree not harmed nor does it benefit

S shape curve

As a population approaches the carrying capacity of its habitat, the J- shaped curve of its exponential growth is converted to an S shaped curve of logistic growth (growth that fluctuates around the carrying capacity of its habitat) (Figure 7.16, right) The population sizes of some species often fluctuate above and below their carrying capacity.

Coevolution

At the individual level, members of predator species benefit from their predation and members of prey species are harmed. At the population level, predation plays a role in natural selection. Animal predators tend to kill the sick, weak, aged, and least fit members of a prey population because they are the easiest to catch. Individuals with better defence against predation thus tend to survive longer and leave more offsprings with adaptations that can help them avoid predation. Over time, as a prey species develops traits that make it more difficult to catch, its predators face selection pressure that favor traits increasing their ability to catch their prey. Then the prey species must get better at eluding the more effective predators. This back and forth adaptation cycle is called coevolution. Changes in the gene pool of one species leads to changes in the gene pool of another species.

What four variable governs changes in population size?

Births, deaths, immigration, and emigration. A population increases through bird and immigration (arrival of individuals from outside the population). Populations decrease through death and emigration (departure of individuals from the population). Population change= Individuals added- Individuals lost Population change= (Births+ Immigration) - (Deaths + Emigration)

intraspecific competition

Competition among members of the same species

Pioneer species

First species to populate an area during primary succession. They often have seeds or spores that can travel long distances and quickly spread, usually over the rocks that are exposed. Pioneer species such as lichens release acids that can break down the rock and start soil formation process. As the soil slowly forms, small plants, insects, and worms invade and add more nutrients that build up the soil. Each successive wave of new organisms changes the environmental conditions in ways that provide more nutrients, habitats, and favorable environmental conditions for future arrivals.

7.1 How do Species Interact? concept

Five types of interactions among species (interspecific competition, predation, parasitism, mutualism, and commensalism) affect the resource use and population sizes of species.

7.3 What Limits the Growth of Populations? Concept

No population can grow indefinitely because of limitations on resources and because of competition among species for those resources.

Scientists use sampling techniques to estimate the sizes of large populations of species such as oak trees that are spread over a large area and squirrels that move around and are hard to count. Typically, they count the number of individuals in one or more small sample areas and use this information to estimate the number of individuals in a larger area.

Populations of difference species vary in their distribution over their habitats (dispersion). Most populations live together in clumps or groups (pack of wolves, schools of fish, flocks of birds). Living in groups allows organisms to cluster where resources are available. Group living also provides some protection from predators, and gives some predator species a better chance of getting a meal.

Predator-prey relationship has a strong effect on population sizes and other factors in many ecosystems. Ex: Sea urchins prey on kelp. Southern sea otters are a keystone species because they prey on sea urchins, preventing them from destroying the kelp forests. Predators use variety of ways to help them capture pray. Herbivores can walk, swim, or fly to the plants they feed on. Many carnivores, such as cheetahs, use speed to chase down and kill prey, such as zebras. Eagles and hawks can fly and have keen eyesight to find prey. Some predators such as female African lions work in groups to capture large or fast-running prey. Other predators use camouflage to hide in plain sight and ambush their prey. Some predators use chemicals such as venom to paralyze their prey and deter predators.

Prey species have evolved many ways to avoid predators. Some can run, swim, or fly fast and some have highly developed sense of sight, sound, or smell that alert them to the presence of predators. Pray species also use camouflage to blend into their surroundings. Some use chemical warfare to discourage predators from eating them. Either by emitting chemicals that are poisonous, irritating, smell, or bad tasting. Many bad tasting, bad smelling, toxic, or stinging prey species flash a warning coloration that eating them is risky. Prey species also use mimicry (common in butterflies) where they act like other more dangerous species. Prey also use behavioral strategies. For example, the pufferfish blows up. Some gain protection by living in large groups (schools of fish, herds of antelope). Moths have wings that look like the eyes of larger animals. Biologists Edward O. Wilson proposed two criteria for evaluating the dangers posed by various brightly colored animal species. 1. If they are small and strikingly beautiful, they are probably poisonous. 2. If they are stinkingly beautiful and easy to catch, they are probably deadly.

J Curve

Some species have an incredible ability to increase their numbers and grow exponentially. Plotting these numbers against time yields a J shaped curve of exponential growth when a population increases by a fixed percentage each year. Members of such populations typically reproduce at an early age, have many offspring each time they reproduce, and reproduce many times with short intervals between generations. Ex: bacteria and many insect species. Exponential growth only occurs in nature when species with a high reproductive potential have few predators, plenty of food and other resources, and little competition from other species for such resources. However, there are always limits to population growth in nature. Research reveals that a rapidly growing population of any species eventually reaches some size limit imposed by limiting factors. These factors include sunlight, water, temperature, space, or nutrients, or exposure to predators or infectious diseases is the sum of all such factors in a habitat. Limiting factors largely determine an area's carrying capacity

K selected species

Species that tend to reproduce later in life and have a small number of offspring with fairly long life spans. Typically, the offspring of k selected mammal species develop inside their mothers (where they are safe) and are born relatively large/ After birth, they mature slowly and are cared for and protected by one or both parents. In some cases, they live in herds or groups until they reach reproductive age. Such a species' population tends to be near the carrying capacity (K) of its environment. Many of these species especially those with low reproductive rates are vulnerable to extinction. Examples: Elephants, whale, and humans.

Competition

The most common interaction among species. It occurs when members of one or more species interact to use the same limited resources such as food, water, light (plants), and space.

ecoogical succession

The normally gradual change in species composition in a given terrestrial area or aquatic system. An important ecosystem service that can enrich the biodiversity of communities and ecosystems by increasing species diversity and interactions among species. Such interactions enhance sustainability by promoting population control and increasing the complexity of food webs. Two types, depending on the conditions present at the beginning of the process: Primary ecological succession and secondary ecological succession

Some solutions to taking care of white tailed deer

There are no easy solutions to the deer population problem in suburbs. Changes in hunting regulations that allow for the killing of more female deer have cut down the overall deer population. However, this has had a limited effect on deer populations in suburban areas because it is too dangerous to allow widespread hunting with guns in such populated communities. Some areas have hired experienced and licensed archers who use bows and arrows to help reduce deer numbers. To protect nearby residents the archers hunt from elevated tree stands and only shoot their arrows downward. Some communities spray the scent of deer predators or of rotting deer meat in edge areas to scare off deer. Others scare off deer by using electronic equipment that emits high frequency sounds that humans cannot hear. Some homeowners surround their gardens and yards with high, black plastic mesh fencing. Deer can be trapped and moved from one area to another, but this is expensive and must be repeated whenever they move back into an area. In addition, there are questions concerning where to move the deer and how to pay for such programs. Darts loaded with contraceptives can be shot into female deer to hold down their birth rates, but this is expensive and must be repeated every year. One possibility is an experimental, single shot contraceptive vaccine that lasts for several years. Another approach is to trap dominant males and use chemical injections to sterilize them. Both of these approaches are costly and will require years of testing. Suburban dwellers could also stop planting trees, shrubs, and flowers that attract deer around their homes.

All living systems, from a cell to the biosphere, constantly change in response to changing environmental conditions. Living systems have complex processes that interact to provide some degree of stability or sustainability. This stability, or the capacity to withstand external stress and disturbance is maintained by constant change in response to changing environmental conditions. In a mature tropical rain forest, some trees die and other take their places. However, unless the forest is cut, burned, or otherwise destroyed you would still recognize it as a tropical rain forest 50 or 100 years from now.

Two aspects of stability or sustainability in ecosystems. 1. Inertia/persistence 2. resilience Evidence suggests that some ecosystems only have one of these properties but not the other. Tropical rain forests have high species diversity and high inertia and thus are resistant to low levels of change or damage. But once a large tract of tropical rain forest is cleared or severely damaged, the resilience of degraded forest ecosystem may be so low that the degradation reaches an ecological tipping point. Beyond that point, the forest might not be restored by secondary ecological succession. One reason is that most of the nutrients in a tropical rain forest are stored in its vegetation, not the topsoil. Once the nutrient rich vegetation is gone, frequent rains on a large cleared area of land can remove most of the remaining soil nutrients and thus prevent the return of a tropical rain forest to such an area. By contrast, grasslands are much less diverse than most forests. Thus, they have low inertia and can burn easily. Because most of their plant matter is stored in underground roots, these ecosystems have high resilience and can recover quickly after a fire because their root systems produce new grasses. Grassland can be destroyed only if its roots are plowed up and something else is planted in its place, or if it is severely overgrazed by livestock or other herbivores.

Resource partitioning

When difference species competing for similar scare resources evolve specialized traits that allow them to share the same resources. This can involve using parts of the resources or using the resources at different times or in different ways. Adaptations allow the birds to reduce competition by feeding in different portions of certain spruce trees and by feeding on different insect species.

Mutualism

When two species interact in ways that benefit both by providing each with food, shelter, or some other resource. Ex: Pollination process of flowers by bees, hummingbirds, and butterflies. Ex: Oxpeckers which ride on the heads of large animals, removing and eating parasites and pest from the animals' bodies and make noises when predators are approaching. Mutualism is not cooperating between two species, each one is only concerned for their survival.

secondary ecological succession

Where a series of terrestrial communities or ecosystems with different species develop in places containing soil or bottom sediment. This type of succession begins in an area where an ecosystem has been disturbed, removed, or destroyed, but some soil or bottom sediment remains. Ex: abandoned farmland, burned or cut forests, etc. Because some soil or sediment is present, new vegetation can begin to grow, usually within a few weeks. On land, growth begins with the germination of seeds already in the soil and seeds imported by wind or in the droppings of birds and other animals.

Interspecific competition

competition between different species. It plays a larger role in most ecosystems compared to intraspecific competition When two species compete with one another for the same resources, their niches overlap. The greater this overlap, the more they compete for key resources. For example, if species A take over the largest share of one or more key resources, then competing species B must move to another area (if possible) or suffer a population decline. Given enough time for natural selection to occur, populations can develop adaptations that enable them to reduce or avoid competition with other species. Ex: resource partitioning

Primary ecological succession

involves the gradual establishment of communities of different species in lifeless areas. This type of succession begins where there is o soil in a terrestrial ecosystem or no bottom sediment in an aquatic ecosystem. Usually takes hundreds to thousands of years because of the need to build up fertile soil or aquatic sediments to provide the nutrients needed to establish a plant community.

survivorship curve

shows the percentages of the members of a population surviving at different ages. This is because species with different reproductive strategies tend to have different life expectancies. Three generalized types of survivorship curves: late loss (Type 1), constant loss (Type II), and early loss (Type III) A late loss population (k selected species) typically has high survivorship to a certain age, and them high morality. A constant loss population (most songbirds) typically has a constant death rate at all ages. Early loss population (many r selected species and annual plants) have low survivorship in early life. These generalized survivorship curves only approximate the realities of nature.

R selected species

species with a capacity for a high rate of population growth. These species tend to have short life spans and produce many, usually small offspring and give them little or no parental care. As a result, many of the offspring die at an early age. To overcome such losses, r selected species produce large numbers of offspring so that a few will likely survive and have many offspring to sustain the species. Ex: algae, bacteria, frogs, most insects, and many fish. These specie tend to be opportunists. They reproduce and disperse rapidly when conditions are favorable or when a disturbance such as a fire or clear cutting of a forest opens up a new habitat or niches for invasion. Once established, their populations may crash because of unfavorable changes in environmental conditions or invasion by more competitive species. This explains why many opportunist species go through irregular and unstable boom and burst cycles in their population sizes.

Carrying capacity

the maximum population of a given species that a particular habitat can sustain indefinitely. Carrying capacity for a population is not fixed and can rise or fall as environmental conditions change the factors that limit the population's growth.

prey

the species that gets eaten by another species

Density dependent factors

variables that become more important as a population's density increases. Ex: in a dense population parasites and diseases can spread more easily, resulting in higher death rates. On the other hand, a high population density helps sexually reproducing individuals to find mates more easily to produce offspring. Factors such as flood, fires, landslides, drought, and climate change are considered density independent factors because the effect they have on a population's size is not related to the population's density.

Limiting factors

various physical or chemical factors that can determine the number of organisms in a population and how fast a population grows or declines. Limiting factors are sometimes more important than other factors in regulating population growth. On land, precipitation often is the limiting factor. Low precipitation levels in desert ecosystems limit desert plant growth. Lack of key soil nutrients limits the growth of plants, which in turn limits populations of animals that eat plants, and animals that feed on plant eating animals. Limiting physical factors for populations in aquatic systems include water temperature, water depth, and water clarity (allowing for more or less sunlight). Other important factors are nutrient availability, acidity, salinity, and the level of oxygen gas in the water (dissolved oxygen content).

Parasitism

when one species (the parasite) lives in or on another organism (the host). The parasite benefits by extracting nutrients from the host. A parasite weakens its host but rarely kills it, since doing so would eliminate the source of its benefits. Some parasites (such as fleas and ticks) move from one host to another Parasites help keep their host populations in check.