Ch 55 Community Ecology

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A biological community consists of

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Interacting species, usually living within a defined area

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Commensalism

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Occurs when one species benefits but the other species is unaffected + / 0

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Competition

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Occurs when individuals use the same resources resulting in lower Fitness for both. - / -

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Consumption

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Occurs when one organism eats or absorbs nutrients from another, increasing the consumers Fitness but decreasing the victims Fitness + / -

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Mutualism

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Occurs when two species interact in a way that confers Fitness benefits to both + / +

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as you analyze each type of species interaction watch for three key themes

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1. Species interactions may affect the distribution and abundance of a particular species.

2. Species Act as agents of natural selection when they interact. And biology, co-evolutionary arms race occurs between predators and prey, between parasites and hosts, and between other types of interacting species.

3. The outcome of interactions among species is dynamic and conditional

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Commensalism example

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And stir up insects while hunting, and birds tag along and benefit by eating insects that are stirred up by the ants

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Intraspecific competition

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Occurs between members of the same species. Because intraspecific competition for resources intensifies as a population density increases, it is a major cause of density dependent growth

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Interspecific competition

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Occurs when members of different species use the same limiting resources. Competition between niches of two interacting species

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Gauss's experiments illuminated an important distinction

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1. The species fundamental Niche is the resource it uses or conditions it tolerates in the absence of competitors.

2. A species realized Niche is the resource that uses or condition tolerates when competition occur

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If a symmetric competition occurs and the niches of the two species do not overlap completely

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The week or competitor will move from its fundamental Niche to a realized Niche, ceding some resources to the stronger competitor

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Asymmetric competition

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One species has a distinct advantage over another species

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Symmetric competition

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All species are equally capable of utilizing a resource however when they are in the same spot none of them will out-compete each other but their overall Fitness of all species will decrease but not go extinct

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Question why is the distribution of adult chthamalus restricted to the upper intertidal zone. Hypothesis, adult C are out competed in the lower intertidal zone

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Experiment setup. 1. Transplant rocks containing young to Thalamus to lower intertidal zone. Too. Let semi balanus colonize the rocks. 3. Remove seven violinist from half of each Rock monitor survival of Thelma's on both sides. Projection, mm survive better and the absence of sumida baldness. Conclusion to Chamas do not occur in the lower intertidal zone because they are out competed by $7

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If individuals are extremely good at competing for a particular resource, they are probably less good at in during drought conditions, warding off disease, or preventing predation

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Because there is a fitness trade-off

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One of the major threats to communities is invasive species

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Recent experiments have shown that can use that contain a large number of different species have more resistance to Invasion than communities with a smaller number species, in other words, competition can help communities resist invasion

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Herbivory

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Is the consumption a plant tissues by herbivores

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Parasitism

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The consumption of small amounts of tissues from another organism, or host, by a parasite. Example lamprey

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Predation

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Is the killing and consumption of most or all of another individual, the prey, by The Predator

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Natural selection strongly favors traits that allow

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Individuals to avoid being eaten

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Constitutive or standing defenses are defenses that are always present and include

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Avoidance, hiding with or without camouflage, or running, flying or swimming away. Poison, many plants least their tissues with compounds that are toxic to Consumers. Schooling and flocking behaviors that confuse predators. Fighting back, with the use of Weaponry or toxins

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Cryptic coloration

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Cryptic coloration help spray such as this Leaf grasshopper escaped detection

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Batesian mimics

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Look dangerous but are not dangerous

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Müllerian mimics

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look dangerous, and are dangerous

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Question are muscles defenses induced by the presence of crabs. Hypothesis muscles increase investment in defense in the presence of crabs

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Predictions, muscles Downstream of the crab tank will have thicker shells than muscles Downstream of the empty tank. Conclusion muscles increase investment defense when they detect crab's shell thickness is in inductable defense

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Experiments have supported the hypothesis that Predators play an important role in the density dependent growth of prey populations

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The data available to date indicate that in many instances, predators are efficient enough to reduce prey populations below carrying capacity

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Biologist routinely considered to hypothesis to help answer the question of why herbivores do not eat more of the food available

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1. The top-down control hypothesis, suggest that predation or disease limits herbivores.

2. The bottom-up limitation hypothesis suggests that plants provide poor nutrition or are well defended against herbivory

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Adaptation and arms race human immune defense against plasmodium

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1. Healthy liver cell has an HLA b53 protein on its membrane.

2. HLA b53 protein displays cp26 protein from plasmodium, indicating that the liver cell is infected.

3. Cytotoxic T-cell recognizes HLA b53 and cp26 complex.

4. Cytotoxic T-cell kills liver cell before more plasmodium cells are produced.

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Some plasmodium strains are particularly effective at infecting humans

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CP 26 and CP 29 have a low infection rate because hla-b 53 binds to these proteins and the immune response is effective. But cp27 and CP 28 have a high and average infection rate because hla-b 53 does not buy into these proteins and immune response is not as effective

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Can parasites manipulate their host

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Yes, and infected ant's abdomen turns red and the infected ant resembles a Perry and they will even climb up and stand on the higher branches with their butt in the air so they further look like a berry and get eaten by a bird so that the parasite can complete its life cycle

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And Agriculture and Forestry, the use of predators and parasites as bio control agents is a key part of integrated Pest Management

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Strategies to maximize crop in Forest productivity while using a minimum of insecticides or other types of potentially harmful compounds

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Examples of mutualism + / + interactions

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Mutualism between ants and the acacia trees. The trees provide a home for the ants and the Ants protect the trees. Mutualism between cleaner shrimp and a fish the cleaner shrimp eats debris in the fish's mouth getting a meal and the fish's mouth is clean and protected from infections

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Even though mutualism benefits both species, the interaction does not involve individuals from different species being altruistic

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The benefits received in a mutualism are a byproduct of each individual pursuing its own self-interest by maximizing its ability to survive and reproduce

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Mutualism I are dynamic. Such as the relationship between ants and treehoppers

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Ants get food from treehoppers because their waist is basically just sugar and ants in return protect treehoppers from jumping spiders but when jumping spiders are not present treehoppers don't get any benefits from the ants

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If communities are predictable assemblages, the same group of species should almost always be found growing together

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Historical data on plant communities show that groups of species change their range independently of one another. Fossil pollen studies suggest that plant Community composition has always been Dynamic, rather than static

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Although both biotic interactions and climate are important in determining which species exists at a certain site

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Chance and history also play a large role

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How do keystone species structure communities. Even though species are not predictable assemblages, the structure of a community can change dramatically if a single species of predator or herbivore is removed from or added to a community

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A keystone species is a species that has a much greater impact on the surrounding species than its abundance would suggest

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For example the keystone species, the sea starpisaster a keystone species and some intertidal areas

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When pisaster was removed from experimental areas, the number of species present and the complexity of the habitat changed radically

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Disturbance is any event that remove some individuals or biomass from the community

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The important feature of a disturbance is that it alter some aspect of resource availability

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The impact of disturbance is the function of three factors

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1. type of disturbance .

2. Frequency of disturbance.

3. Severity of disturbance

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Most communities experienced a characteristic type of disturbance

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In most cases, disturbances occur with a predictable frequency and severity.

This is called a communities disturbance regime

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Ecologists use two approaches to determine the pattern of disturbance in a community

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1. Inference of long-term patterns from data obtained and short-term analysis.

2. reconstruction of the history of a particular site

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An example of a study to understand the disturbance of regine's

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They use fire scars in the growth rings of redwood trees and reconstruct history from the fire scars

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Succession

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Is the recovery, the development of communities, that follows a severe disturbance

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Primary succession

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Occurs when a disturbance removes the soil and it's organisms, as well as organisms that live above the surface

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Secondary succession

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Occurs when a disturbance remove some or all of the organisms from an area that leaves the soil intact

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Process secondary succession

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1. Pioneering species. Weedy species become established in the Disturbed soil.

2. Early successional community. Weedy species are replaced by longer-lived herbaceous species.

3. Mid successional community. Shrubs and short-lived trees begin to invade.

4. Climax community. Long Live trees species mature

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Three factors determine the pattern and rate of species replacement during succession at a particular time and place

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1. The particular traits of the species involved.

2. How the species interact.

3. Historical and environmental circumstances, such as the size of the area involved and weather conditions

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Dispersal capability and the ability to withstand harsh conditions are particularly important early in succession

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Pioneering species, the first organisms to arrive at a newly disturb site, tend to be weedy. Weeds are plants adapted for growth and Disturbed soils

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Early successional species devote most of their energy to reproduction and little too competitive ability

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These species have good dispersal ability can tolerate severe abiotic conditions and have high reproductive rates

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During succession, existing species can have one of three effects on subsequent species

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1. Facilitation occurs when earlier arriving species make conditions more favorable for the Rival of certain leader species.

2. Tolerance happens when existing species do not affect the probability that subsequent species will become established.

3. Inhibition occurs when the presence of one species inhibits the establishment of another

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Succession is also affected by the particular weather or climate conditions that occur during the process

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Variation in weather and climate causes different successional Pathways to occur in the same place at different times

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We see this in areas of Alaska where Glaciers are receding

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Cement exposed 20 years or less contain Willows. Sediments exposed a hundred years contain Sitka Alder and scattered Sitka spruce. Sediments exposed 150 to 200 years contain Den sick of spruce and Western hemlock

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Species richness

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Is the number of species present in a given community

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Species diversity

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Is a way to measure that incorporates a species relative abundance as well as its presence or absence

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The latitudinal gradient. To explain this pattern, biologists have had to consider two principles

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1. The Casual mechanism must be abiotic.

2. The species diversity of a particular area is the sum of four processes:

Speciation, Extinction, immigration, emigration

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Hypothesis to explain the latitudinal gradient. 1. High productivity hypothesis

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High productivity promotes High diversity

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Hypothesis to explain the latitudinal gradient. 2. Energy hypothesis

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High temperature increases productivity and the likelihood that organisms can tolerate the physical conditions in a region

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Hypothesis to explain the latitudinal gradient. 3. Area and age hypothesis

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Tropical regions have had more time and space for speciation than other regions

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Hypothesis to explain the latitudinal gradient. 4. Intermediate disturbance hypothesis

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Regions with a moderate type, frequency, and severity of disturbance should have high species richness and diversity