Unit 8 - Ecology

8.1: Behavioral Ecology

• Behavioral ecology and ethology both involve the study of animal behavior.
• Behavioral ecology - focuses on the interaction between animals and their environments, and usually includes an evolutionary perspective.
• Ethology a narrower field, focused particularly on animal behavior and less on ecological analysis.

8.2: Types of Animal Learning

• Associative learning the process by which animals take one stimulus and associate it with another.
• Ivan Pavlov demonstrated classical conditioning, a type of associative learning, with dogs.
  • Pavlov taught dogs to anticipate the arrival of food with the sound of a bell.
  • He hooked up these dogs to machines that measured salivation.
  • He began the experiments by ringing a bell just moments before giving food to the dogs.
  • Soon after this experiment began, the dogs were salivating at the sound of the bell before food was even brought into the room.
  • They were conditioned to associate the noise of the bell with the impending arrival of food; one stimulus was substituted for another to evoke the same response.
• Fixed-action pattern (FAP) - an innate, preprogrammed response to a stimulus.
  • Once this action has begun, it will not stop until it has run its course.
  • For example, male stickleback fish are programmed to attack any red-bellied fish that come into their territory.
  • Males do not attack fish lacking this red coloration; it is specifically the color that stimulates aggressiveness.
• Habituation the loss of responsiveness to unimportant stimuli.
  • Example - little ducklings run for cover whenever birdlike objects fly overhead.
  • If one were to throw bird-shaped objects over their heads, in the beginning they would head for cover each time one flew past them, but over time as they learned that the fake birds did not represent any real danger, they would habituate to it and eventually not react at all.
• Imprinting an innate behavior that is learned during a critical period early in life.
  • For example, when geese are born, they imprint on motion that moves away from them, and they follow it around accepting it as their mother.
  • This motion can be the baby’s actual mother goose, it can be a human, or it can be an object.
  • Once this imprint is made, it is irreversible.
• Insight learning the ability to do something right the first time with no prior experience.
  • It requires reasoning ability—the skill to look at a problem and come up with an appropriate solution.
• Observational learning the ability of an organism to learn how to do something by watching another individual do it first, even if they have never attempted it themselves.
  • An example of this involves young chimpanzees in the Ivory Coast, who watch their mothers crack nuts with rock tools before learning the technique themselves.
• Operant conditioning a type of associative learning that is based on trial and error.
  • This is different from classical conditioning because in operant conditioning, the association is made between the animal’s own behavior and a response.
  • This is the type of conditioning that is important to the aposematically colored organisms.
  • For example, a brightly colored lizard with a chemical defense mechanism (it can spray predators in an attempt to escape) relies on this type of conditioning for survival.
  • The coloration pattern is there in the hope that the predator will, in a trial-and-error fashion, associate the coloration pattern with an uncomfortable chemical-spraying experience that it had in the past.
  • This association might make the predator think twice before attacking in the future and provide the prey with enough time to escape.

8.3: Animal Movement

• Kinesis - a seemingly random change in the speed of a movement in response to a stimulus.

  • When an organism is in a place that it enjoys, it slows down, and when in a bad environment, it speeds up.
  • Overall this leads to an organism spending more time in favorable environments.

• Migration - a cyclic movement of animals over long distances according to the time of year.

  • Birds are known to migrate south, where it is warmer, for the winter.

• Taxis **a reflex movement toward or away from a stimulus.

  • Moths fly into bug lights because of the taxis response.
  • They are drawn to the light at night (phototaxis).

  Behavior patterns

• Agonistic behavior - Behavior that results from conflicts over resources.

  • It often involves intimidation and submission.
  • The battle is often a matter of who can put on the most threatening display to scare the other one into giving up, although the displays can also be quite subtle.
  • Agonistic behaviors can involve food, mates, and territory, to name only a few.
  • Participants in these displays do not tend to come away injured because most of these interactions are just that: displays.

• Altruistic behavior - An altruistic action is one in which an organism does something to help another, even if it comes at its own expense.

  • An example of this behavior involves bees.
  • Worker bees are sterile, produce no offspring, and play the role of hive defenders, sacrificing their lives by stinging intruders that pose a threat to the queen bee.

• Coefficient of relatedness - This statistic represents the average proportion of genes that two individuals have in common.

  • Siblings have a coefficient of relatedness (COR) of 0.5 because they share 50 percent of their genes.
  • This coefficient is an interesting statistic because it can be expected that an animal that has a high COR with another animal will be more likely to act in an altruistic manner toward that animal.

• Dominance hierarchies - A dominance hierarchy among a group of individuals is a ranking of power among the members.

  • The member with the most power is the “alpha” member.
  • The second-in-command, the “beta” member, dominates everyone in the group except for the alpha.
  • The dominance hierarchy is not necessarily permanent—there can always be some shuffling around.
  • For example, in chimpanzees, an alpha male can lose his alpha status and become subordinate to another chimp if power relationships change.
  • One positive thing about these hierarchies is that since there is an order, known by all involved, it reduces the energy wasted and the risk from physical fighting for resources.

• Foraging - the feeding behavior of an individual.

  • This behavior is not as random as it may seem as animals tend to have something called a search image that directs them toward their potential meal.
  • When searching for food, few fish look for a particular food; rather, they are looking for objects of a particular size that seem to match the size of what they usually eat.
  • This is a search image.

• Inclusive fitness - represents the overall ability of individuals to pass their genes on to the next generation.

  • This includes their ability to pass their own genes through reproduction as well as the ability of their relatives to do the same.
  • Reproduction by relatives is included because related individuals share many of the same genes.
  • Therefore, helping relatives to increase the success of passage of their genes to the next generation increases the inclusive fitness of the helper.

• Optimal foraging - Natural selection favors animals that choose foraging strategies that take into account costs and benefits.

  • For example, food that is rich in nutrients but far away may cost too much energy to be worth the extra trip.
  • There are many potential costs to traveling a long distance for some food—the animal itself could be eaten on the way to the food, and the animal could expend more energy than it would gain from the food.

• Reciprocal altruism - reason individuals behave altruistically: the hope that in the future, the companion will return the favor.

  • A baboon may defend an unrelated companion in a fight, or perhaps a wolf will offer food to another wolf that shares no relation.
  • Animals rarely display this behavior since it is limited to species with stable social groups that allow for exchanges of this nature.

• Territoriality - Territorial individuals defend a physical geographic area against other individuals.

  • This area is defended because of the benefits derived from it, which may include available mates, food resources, and high-quality breeding sites.
  • An individual may defend a territory using scent marking, vocalizations that warn other individuals to stay away, or actual physical force against intruders.
  • Animal species vary in their degree of territoriality (in fact, some species are not territorial), and both males and females may exhibit territorial behavior.

8.4: Animal Communication

• Chemical communication - Mammals and insects use chemical signals called pheromones, which in many species play a pivotal role in the mating game.
• Pheromones can be powerful enough to attract mates from miles away.
• Visual communication - example of a visual display is a male peacock’s feather splay, which announces his willingness to mate.
• Auditory communication - This mode of communication involves the use of sound in the conveying of a message.
• Tactile communication - This mode of communication involves touch in the conveying of a message and is often used as a greeting.
• Bees provide an example of communication that involves chemical, tactile, and auditory components.

8.5: Ecology

• Ecology the study of the interaction of organisms and their environments.

8.6: Population Ecology and Growth

• Population - a collection of individuals of the same species living in the same geographic area.

• Community - collection of populations of species in a geographic area**.**

• Ecosystem - consists of the individuals of the community and the environment in which it exists.

  • Ecosystems can be subdivided into abiotic and biotic components.

• Biotic components - the living organisms of the ecosystem

• Abiotic components - the nonliving players in an ecosystem, such as weather and nutrients.

• Biosphere is the entire life-containing area of a planet—all communities and ecosystems.

• Niche of an organism - consists of all the biotic and abiotic resources used by the organism.

• population density - describes how many individuals are in a certain area.

• Distribution - describes how populations are dispersed over that area.

• Distribution patterns:

  • Clumped: The individuals live in packs that are spaced out from each other, as in schools of fish or herds of cattle.
  • Uniform: The individuals are evenly spaced out across a geographic area, such as birds on a wire sitting above the highway.
  • Random: The species are randomly distributed across a geographic area, such as a tree distribution in a forest.

• Population ecology the study of the size, distribution, and density of populations and how these populations change with time.

• It takes into account all the variables we have mentioned already and many more.

• The size of the population, symbolized N, indicates how many individuals of that species are in a given area.

• Demographers study the theory and statistics behind population growth and decline.

• Demographic statistics:

  • Birth rate - offspring produced per time period. Highest among those in the middle of the age spectrum.
  • Death rate - number of deaths per time period. Highest among those at two extremes of the age spectrum.
  • Sex ratio - proportion of males and females in a population.
  • Generation time - time needed for individuals to reach reproductive maturity.
  • Age structure - statistic that compares the relative number of individuals in the population from each age group.
  • Immigration rate - rate at which individuals relocate into a given population.
  • Emigration rate - rate at which individuals relocate out of a given population.

• All these statistics together determine the size and growth rate of a given population.

• A higher birth rate and a lower death rate will give a faster rate of population growth.

• A high female sex ratio could lead to an increase in the number of births in a population (more females to produce offspring).

• A short generation time allows offspring to be produced at a faster rate.

• An age structure that consists of more individuals in the middle of their reproductive years will grow at a faster rate than one weighted toward older people.

  Population growth and size

• Biotic potential the maximum growth rate of a population given unlimited resources, unlimited space, and lack of competition or predators.

• This rate varies from species to species.

• Carrying capacity defined as the maximum number of individuals that a population can sustain in a given environment.

• Limiting factors help control population sizes.

• A few examples of limiting factors - predators, diseases, food supplies, and waste produced by organisms.

• Density-dependent factors - Come into play as the population approaches and/or passes the carrying capacity.

  • Examples of density-dependent limiting factors - food supplies, which run low; waste products, which build up; and population-crowding-related diseases such as the bubonic plague.

• Density-independent factors - These limiting factors have nothing to do with the population size.

  • Examples of density-independent limiting factors - floods, droughts, earthquakes, and other natural disasters and weather conditions.

• Types of population growth

  • Exponential growth: the population grows at a rate that creates a J-shaped curve. The population grows as if there are no limitations as to how large it can get (biotic potential).
  • Logistic growth: the population grows at a rate that creates an S-shaped curve. Limiting factors are the culprits responsible for the S shape of the curve, putting a cap to the size to which the population can grow.

8.7: Life History Strategies

• K-selected populations: populations of a roughly constant size whose members have low reproductive rates.
  • The offspring produced by these *K-*selected organisms require extensive postnatal care until they have sufficiently matured.
  • Humans are a fine example of a *K-*selected population.
• R-selected populations: populations that experience rapid growth of the J- curve variety. The offspring produced by *R-*selected organisms are numerous, mature quite rapidly, and require very little postnatal care.
  • These populations are also known as opportunistic populations and tend to show up when space in the region opens up as a result of some environmental change.
  • The opportunistic population grows fast, reproduces quickly, and dies quickly as well.
  • Bacteria are a good example of an Rselected population.
• Survivorship curves - another tool used to study the population dynamics of species.
• These curves show the relative survival rates for population members of different ages.

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• Type I individuals live a long life until an age is reached where the death rate in the population increases rapidly, causing the steep downward end to the type I curve.
  • Examples of type I organisms include humans and other large mammals.
• Type II individuals have a death rate that is reasonably constant across the age spectrum.
  • Examples of type II species include lizards, hydra, and other small mammals.
• Type III individuals have a steep downward curve for those of young age, representing a death rate that flattens out once a certain age is reached.
  • Examples of type III organisms include many fishes, oysters, and other marine organisms.

8.8: Biological Communities

• Most species exist within a community.

• Because they share a geographic home, they are bound to interact with one another.

• These interactions range from positive to neutral to negative.

• The communities are characterized by the amount of energy they are able to-produce (primary productivity) and the number of species present in the community.

  Ecological Niche

• Niche of an organism - represents all the biotic and abiotic resources used by organisms in a given area.

• However, species sometimes are not able to occupy their entire niche due to the presence or absence of other species.

• These interactions with other species **may have harmful (negative) or helpful (positive) effects on the species.

• Fundamental niches - all the resources and area that a species can occupy.

• Realized niches - the actual resources and space that an organism occupies.

• Competition between species for resources in a niche leads to the competitive exclusion principle: when two species compete for limited resources and one of the species uses the resources more efficiently than the other, it will lead to the elimination of the less efficient species.

  Forms of Species Interaction

• Symbiosis - A symbiotic relationship is one between two different species that can be classified as one of three main types: commensalism, mutualism, or parasitism.

• Commensalism - One organism benefits while the other is unaffected. Cattle egrets feast on insects that are aroused into flight by cattle grazing in the insects’ habitat. The birds benefit because they get food, but the cattle do not appear to benefit at all.

• Mutualism - Both organisms reap benefits from the interaction. One popular example of a mutualistic relationship is that between acacia trees and ants. The ants are able to feast on the sugar produced by the trees, while the trees are protected by the ants’ attack on any potentially harmful foreign insects.

• Parasitism*.* One organism benefits at the other’s expense. A popular example of a parasitic relationship involves tapeworms, which live in the digestive tract of their hosts. They reap the benefits of the meals that their host consumes by stealing the nutrients and depriving the host of nutrition.

• Competition. Both species are harmed by this kind of interaction. The two major forms of competition are intraspecific and interspecific competition.

  • Intraspecific competition within species competition. This kind of competition occurs because members of the same species rely on the same valuable resources for survival. When resources become scarce, the most fit of the species will get more of the resource and survive.
  • Interspecific competition is competition between different species.

• Predation - One species, the predator, hunts another species, the prey.

  • Not all prey give in to this without a fight, and the hunted may develop mechanisms to defend against predatory attack.

  Defense Mechanisms

• Aposematic coloration It is warning coloration adopted by animals that possess a chemical defense mechanism.

  • Predators have grown cautious of animals with bright color patterns due to past encounters in which prey of a certain coloration have sprayed the predator with a chemical defense.

• Batesian mimicry - an animal that is harmless copies the appearance of an animal that is dangerous to trick predators.

• Cryptic coloration - those being hunted adopt a coloring scheme that allows them to blend into the colors of the environment

• Deceptive markings can cause a predator to think twice before attacking. For example, some insects may have colored designs on their wings that resemble large eyes, causing individuals to look more imposing than they truly are.

• Müllerian mimicry - two species that are aposematically colored as an indicator of their chemical defense mechanisms mimic each other’s color scheme in an effort to increase the speed with which their predators learn to avoid them. The more often predators see dangerous prey with this coloration, the faster the negative association is made.

• When the prey population starts to decrease because of predation, there is a reactionary reduction in the predator population.

• The predators run low on a valuable resource necessary to their survival—their prey.

• As the predator population declines, an increase in the population of the prey begins to appear because more of those prey animals are able to survive and reproduce.

• As the prey population density rises, the predators again have enough food available to sustain a higher population, and their population density returns to a higher level again.

• Unless disturbed by a dramatic environmental change, this cyclical pattern continues.

• Coevolution mutual evolution between two species and is often seen in predator–prey relationships.

• In order to survive, the predator must evolve so that it can catch its victim and eat.

  Succession

• The shift in the local composition of species in response to changes that occur over time.

• As time passes, the community goes through various stages until it arrives at a final stable stage called the climax community.

• Primary succession occurs in an area that is devoid of life and contains no soil.

• A pioneer species (usually a small plant) able to survive in resource-poor conditions takes hold of a barren area such as a new volcanic island.

• The pioneer species does the grunt work, adding nutrients and other improvements to the once uninhabited volcanic rock until future species take over.

• As the plant species come and go, adding nutrients to the environment, animal species are drawn in by the presence of new plant life.

• These animals contribute to the development of the area with the addition of further organic matter (waste).

• This constant changing of the guard continues until the climax community is reached and a steady-state equilibrium is achieved.

• Bare-rock succession involves the attachment of lichen to rocks, followed by the step- by-step arrival of replacement species up to the climax community.

• Pond succession is kicked off when a shallow, water-filled hole is created.

• As time passes, animals arrive on the scene as the pioneer species deposit debris, encouraging the growth of vegetation on the pond floor.

• Over time, plants develop whose roots are underwater and whose leaves are above the water.

• As these plants begin to cover the entire area of the pond, the debris continues to build up, transforming the once empty pond into a marsh.

• When enough trees fill the area, the marsh becomes a swamp.

• If the conditions are appropriate, the swamp can eventually become a forest or grassland, completing the succession process.

• Secondary succession occurs in an area that once had stable life but has since been disturbed by some major force such as a forest fire.

• This type of succession is different from primary succession because there is already soil present on the terrain when the process begins.

8.9: Trophic Levels

Autotrophs

• Photoautotrophs (photosynthetic autotrophs) start the Earth’s food chain by converting the energy of light into the energy of life.
• Chemoautotrophs (chemosynthetic autotrophs) release energy through the movement of electrons in oxidation reactions.
• Heterotrophs: The consumers of the world.
• They are able to obtain their energy only through consumption of other living things.
• Herbivore feeds on plants for nourishment.
• Carnivore - obtains energy and nutrients through the consumption of other animals.
• Detritivore - obtains its energy through the consumption of dead animals and plants.
• Subcategory of this type of consumer -decomposers - consume dead animal and plant matter, but then release nutrients back into the environment.

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• The distribution of energy on the planet can be subdivided into a hierarchy of energy levels called trophic levels.
• The primary producers make up the first trophic level.
• The next trophic level consists of the organisms that consume the primary producers: the herbivores.
• These organisms are known as primary consumers.
• The primary consumers are consumed by the secondary consumers, or primary
• carnivores, that are the next trophic level.
• These primary carnivores are consumed by the secondary carnivores to create the next trophic level.
• Biomass pyramid - represents the cumulative weight of all of the members at a given trophic level.
• pyramid of numbers - based on the number of individuals at each level of the biomass chain.
• Food chain - a hierarchical list of who consumes who.
• For example, bugs are eaten by spiders, who are eaten by birds, who are eaten by cats.
• Food web provides more information than a food chain.
• Food webs can be regarded as overlapping food chains that show all the various dietary relationships.

8.10: Biomes

• Biomes - The various geographic regions of the Earth that serve as hosts for ecosystems.
• Deserts - The driest land biome of the group, deserts experience a wide range of temperature from day to night and exist on nearly every continent.
• Deserts that do not receive adequate rainfall will not have any vegetative life.
• However, plants such as cacti flourish in this biome, given enough water.
• Much of the wildlife found in deserts is nocturnal and conserves energy and water during the heat of the day.
• This biome shows the greatest daily fluctuation in temperature due to the fact that water moderates temperature.
• Savanna - contain a spattering of trees, are found throughout South America, Australia, and Africa.
• Savanna soil tends to be low in nutrients, while temperatures tend to run high.
• Many of the grazing species of this planet (herbivores) live here.
• Taiga - characterized by lengthy cold and wet winters, found in Canada and has gymnosperms as its prominent plant life.
• Taigas contain coniferous forests (pine and other needle-bearing trees).
• Temperate deciduous forests - found in regions that experience cold winters where plant life is dormant, alternating with warm summers that provide enough moisture to keep large trees alive.
• Can be seen in the northeastern United States, much of Europe and eastern Asia.
• Temperate grasslands - found in regions with cold winters.
• The soil is considered to be among the most fertile of all here.
• Receives less water than tropical savannas.
• Tropical forests - found all over the planet in South America, Africa, Australia, and Asia, tropical forests come in many shapes and sizes.
• Near the equator, they can be rainforests, whereas in lowland areas that have dry seasons, they tend to be dry forests.
• Rainforests consist primarily of tall trees that form a thick cover, which blocks the light from reaching the floor of the forest (where there is little growth).
• Known for their rapid recycling of nutrients and contain the greatest diversity of species.
• Tundras - experience extremely cold winters during which the ground freezes completely.
• The upper layer of the ground is able to thaw during the summer months, but the land directly underneath, called the permafrost, remains frozen throughout the year.
• This keeps plants from forming deep roots in this soil and dictates what type of plant life can survive.
• The plant life that tends to predominate is short shrubs or grasses that are able to withstand difficult conditions.
• Water biomes - Both freshwater and marine water biomes occupy the majority of the surface of the Earth.

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8.11: Biogeochemical Cycles

• Biogeochemical cycles - represent the movement of elements, such as nitrogen and carbon, from organisms to the environment and back in a continuous cycle.
• Carbon cycle -Carbon is the building block of organic life.
• The carbon cycle begins when carbon is released to the atmosphere from volcanoes, aerobic respiration (CO2), and the burning of fossil fuels (coal).
• Most of the carbon in the atmosphere is present in the form of CO2.
• Plants contribute to the carbon cycle by taking in carbon and using it to perform photosynthetic reactions, and then incorporating it into their sugars.
• The carbon is ingested by animals, who send the carbon back to the atmosphere when they die.
• Nitrogen cycle - Nitrogen is an element vital to plant growth.
• Plants have nitrogen to consume due to the existence of organisms that perform the thankless task of nitrogen fixation— the conversion of N2 to NH3 (ammonia).
• The only source of nitrogen for animals is the plants they consume.
• When these organisms die, their remains become a source of nitrogen for the remaining members of the environment.
• Bacteria and fungi (decomposers) eat at these organisms and break down any nitrogen remains.
• The NH3 in the environment is converted by bacteria into NO3(nitrate), and this NO3 is taken up by plants and then eventually by animals to complete the nitrogen cycle.
• Denitrification - the process by which bacteria themselves use nitrates and release N2 as a product.

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• Water cycle - A considerable amount of water evaporates each day and returns to the clouds.
• Eventually, this water is returned to the earth in the form of precipitation.

8.12: Disruptions to Ecosystem

• An invasive species is an organism that is introduced to an area that is not native to the particular area and that leads to environmental harm to the area.
• While not all non-native species are invasive, invasive species are often able to outcompete native species for abiotic and biotic resources, leading to uncontrolled population growth and changes in the ecosystem.
• Invasive species can be introduced in many different ways, including accidentally or intentionally.
• Either way, they negatively impact the native ecosystem.
• Local and global ecosystems naturally change over time.
• Humans accelerate the change in many ways.
  • Include: introduction of invasive species, overpopulation, deforestation, pollution, and burning fossil fuels.
• These negative human impacts have caused climate change, soil erosion, and reduced air and water quality, leading to local and global ecosystem changes

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