Ecology and the Biosphere
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Ch. 50 (Introduction to Ecology and the Biosphere)
I. Ecology is the scientific study of the interactions between organisms and the environment.
- Events that occur in the framework of ecological time translate into effects over the longer scale of evolutionary time.
- The environment of any organism includes two components.
- Abiotic, or nonliving, components - chemical and physical factors such as temperature, light, water, and nutrients.
- Biotic, or living, components - all the organisms, or the biota, that are part of the individual's environment.
- Ecology can be divided into areas of study ranging from the ecology of individual organisms to the dynamics of ecosystems and landscapes.
- Organismal ecology:
- Can be subdivided into the disciplines of physiological ecology, evolutionary ecology, and behavioral ecology.
- Concerns how an organism's structure, physiology, and behavior meet the challenges posed by the environment
- Population ecology:
- Concentrates mainly on factors that affect how many individuals of a particular species live in an area.
- Population - group of individuals of the same species living in a particular geographic area.
- Community ecology:
- Deals with the whole array of interacting species in a community.
- Community - all the organisms of all the species that inhabit a particular area
- Ecosystem ecology:
- The emphasis in this ecology is on energy flow and chemical cycling among the various biotic and abiotic components.
- Ecosystem - all the abiotic factors in addition to the entire community of species that exist in a certain area.
- Landscape ecology:
- Deals with arrays of ecosystems and how they are arranged in a geographic region.
- Patchiness is an environmental characteristic where a landscape or seascape consists of a mosaic of different types of patches.
- Focuses on the factors controlling exchanges of energy, materials, and organisms among the ecosystem patches.
- The biosphere is the global ecosystem, the sum of all the planet's ecosystems.
II. Interactions between organisms and the environment limit the distribution of species
- Biogeography is the study of the past and present distribution of individual species, in the context of evolutionary theory
- It provides a good starting point for understanding what limits the geographic distribution of a species.
- Factors limiting a species' distribution may include:
- Biotic factors.
- Abiotic factors.
- Dispersal is the movement of individuals away from centers of high population density or from their area of origin
- One way to determine if dispersal is a key factor limiting distribution is to observe the results of transplants of a species
- For a transplant to be considered successful, organisms must survive and reproduce in the new area
- If it is successful, the potential range of the species is larger than its actual range.
- Behavior and habitat selection may limit distribution.
- Plants may select their habitats by producing seeds that germinate only under a restricted set of environmental conditions
- Female mosquitoes select specific habitats for oviposition, or the depositing of eggs
- Biotic factors that limit the distribution of a species may include:
- Abiotic factors may also limit distribution.
- Environmental temperature is an important factor in the distribution of organisms because of its effect on biological processes
- Cells may rupture if the water they contain freezes
- Proteins of most organisms denature at temperatures above 45 degrees C.
- Water availability is another important factor.
- Freshwater and marine organisms live submerged in aquatic environments.
- Terrestrial organisms face a nearly constant threat of desiccation
- Sunlight provides the energy that drives all ecosystems, although only plants and other photosynthetic organisms use this energy source directly
- Wind amplifies the effects of environmental temperature on organisms by increasing heat loss due to evaporation and convection
- It also contributes to water loss in organisms by increasing the rate of evaporative cooling and transpiration
- The physical structure, pH, and mineral composition of rocks and soil limit the distribution of plants
- Temperature, water, sunlight, and wind are the major components of climate
- Global climate patterns:
- Earth's curved shape causes latitudinal variation in the intensity of sunlight
- Sunlight strikes the tropics most directly, and the most heat and light are delivered there
- Earth's tilt causes seasonal variation in the intensity of solar radiation.
- June solstice - Northern Hemisphere tilts toward sun; summer begins
- March equinox - equator faces sun directly; 12 hours of daylight and darkness
- December solstice - Northern Hemisphere tilts away from sun; winter begins
- September equinox - equator faces sun directly
- Intense solar radiation near the equator initiates a global pattern of air circulation and precipitation
- Air flowing close to Earth's surface creates predictable global wind patterns
- Macroclimate are patterns on the global, regional, and local level
- Ocean currents influence climate along the coasts of continents by heating or cooling overlying air masses, which may then pass across the land.
- Mountains have a significant effect on the amount of sunlight reaching an area, as well as on local temperature and rainfall.
- In addition to the global changes in day length, solar radiation, and temperature, the changing angle of the sun affects local environments
- During the summer and winter, many lakes in temperate regions are thermally stratified, or layered vertically according to temperature
- Lakes undergo a semiannual mixing of their waters as a result of changing temperature profiles, a process called turnover.
- Microclimate are very fine patterns, such as those encountered by a community underneath a log
- Many features in the environment influence microclimates by casting shade, affecting evaporation from soil, and changing wind patterns.
III. Abiotic and biotic factors influence the structure and dynamics of aquatic biomes
- Biomes are major types of ecological associations that occupy broad geographic regions of land or water
- Aquatic biomes account of the largest part of the biosphere.
- These biomes are physically and chemically stratified
- There is sufficient light for photosynthesis in the upper photic zone
- Little light penetrates in the lower aphotic zone
- At the bottom, the subtrate is called the benthic zone
- It is made up of sand and organic and inorganic sediments
- It is occupied by communities of organisms collectively called benthos
- A major source of food for the benthos is dead organic matter called detritus
- Thermal energy from sunlight warms surface waters to whatever depth the sunlight penetrates.
- In the ocean and in most lakes, a narrow stratum of rapid temperature change called a thermocline separates the more uniformly warm upper layer from more uniformly cold deeper waters
- Major aquatic biomes:
- Lakes are standing bodies of water covering thousands of square kilometers
- Oligotrophic lakes are nutrient poor and generally oxygen rich
- Eutrophic lakes are nutrient rich and often depleted of oxygen if ice-covered in winter and in the deepest zone during summer
- The littoral zone is the shallow, well-lighted waters close to shore
- The limnetic zone is further away from shore and is too deep to support rooted aquatic plants
- A wetland is an area covered with water for a long enough period to support aquatic plants
- The most prominent physical characteristic of streams and rivers is current
- Headwater streams are generally cold, clear, turbulent, and swift
- Rivers are generally warmer and more turbid, since they carry more sediment than their headwaters.
- An estuary is a transition area between river and sea
- They have very complex flow patterns
- An intertidal zone is periodically submerged and exposed by the tides, twice daily on most marine shores
- The oceanic pelagic biome is a vast realm of open blue water, constantly mixed by wind-driven oceanic currents
- Reef building corals are limited to the photic zone of relatively stable tropical marine environments with high water clarity
- A coral reef, which is formed largely from the calcium carbonate skeletons of corals, develops over a long time on oceanic islands
- The marine benthic zone consists of the seafloor below the surface waters of the costal, or neritic, zone and the offshore, pelagic zone.
- Organisms in the very deep benthic or abyssal, zone are adapted to continuous cold and extremely high water pressure
IV. Climate largely determines the distribution and structure of terrestrial biomes
- A climograph is a plot of the temperature and precipitation in a particular region
- Vertical stratification is an important feature of terrestrial biomes
- In many forests, the layers consist of the upper canopy, the low-tree stratum, the shrub understory, the ground layer of herbaceous plants, the forest floor, and the root layer
- Terrestrial biomes usually grade into each other, without sharp boundaries
- The area of intergradation is called an ecotone and may be wide or narrow
- Major terrestrial biomes:
- In tropical rain forests, rainfall is relatively constant, and in tropical dry forests, precipitation is highly seasonal
- Tropical forests are stratified
- Deserts occur in a band near 30 degrees north and south latitude or at other latitudes in the interior of continents
- Precipitation is low and highly variable
- Temperature is variable seasonally and daily
- The savanna is warm year-round, but with somewhat more seasonal variation than in tropical forests
- Chaparral occurs in midlatitude coastal regions on several continents
- It is dominated by shrubs and small trees, along with a high diversity of grasses and herbs
- Temperate grasslands cover parts of South Africa, Hungary, Argentina, Uruguay, Russia, and North America.
- The dominant plants are grasses and forbs
- The northern coniferous forest, or taiga, is the largest terrestrial biome on earth
- Precipitation ranges from 30 to 70 cm, and periodic droughts are common
- Cone-bearing trees dominate these forests
- A mature temperate broadleaf forest has distinct, highly diverse, vertical layers.
- Tundra covers expansive areas of the Arctic, amounting to 20% of Earth's land surface
- A permanently frozen layer of soil called permafrost generally prevents water infiltration.
Ch. 51 (Behavioral Ecology)
I. Behavioral ecology extends observations of animal behavior by studying how such behavior is controlled and how it develops, evolves, and contributes to survival and reproductive success.
II. Behavioral ecologists distinguish between proximate and ultimate causes of behavior.
- Behavior traits are also a part of an animal's phenotype
- It includes muscular as well as nonmuscular activity
- Is everything that an animal does and how it does it.
- Learning is also considered a behavioral process.
- Proximate questions focus on the environmental stimuli that trigger a behavior, as well as the genetic, physiological, and anatomical mechanisms underlying a behavioral act
- These are "how" questions
- Ultimate questions address the evolutionary significance of a behavior
- These are "why" questions
- Ethology is the scientific study of animal behavior, particularly in natural environments.
- Tindenbergen suggested four questions that must be answered to fully understand any behavior
- What is the mechanistic basis of the behavior, including chemical, anatomical, and physiological mechanisms?
- How does development of the animal, from zygote to mature individual, influence behavior?
- What is the evolutionary history of the behavior?
- How does the behavior contribute to survival and reproduction?
- The fixed action pattern is a sequence of unlearned behavioral acts that Is essentially unchangeable and is carried to completion
- A FAP is triggered by an external sensory stimulus known as a sign stimulus
- Imprinting is a type of behavior that includes both learning and innate components and is generally irreversible
- A sensitive period is a limited phase in an animal's development that is the only time when certain behaviors can be learned
III. Many behaviors have a strong genetic component.
- Biologists study the ways both genes and the environment influence development of behavioral phenotypes.
- Nature and nurture
- Innate behaviors are behavior that is developmentally fixed and are under strong genetic influence
- Kinesis is a simple change in activity or turning rate
- Taxis is an oriented movement toward or away from some stimulus.
- Trout automatically swim or orient themselves in an upstream direction, exhibiting rheotaxis
- Bird migration is partly under genetic control.
- Animal communication consists of the transmission of, reception of, and response to signals
- A signal is a behavior that causes a change in another animal's behavior
- It is an essential element of interactions between individuals
- Many animals that communicate through odors emit chemical substances called pheromones
- They are typically very concentrated
- Many animals also communicate by auditory communication
- A variety of mammalian behaviors are under relatively strong genetic control.
- Research has revealed the genetic and neural basis for the mating and parental behavior of male prairie voles.
IV. Environment, interacting with an animal's genetic makeup, influences the development of behaviors.
- Laboratory experiments have demonstrated that the type of food eaten during larval development strongly influences later mate selection by Drosophila mojavensis females
- Cross-fostering studies of California mice and white-footed mice have uncovered an influence of social environment on the aggressive and parental behaviors of mice.
- Learning is the modification of behavior based on specific experiences.
- Special learning is the modification of behavior based on experience with the special structure of the environment
- This makes use of landmarks, or location indicators
- A cognitive map is an internal representation or code of the spatial relationships between objects in an animal's surroundings
- Associative learning is the ability of many animals to associate one feature of the environment with another
- Classical conditioning is a type of associative learning in which an arbitrary stimulus is associated with a reward or punishment
- operant conditioning is called trial-and-error learning
- Cognition is the ability of an animal's nervous system to perceive, store, process, and use information gathered by sensory receptors.
- The study of animal cognition, called cognitive ethology, examines the connection between an animal's nervous system and its behavior.
- Habituation is a loss of responsiveness to stimuli that convey little or no information
V. Behavioral traits can evolve by natural selection.
- When behavioral variation within a species corresponds to variation in environmental conditions, it may be evidence of past evolution
- An example of genetically based variation in behavior within a species is pretty selection by the garter snake Thamnophis elegans
- Foraging is behavior associated with recognizing, searching for, capture, and consuming food
- Laboratory studies of Drosophila populations raised in high and low density conditions show a clear divergence in behavior linked to specific genes
- D. melangogaster living at low population density followed a foraging path shorter than that of D. melanogaster living at high population density
VI. Natural selection favors behaviors that increase survival and reproductive success.
- Optimal foraging theory states that natural selection should favor foraging behavior that minimizes the costs of foraging and maximizing the benefits.
- How mate choice enhances reproductive success varies, depending on the species' mating system.
- In promiscuous mating, there are no strong pair bonds or lasting relationships
- In monogamous mating, one male mates with one female
- In polygamous mating, an individual of one sex mates with several of the other
- In polygyny, one males mates with many females
- In polyandry, one female mates with several males
- Males competition for mates is a source of intrasexual selection that can reduce variation among males
- agonistic behavior is an often ritualized contest that determines which competitor gains access to a resource, such as food or mates
- Game theory provides a way of thinking about evolution in situations where the fitness of a particular behavioral phenotype is influenced by other behavioral phenotypes in the population.
VII. The concept of inclusive fitness can account for most altruistic social behavior.
- On occasion, animals behave in altruistic ways that reduce their individual fitness but increase the fitness of the recipient of the behavior.
- For example, if a squirrel sees a predator approach, the squirrel gives off an alarm, alerting unaware individuals but increasing the risk to itself
- This behavior can be explained by the concept of inclusive fitness
- It is the total effect an individual has on proliferating its genes by producing its own offspring and by providing aid that enables other close relatives to produce offspring
- The three key variables in an act of altruism are the benefit to the recipient (B), the cost to the altruist (C), and the coefficient of relatedness (r).
- Hamilton's rule states that rB > C
- Kin selection favors altruistic behavior by enhancing the reproductive success of relatives
- Altruistic behavior toward unrelated individuals can be adaptive if the aided individual returns the favor in the future, an exchange of aid called reciprocal altruism.
- Social learning forms the roots of culture, which can be defined as a system of information transfer through observation or teaching that influences the behavior of individuals in a population.
- Male choice copying is a behavior in which individuals in a population copy the mate choice of others
- Human culture is related to evolutionary theory in the discipline of sociobiology, whose main premise is that certain behavior characteristics exist because they are expressions of genes that have been perpetuated by natural selection.
I. Population ecology is the study of populations in relation to the environment, including environmental influences on population density and distribution.
- A population is a group of individuals of a single species living in the same general area
II. Dynamic biological processes influence population density, dispersion, and demography.
- Population density, the number of individuals per area or volume, results from the combination of births, deaths, immigration, and emigration.
- Dispersion is the pattern of spacing among individuals within the boundaries of the population
- Environmental and social factors influence the spacing of individuals
- In clumped patterns, individuals are aggregated in patches
- In uniform patterns, individuals are evenly spaced
- Animals often exhibit uniform dispersion as a result of antagonistic social interactions, such as territoriality, the defense of a bounded physical space against encroachment by other individuals
- In random dispersion, individuals are unpredictably spaced, and the position of each individual is independent of others
- This occurs in the absence of strong attraction or repulsions among individuals of a population
- Populations grow from births and immigration and shrink from deaths and emigration
- Immigration is the influx of new individuals from other areas
- Emigration is the movement of individuals out of a population
- Demography is the study of the vital statistics of populations and how they change over time
- Of particularly interest to demographers are birth rates and how they vary among individuals and death rates
- Life tables are age-specific summaries of the survival pattern of a population
- the best way to construct one is to follow the fate of a cohort, a group of individuals of the same age, from birth until all are dead
- A survivorship curve is a plot of the proportion or numbers in a cohort still alive at each age
- Idealized survivorship curves:
- Type I curve is flat at the start, reflecting low death rates during early and middle life, then drops steeply as death rates increase among older age groups
- Type II curves are intermediate, with a constant death rate over the organism's life span
- Type III curve drops sharply at the start, reflecting very high death rates for the young, but the flattens out as death rates decline for those individuals that have survived to a critical age
- Reproductive tables, or fertility schedules, are age specific summaries of the reproductive rates in a population
III. The traits that affect an organism's schedule of reproduction and survival from birth through reproduction to death make up its life history.
- They are evolutionary outcomes reflected in the development, physiology, and behavior of an organism.
- Semelparous organisms reproduce a single time and die.
- When the survival rate of offspring is low, as in highly variable or unpredictable environments, this is favored
- Iteroparous organisms produce offspring repeatedly.
- When environments are dependable and where competition for resources may be intense, this is favored.
- Life history traits such as brood size, age at maturity, and parental caregiving represent trade-offs between conflicting demands for limited time, energy, and nutrients.
IV. The exponential model describes population growth in an idealized, unlimited environment.
- The per capita birth rate (b) is the number of offspring produced per unit time by an average member of the population
- The per capita death rate (m) is the number of individuals of a population that die per unit time
- The per capita rate of increase (r), or a population's growth rate, equals birth rate minus death rate.
- R = b - m
- Growth occurs when r>0 and decline occurs when r<0
- Zero population growth occurs when the per capita birth and death rates are equal (r = 0)
- Exponential population growth is population increase under the ideal conditions of abundant food and the freedom to reproduce at physiological capacity
- Under these conditions, the per capita rate of increase may assume the maximum rate for the species, called the intrinsic rate of increase and denoted as rmax
- The exponential growth equation dN/dt = rmaxN represents a population's potential growth in an unlimited environment. dN denotes change in population, while dt denotes change in time
V. The logistic growth model includes the concept of carrying capacity.
- Carrying capacity (K) is the maximum population size that a particular environment can support
- It is not fixed, but varies over space and time with the abundance of limiting resources
- Exponential growth cannot be sustained for long in any population.
- A more realistic population model limits growth by incorporating carrying capacity
- According to the logistic equation dN/dt = rmaxN (K - N)/K, growth levels off as population size approaches the carrying capacity.
- The logistic model fits few real populations, but it is useful for estimating possible growth.
- K-selection is density-dependent selection
- r-selection is density-independent selection
VI. Populations are regulated by a complex interaction of biotic and abiotic influences.
- In density-dependent population regulation, death rates rise and birth rates fall with increasing density
- In density-independent regulation, birth and death rates do not change with increasing density.
- Density-dependent changes in birth and death rates curb population increase through negative feedback and can stabilize a population near its carrying capacity.
- Limiting factors include intraspecific competition for limited food or space, increased predation, disease, stress due to crowding, and buildup of toxins.
- Because changing environmental conditions periodically disrupt them, all populations exhibit some size fluctuations.
- The study of population dynamics focuses on the complex interactions between biotic and abiotic factors that cause variation in population size
- Immigration and emigration influences populations more when a group of populations is linked, forming a metapopulation.
VII. Human population growth has slowed after centuries of exponential increase
- Since 1650, the global human population has grown exponentially, but within the last 40 years, the rate of growth has fallen by nearly 50%
- Currently the global population numbers over 6 billion
- It is increasing by about 73 million each year
- Two possible configurations for a stable population are:
- Zero population growth = high birth rate - high death rate
- Zero population growth = low birth rate - low death rate
- The movement toward the second state is called the demographic transition
- Differences in age structure show that while some nations are growing rapidly, others are stable or declining in size.
- One important demographic variable in present and future growth trends is a country's age structure, the relative number of individuals of each age
- Infant mortality is the number of infant deaths per 1000 live births and life expectancy at birth, the predicted average length of life at birth, vary widely among human populations
- The ecological footprint concept summarizes the aggregate land and water area appropriated by each nation to produce al the resources it consumes and to absorb all the waste it generates
- The ecological capacity is the actual resource base of each country
- The U.S. is already above carrying capacity
Ch. 53 (Community Ecology)
I. A community is an assemblage of populations of various species living close enough for potential interaction is called a biological community.
II. A community's interactions include competition, predation, herbivory, symbiosis, and disease.
- Populations are linked by interspecific interactions that affect the survival and reproduction of the species engaged in the interaction.
- Interspecific competition occurs when species compete for a particular resource that is in short supply.
- Strong competition can lead to the local elimination of one of the two competing species, a process called competitive exclusion
- The sum total of a species' use of the biotic and abiotic resources in its environment is called the species' ecological niche
- The niche concept can be used to restate the competitive exclusion principles into "two species cannot coexist in a community if their niches are identical"
- The differentiation of niches that enables similar species to coexist in a community is called resource partitioning
- The tendency for characteristics to be more divergent in sympatric (geographically overlapping) populations of two species than in allopatric (geographically separate) populations of the same two species is called character displacement
- Predation refers to a (+/-) interaction in which one species, the predator, kills and eats the other, the prey.
- Cryptic coloration, or camouflage, makes prey difficult to spot and is a morphological and physiological defensive adaptation.
- Animals with effective chemical defenses often exhibit bright warning coloration, or aposematic coloration.
- Mimicry is another example of defensive adaptations
- In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model
- In Mullerian mimicry, two or more unpalatable species resemble each other
- Herbivory, a (+/-) interaction in which an herbivore eats parts of a plant or an alga, has led to the evolution of various chemical and mechanical defenses in plant species as well as consequent adaptations by herbivorous species.
- In parasitism, one organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process.
- Parasites that live within the body of their host are called endoparasites
- Parasites that feed on the external surface of a host are called ectoparasites
- In parasitoidism, insects lay eggs on or in living hosts
- The effects of disease causing agents known as pathogens on populations and communities are similar to that of parasites.
- Mutualism is an interspecific interaction that benefits both species (+/+)
- In commensalisms, one species benefits and the other is not affected (+/0)
- There are few cases of pure commensalisms.
- Generalized adaptation of organisms to other organisms in their environment is a fundamental feature of life.
- Coevolution is reciprocal evolutionary adaptations of two interacting species
- This linkage of adaptations requires that genetic change in one of the interacting populations of the two species be tied to genetic change in the other population.
III. Dominant and keystone species exert strong controls on community structure.
- The species diversity, which is the variety of different kinds of organisms that make up the community, has two components
- Species richness is the total number of different species in the community
- Relative abundance is the proportion each species represents of the total individuals in the community
- A community with an even species abundance is more diverse than one in which one or two species are abundant and the remainder rare.
- Trophic structure, which is the extent on the feeding relationships between organisms, is a key factor in community dynamics.
- Food chains link the trophic levels from producers to top carnivores.
- A chain is comprised of several trophic levels:
- Photosynthetic organisms (primary producers)
- Herbivores (primary consumers)
- Carnivores (secondary and tertiary consumers)
- Branching food chains and complex trophic interactions form food webs.
- The energetic hypothesis suggests that the length of a food chain is limited by the inefficiency of energy transfer along the chain and predicts that food chains should be relatively longer in habitats of higher photosynthetic productivity
- The dynamic stability hypothesis proposes that long food chains are less stable than short chains and predicts that food chains should be shorter in unpredictable environments
- Dominant species and keystone species exert strong controls on community structure.
- Dominant species are the most abundant species in a community, and their dominance is achieved by having high competitive ability.
- They have the highest biomass, which is the total mass of all individuals in a population
- Invasive species, species that take hold outside their native range can attain high biomass in environments lacking their natural predators and pathogens.
- Keystone species are usually less abundant species that exert a disproportionate influence on community structure because of their ecological niche.
- Ecosystem engineers, also called foundation species, exert influence on community structure through their effects on the physical environment.
- By altering the structure or dynamics of the environment, foundation species act as facilitators that have positive effects on the survival and reproduction of some of the other species in the community
- The bottom-up model proposes a unidirectional influence from lower to high trophic levels, in which nutrients and other abiotic factors are the main determinates of community structure, including the abundance of primary producers.
- The top-down model proposes that control of each trophic level comes from the trophic level above, with the result that predators control herbivores, which in turn control primary producers.
- Because many freshwater lake communities seem to be structured according to this model, ecologists have a potential means of improving water quality
- This strategy, called biomanipulation, changes the abundance of the top consumer so that other organisms lower down the trophic food chain can clear the pollution
IV. Disturbance influences species diversity and composition.
- Evidence suggests that disturbance and nonequilibrium rather than stability and equilibrium are the norm for most communities
- The nonequilibrium model describes communities as constantly changing after being buffeted by disturbances
- According to the intermediate disturbance hypothesis, moderate levels of disturbance can foster higher species diversity than can low or high levels of disturbance.
- Humans are the most widespread agents of disturbance, and their disturbance to communities usually reduces species diversity.
- Ecological succession is the sequence of community and ecosystem changes after a disturbance.
- Primary succession occurs where no soil exists when succession begins.
- Secondary succession begins in an area where soil remains after a disturbance.
- Mechanisms producing community change during succession include facilitation and inhibition.
- Early arrivals may facilitate the appearance of the later species by increasing the fertility of the soil
- Early arrivals may inhibit the appearance of the later species
- Early arrivals may be completely independent of the later of the later species, which tolerate conditions created
V. Biogeographic factors affect community biodiversity.
- Species richness generally declines along an equatorial polar gradient and is especially great in the tropics.
- Climate is likely the primary cause of the latitudinal gradient in biodiversity
- A community's rate of evapotranspiration is the evaporation of water from soil plus the transpiration of water from plants
- Actual evapotranspiration is determined by the amount of solar radiation, temperature, and water availability
- Potential evapotranspiration is a measure of energy availability but not water availability and is determined by the amount of solar radiation and temperature
- Species richness is directly related to a community's geographic size, a principle formalized in the species-area curve.
- Species richness on islands depends on island size and distance from the mainland.
- The equilibrium model of island biogeography maintains that species richness on an ecological island levels off at some dynamic equilibrium point, where new immigrations are balanced by extinctions.
VI. Contrasting views of community structure are the subject of continuing debate.
- The integrated hypothesis states that the species within a community are locked into particular biotic interactions.
- The rivet model suggests that all the species in a community are linked together in a tight web of interactions, so that the loss of even a single species has strong repercussions for the community.
- The individualistic hypothesis proposes that communities are loosely organized associations of independently distributed species with the same abiotic requirements.
- The redundancy model proposes that most of the species in a community are not tightly associated with one another and that if a species is lost from a community, other species will fill the gap.
Ch. 54 (Ecosystems)
I. Ecosystem ecology emphasizes energy flow and chemical cycling.
- An ecosystem consists of all the organisms in a community and all the abiotic factors with which they interact.
- The laws of physics and chemistry apply to ecosystems, particularly in regard to the flow of energy.
- The principle of conservation of energy states that energy cannot be created or destroyed but only transformed
- The second law of thermodynamics is that energy conversions cannot be completely efficient, as some energy is always lost as heat in any conversion process
- Energy flows through an ecosystem, entering as light and exiting as heat
- Nutrients cycle within an ecosystem
- Energy and nutrients pass through multiple trophic levels
- Primary producers are the trophic level that ultimately supports all others (autotrophs)
- Primary consumers (herbivores that eat autotrophs)
- Secondary consumers (carnivores that eat herbivores)
- Tertiary consumers (carnivores that eat carnivores)
- Decomposition connects all trophic levels.
- Detrivores, or decomposers, mainly bacteria and fungi, recycle essential chemical elements by decomposing detritus, which is dead organic material, and returning elements to inorganic reservoirs.
II. Physical and chemical factors limit primary production in ecosystems.
- The energy assimilated during photosynthesis is a tiny fraction of the solar radiation reaching earth, but primary production sets the spending limit for the global energy budget.
- Primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period
- Gross primary production is the total energy assimilated by an ecosystem in a given time period.
- Net primary production, the energy accumulated in autotroph biomass, equals gross primary production minus the energy used by the primary producers for respiration.
- Tropical rain forests are among the most productive terrestrial ecosystems and contribute a large portion of the planet's overall net primary production
- The open ocean contributes more net primary production than any other single ecosystem, due to its very large size
- net primary production per unit area is relatively low
- In marine and freshwater ecosystems, light and nutrients limit primary production.
- A limiting nutrient is the element that must be added in order for production to increase in a particular area
- Within the photic zone, the factor that most often limits primary production is a nutrient such as nitrogen, phosphorus or iron.
- Eutrophication is the process by which sewage and fertilizer runoff from farms and yards added large amounts of nutrients to lakes, resulting in cyanobacteria becoming dominant and in the death of all but the most tolerant fish species
- In terrestrial and wetland ecosystems, climatic factors such as temperature and moisture affect primary production on a large geographic scale.
- A soil nutrient is often the limiting factor in primary production.
III. Energy transfer between trophic levels is usually less than 20% efficient.
- Net secondary production is the energy stored in biomass represented by growth and reproduction.
- Production efficiency is the fraction of energy stored in food that is not used for respiration
- The amount of energy available to each trophic level is determined by the net primary production and the efficiencies with which food energy is converted to biomass at each link of the food chain.
- The percentage of energy transferred from one trophic level to the next, called trophic efficiency, is generally 5-20%.
- According to the green world hypothesis, herbivores consume a small percentage of vegetation because predators, disease, competition, nutrients limitations, and other factors keep their populations in check.
- Plants have defenses against herbivores
- Nutrients, not energy supply, usually limit herbivores
- Abiotic factors limit herbivores
- Intraspecific competition can limit herbivore numbers
- Interspecific interactions keep herbivore densities in check
IV. Biological and geochemical processes move nutrients between organic and inorganic parts of the ecosystem.
- Gaseous forms of carbon, oxygen, sulfur, and nitrogen occur in the atmosphere and cycle globally.
- Other less mobile elements, including phosphorus, potassium, and calcium, cycle on a more localized scale, at least over the short term.
- Biogeochemical cycles:
- Water moves in a global cycle driven by solar energy.
- The carbon cycle primarily reflects the reciprocal processes of photosynthesis and cellular respiration.
- Nitrogen enters ecosystems through atmospheric deposition and nitrogen fixation by prokaryotes, but most of the nitrogen cycling in natural ecosystems involves local cycles between organisms and soil or water.
- The proportion of a nutrient in a particular form and its cycling time in that form vary among ecosystems, largely because of differences in the rate of decomposition.
- Nutrient cycling is strongly regulated by vegetation.
V. The human population is disrupting chemical cycles throughout the biosphere
- Agriculture constantly removes nutrients from ecosystems, so large supplements are continually required.
- Considerable amounts of the nutrients in fertilizer pollute groundwater and surface-water aquatic ecosystems, where they can stimulate excess algal growth, a process called cultural eutrophication.
- Critical load is the amount of added nutrient that can be absorbed by plants without damaging ecosystem integrity
- Combustion of fossil fuels is the main cause of acid precipitation.
- North American and European ecosystems downwind from industrial regions have been damaged by rain and snow containing nitric acid and sulfuric acid.
- Toxins can become concentrated in successive trophic levels of food webs, a process called biological magnification.
- The release of toxic wastes has polluted the environment with harmful substances that often persist for long periods of time and become concentrated along the food chain by biological magnification.
- Because of the burning of wood and fossil fuels and other human activities, atmospheric concentration of CO2 has been steadily increasing.
- The ultimate effects may include significant warming and other climate change due to the greenhouse effect
- The process by which carbon dioxide and water vapor in the atmosphere intercept and absorb much of the reflected infrared radiation from the sun, re-reflecting some of it back toward Earth, resulting in the retention of some of the solar heat, is called the greenhouse effect
- The ozone layer reduces the penetration of UV radiation through the atmosphere.
- Human activities, including release of chlorine containing pollutants, are eroding the ozone layer, with dangerous results.
Ch. 55 (Conservation Biology and Restoration Ecology)
I. Conservation biology integrates ecology, physiology, molecular biology, genetics, and evolutionary biology to conserve biological diversity at all levels.
II. Restoration ecology applies ecological principles in an effort to return degraded ecosystem to conditions as similar as possible to their natural predegraded state.
III. Human activities threaten Earth's biodiversity.
- Biodiversity consists of the varied ecosystems in the biosphere, the species richness within those ecosystems, and the genetic variation within and among populations of each species.
- The U.S. Endangered Species Act defines an endangered species as one that is in danger of extinction throughout all or a significant portion of its range
- Threatened species are those thatare considered likely to become endangered in the foreseeable future
- Our biophilia enables us to recognize the value of biodiversity for its own sake.
- Ecosystem services encompass all the processes through which natural ecosystems and the species they contain help sustain human life on earth.
- Some ecosystem services:
- Purification of air and water
- Reduction of the severity of droughts and floods
- Generation and preservation of fertile soils
- Detoxification and decompositions of wastes
- The four major threats to biodiversity:
- Habitat destruction is the single greatest threat to biodiversity throughout the biosphere
- Introduced species, also called invasive, nonnative, or exotic species
- Overexploitation refers generally to the human harvesting of wild plants or animals at rates exceeding the ability of populations
- Disruption of interaction networks
IV. Population conservation focuses on population size, genetic diversity, and critical habitat.
- Conservation biologists who adopt the small population approach study the processes that can cause very small populations finally to become extinct
- When a population drops below a minimum viable population (MVP) size, its loss of genetic variation due to nonrandom mating and genetic drift can trap it in an extinction vortex.
- The minimum viable population of a population is factored into what is called a population viability analysis, the objective of which is to reasonably predict a population's chances for survival
- A meaningful estimate of MVP requires the researcher to determine the effective population size, which is based on the breeding potential of the population.
- The declining population approach focuses on the environmental factors that cause decline, regardless of absolute population size.
- Steps for analyzing declining populations and determining interventions are useful even in complex cases:
- Asses population trends and distribution to confirm that the species is presently in decline or that it was formerly more widely distributed or more abundant
- Study the natural history of this and related species, including reviewing the research literature, to determine the species' environmental requirements
- Develop hypotheses for all possible causes of the decline, including human activities and natural events, and list the predictions of each hypothesis
- Because many factors may be correlated with the decline, test the most likely hypothesis first.
- Apply the results of the diagnosis to management of the threatened species and monitor recovery
- Conserving species often requires resolving conflicts between the habitat needs of endangered species and human demands.
V. Landscape and regional conservation aim to sustain entire biotas.
- One goal of landscape ecology is to understand past, present, and future patterns of landscape use and to make biodiversity conservation part of land-use planning
- The structure of a landscape can strongly influence biodiversity.
- As habitat fragmentation increases and edges become more extensive, biodiversity tends to increase.
- Movement corridors can promote dispersal and help sustain populations.
- a movement corridor is a narrow strip or series of small clumps of quality habitat connecting otherwise isolated patches
- Biodiversity hot spots are also hot spots of extinction and thus prime candidates for protection.
- Sustaining biodiversity in parks and reserves requires management to ensure that human activities in the surrounding landscape do not harm the protected habitats.
- The zoned reserve model recognizes that conservation efforts often involve working in landscapes that are largely human dominated.
- A zoned reserve is an extensive region of land that includes one or more areas undisturbed by humans surrounded by lands that have been changed by human activity and are used for economic gain
VI. Restoration ecology attempts to restore degraded ecosystems to a more natural state.
- In bioremediation, restoration ecologists are harnessing living organisms to detoxify polluted ecosystems.
- In biological augmentation, ecologists also use organisms to add essential materials to ecosystems.
- The newness and complexity of restoration ecology require scientists to consider alternative solutions and adjust approaches based on experience.
VII. Sustainable development seeks to improve the human condition while conserving biodiversity.
- The goal of the Sustainable Biosphere Initiative is to acquire the ecological information needed for the development, management, and conservation of Earth's resources.
- Costa Rica's success in conserving tropical biodiversity has involved partnerships between government, other organizations, and private citizens.
- Our innate sense of connection to nature may eventually motivate a realignment of our environmental priorities.
1. Ecology is the scientific study of the interactions between organisms and the environment, whereas environmentalism is advocating for the protection or preservation of the natural environment. Ecology provides the understanding necessary to address environmental problems.
2. An event that occurs on the ecological time scale can affect events that occur on an evolutionary time scale by altering the gene pool of organisms.
3. In population ecology, an ecologist might study the distribution and abundance of red kangaroos in Australia. In community ecology, an ecologist might study changes in which plant species are most abundant in a forest following a wildfire.
1. Human actions that could expand a species' distribution by changing its dispersal would be the transplanting of species. Human actions that could expand a species' distribution by changing its biotic interactions would be the removal or predators or the addition of prey.
2. The sun's unequal heating of Earth's surface influence global climate patterns by distributing heat unevenly across the earth, resulting in varying temperatures and amount of light. In addition to that, it could initiate a global pattern of air circulation and precipitation.
1. Stoneflies are more likely to live in oligotrophic lakes, due to the high concentrations of oxygen.
2. Phytoplankton, and not benthic algae or rooted aquatic plants, are the dominant photosynthetic organisms of the oceanic pelagic biome because the benthic zone is too deep for light to effectively reach, resulting in a lower or absent rate of photosynthesis in the benthic zone.
1. Deserts typically have a higher annual average temperature than dry tundra.
2. The natural biome in which I live is a desert. The temperature varies, ranging from very hot at noon to very cold at night. There are a variety of animals and plants, but most of the plants are dry and there is not an abundance of them. However, these do not reflect my actual surroundings, as I live in house, which maintains an environment separate from the outside environment.
1. How does the squirrel make that brief, loud call? (proximate) How does development influence this call? (proximate) Why does the squirrel make the sound? (ultimate) Why does this increase the squirrels' survival and fitness? (ultimate)
2. This behavior is an example of fixed action pattern. A proximate explanation is that the rolling of the egg acts as a sign stimulus that causes the mother to nudge the egg back into the nest. An ultimate explanation is that it will increase the specie's fitness, if more offspring survive.
1. Both nature and nurture have great influence on thee development of behaviors, and neither exerts dominance over the other as they work in unison.
2. An example of how researchers study whether a particular behavior has a strong genetic component is the lacewing species experiment. Scientists took two morphologically identical species of lacewings that sing different courtship songs and cross-bred them. The hybrid offspring sung a song similar to both parents, suggesting that the songs are under genetic control.
1. Cognitive maps can increase an animal's capacity to learn spatial relationships by allowing animals to develop an internal representation of the spatial relationships between objects in the animal's surrounding.
2. Three ways in which an animal's environment can influence the development of its behavior are its diet, society, and learning.
3. Associative learning might explain why unrelated distasteful or stinging insects because due to learning, predators would avoid insects with the colors associated with bad taste or a sting. Natural selection would favor those insects with those colors, while other insects would be eaten, even though they themselves have a bad taste or sting, because predators did not form the association.
1. Geographic variation in garter snake foraging behavior might demonstrate that the behavior evolved by natural selection because depending on food availability, natural selection would select for individuals that utilized the available food. In coastal regions, where banana slugs were available, natural selection would select for snakes that would eat the slugs.
2. Hedrick and Riechert examined behavioral variation between populations of both laboratory-raised spiders and wild ones to show that their differences in aggressiveness are due to genetic differences between the populations, and not the environment alone.
3. The conclusions that Berhold and his colleagues drew from their studies of blackcap migratory patterns are that migratory orientation in blackcaps has a genetic basis, since laboratory-raised offspring of both British and German blackcaps showed different migratory orientations.
1. Male parental care is more likely to evolve among species with external fertilization than among species with internal fertilization because certainty of paternity is higher with external fertilization.
2. Optimal foraging theory explains why mule deer spend more time foragi
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