Ecology and the Biosphere
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Published: Tue, 06 Feb 2018
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.
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