Ecology (16-17%)
Net Ecosystem Production (NEP)
Measure of total biomass accumulation during a given period of time. NEP=GPP-Rt Rt accounts for decomposers and other heterotrophs. NEP determines whether an ecosystem is gaining or losing carbon over time. Limiting Nutrient- element that must be added for production to increase. Eutrophication- primary producers die, detritivores decompose them, depleting water of much of its oxygen.
Dispersal of Cattle Egret
Native to Africa, Cattle Egrets first recorded in South America in 1877. Long distance dispersal can lead to adaptive radiation , the rapid evolution of an ancestral species into a new species that fill many ecological niches.
Diversity and Community Stability
Benefits of diversity= increased productivity and stability of biological communities. Most diverse plots of habitat consistently produce more biomass (total mass of all organisms in a habitat) than a single-species plot. Higher-diversity communities are often more resistant to invasive species.
Global Climate Change
Earth has warmed on average of 1.6F since 1900 and should warm another 2-11F by 2100.
Exploitation: Herbivory
Herbivory (+/-)- herbivore eats a plant. Herbivores have many adaptations (and so do plants to avoid being eaten).
Metapopulation
Immigration and Emigration are particularly important when a number of local populations are linked, forming a meta population. Local populations occupy patches of suitable habitat in a "sea" of unsuitable habitat. Patches vary in size, quality, and isolation from other patches, factors that influence how many individuals move among the populations. If one population becomes extinct its patch can be occupied by immigrants from another. Provides a framework for conservation of species living in a network of habitat fragments and reserves.
Species Diversity
Species diversity-variety of different kinds of organisms that make up one community- has two components. 1.) Species richness- number of different species in the community. 2.) Relative abundance- of different species, the proportion each species represents of all individuals in the community. Two forests, four species of trees with 100 individuals each. Forest 1: 25A, 25B, 25C, 25D- MORE DIVERSE. Forest 2: 80A, 5B, 5C, 10D Species richness is the same for both forests (same number of species), but relative abundance is very different.
Shannon Diversity (H)
Tool to compare diversity of communities across time and space. H= - (pa ln pa + pb ln pb+ pc ln pc +........) A, B, C are the species in the community. P is the relative abundance of each species. ln is the natural Logarithm. ln of each value of p can be determined using the "ln" key on a scientific calculator. Higher value of H indicates a more diverse community. Forest 1, p =0.25 for each of the four species, so H= -4(0.25 ln 0.25) = 1.39 Forest 2, H= - [0.8 ln 0.8 + 2 (0.05 ln 0.0.5) + 0.1 ln 0.1]= 0.71
Trade-Offs
Trade off between offspring number and the amount of resources a parent can devote to each offspring. Such trade-offs occur because organisms to not have access to unlimited amounts of resources. As a result, use of resources for one function (such as reproduction) can reduce the resources available for supporting other functions (like survival). Selective pressures also influence trade offs between number and size of offspring. Plants/animals whose young have a low chance of survival will produce many small offspring.
Microclimate
Very fine, localized patterns in climactic conditions.
Bottom-Up Controls
Ways in which adjacent trophic levels affect one another. (V-vegetation, H- herbivores). V--->H: increase in vegetation will increase number or biomass of herbivores (not vice versa) V<---H: Increase in herbivore biomass will decrease vegetation. V<--->H: herbivores/vegetation sensitive to changes in biomass of the other Two models: 1.) Bottom-up model (V--->H): Unidirectional influence from producers to consumers N(nutrient)-->V(vegetation)-->H--->P (predator). If you add mineral nutrients to stimulate plant growth, higher trophic levels should also increase in biomass.
Niche Influenced by Interspecific Competition
Yes! In this study (of two barnacle species) biologist removed one and the other took over its spot. Interspecific competition reduces niche size
Mountains
1.) Cool air flows inland from water, moderating temperatures near shore 2.) Air that encounters mountains flows upward, cools at higher altitudes, and releases water as precipitation. 3.) Less moisture is left in the air reaching the leeward side, which there for has little precipitation. The rain shadow can create a desert on the back side of the mountain range.
Seasonal Turnover in Lakes with Winter Ice Cover
1.) In winter coldest water lies just below the surface ice, water gets progressively warmer as you go deeper. 2.) In spring, surface water warms and mines with layers below, eliminating thermal stratification. Spring winds mix the water. 3.) In summer lake regains thermal profile, warm surface water becomes separated from cold bottom water. 4.) In autumn, surface water cools rapidly and sinks beneath underlying layers, remixing water until surface beings to freeze and temperature profile is reestablished. *turnover- sends oxygenated water from a lake's surface to the bottom and brings nutrient rich water from the bottom to the surface in spring/autumn.
Changes in Soil Nitrogen Content During Succession
1. Pioneer species 2. Dryas 3. Alder 4. Spruce
Survivorship Curves
A plot of the proportion or numbers in a cohort still alive at each age. Straight line= constant rate of death. Though diverse, survivorship curves can be classified into three general types. 1.) Type I curve, flat at the start, reflecting low death rates during early and middle life, then drops steeply. 2.) Type III curve drops sharply at the start, reflecting high death rates for the young, but flattens out as the rates decline for the few individuals that survived early die off. 3.) Type II curve- Death fairly constant. In populations not experiencing large amounts of immigration or emigration survivorship is one of the two key factors determining changes in population size. The other is the reproductive rate.
Primary Production
Amount of light energy converted to chemical energy in an ecosystem by autotrophs. Gross and Net Production: Gross Primary Production (GPP)- amount of energy from light converted to chemical energy of organic molecules per unit time. Net Primary production (NPP)- equal to GPP- energy used by autotrophs (primary producers). NPP=GPP-Ra (a stands for autotroph). On average NPP is about 1/2 GPP. NPP represents storage of chemical energy available to consumers in an ecosystem.
Ecological Change and Evolution
An ecological change, such as the expansion of a predators range, can alter selective pressures faced by prey populations. This could cause evolutionary change, such as an increase in the frequency of a new defense mechanism in a prey population; that change, in turn, could alter outcome of ecological interactions.
Animal Production Efficiencies
Birds and mammals have low production efficiencies in the range of 1-3% because they use so much energy maintaining constant, high body temp. Fish (ectotherms) have efficiencies around 10% Insects/microorganisms around 40% or more.
Carbon Cycle
Carbon forms framework of all organic molecules. Photosynthetic organisms utilize CO2 and convert to organic forms/sugars. Reservoirs of carbon are fossil fuels, soils, sediments of aquatic ecosystems, oceans, plant and animal biomass, and the atmosphere. Largest reservoir is sedimentary rocks like limestone. All organisms return CO2 to environment directly via respiration
Logistic Growth Model
Carrying capacity- Symbolized by K, as the maximum population size that a particular environment can sustain. Logistic population growth- per capita rate of population growth approaches zero as the population size nears carrying capacity (K). dN/dt= rN((K-N)/K) when N is small compared to K, the term (K-N)/K is close to 1.
Changes in Population Size
Changes= Birth + immigrants - deaths - emigrants ΔN/Δt= B-D N= population size t= time Δ= change B= births D= deaths ΔN/Δt=R where R= difference between births/deaths dN/dt= rN Intrinsic rate of increase (r)- per captain rate at which an exponentially growing population increases in size at each instant in time.
Secondary Production
Chemical energy in consumers' food that is converted to their own new biomass during a given period. Most of an energy systems production consumed by detritivores. Production efficiency= (Net Secondary production x 100%)/(Assimilation of primary production). *Percentage of energy stored in assimilated food that is used for growth, and reproduction (NOT respiration). Assimilation consists of total amount of energy an organism has consumed and used for growth, reproduction, and respiration. For caterpillar production efficiency is 33%; 67J of the 100J of assimilated energy is used for respiration.
Patterns of Dispersion
Clumped- most common pattern dispersal, individuals aggregated into patches. Plants and fungi are often clumped where soil conditions favor germination and growth. Can also be associated with mating behaviors. Aggregation of individuals may also increase effectiveness of predators or defense. Uniform- evenly spaced pattern of dispersion may result from direct interactions between individuals in the population. Often exhibited as a result of antagonistic social interactions, such as territoriality. Random- unpredictable spacing, position of each individual in a population is independent of other individuals. Occurs in the absence of strong attractions or repulsions among individuals where key physical or chemical factors are relatively constant (ie. dandelions distributed randomly in a fairly uniform habitat)
Positive Interactions: Commensalism
Commensalism (+/0)- benefits one, but doesn't help or harm the other. Ie. cattle egrets feed on insects flushed out of grass by grazing bison. Because the birds increase their feeding rates when following the herbivores, they benefit from the association. The herbivores are not affected by the birds. However, ecological interactions can change over time. Birds may eat parasites off of cattle or even warn them when predators are coming. Commensalism interaction (+/0) can often become a +/+ Mutualism interaction.
Mechanisms of Density-Dependent Regulation
Competition for resources Disease Predation Territoriality- presence of surplus or non breeding animals is a good indication that territoriality is restricting population growth Intrinsic factors- Drop in reproduction at high density is associated with aggressive interactions and hormonal changes that delay sexual maturation and depress the immune system. Toxic waste *all reduce reproductive rates*
Density and Dispersion
Density of a population is the number of individuals per unit area or volume. Dispersion is the pattern of spacing among individuals within the boundaries of the population. Population size and density can be determined by counting all individuals within the boundaries of the population (all sea stars in a tide pool, counting members of elephant herd). Not always possible, so instead ecologists use sampling techniques (i.e.. how many trees in a 100m x 100m plot, calculate average density of the plot and extend to estimate entire population). Ecologists also measure density using an indicator of population size (number of nests, burrows, tracks, or fecal droppings). Mark-recapture method also used to estimate size of populations.
Demographics
Demography- study of death, birth, and migration rates within a population and how they change over time. Life table- summarizes survival and reproductive rates of individuals in specific age-groups within a population. To construct, researchers follow fate of a cohort, a group of individuals of the same age, from birth until death. Demographers often ignore males and study females because only females produce offspring. Population is viewed in terms of females giving rise to new females.
Population Change and Population Density
Density independent (temperature, precipitation)- A birth rate or death rate that does not change with population density. Can cause dramatic changes in population size (ie. drought or heat wave). Density dependent- a death rate that increase with population density or a birth rate that falls with rising density. *only density dependent factor can cause population to decrease in size when it is large, or increase when it is small. Birth rate can be density-dependent and death rate density-independent- leads to equilibrium population!
Population Dynamics
Density is not a static property but changes as individuals are added to or removed from a population. Additions occur through birth and immigration (the influx of new individuals from other areas). The factors that remove individuals from a population are death and emigration (movement of individuals out of a population and into other locations). Birth/death rates influence density of all populations, immigration/emigration alter density of many populations. Both (immigration/emigration) represent important biological changes among populations through time.
Disturbance Influences Species Diversity and Composition
Disturbance- event, like a storm/fire/flood/drought, that changes a community by removing organisms from it or altering resource availability. Nonequilibrium model-describes most communities as constantly changing after a disturbance. Relatively stable communities can be transformed (rapidly) into non equilibrium communities. Intermediate disturbance hypothesis- moderate levels of disturbance foster greater species diversity than do high or low levels of disturbance. High levels reduce diversity by creating environmental stresses that exceed tolerance of many species. Low levels can reduce diversity by allowing competitively dominant species to exclude less competitive ones.
Ecological Succession
Disturbed area colonized by a variety of species, which are gradually replaced by other species, and so on and so on. When this process begins in a virtually lifeless area where soil has not yet formed, such as on a new volcanic island or on the rubble left by a retreating glacier, it is called primary succession. In primary succession only life forms present initially are prokaryotes and protists. Lichens and mosses are usually the first macroscopic photosynthesizers to colonize such an area. Once soil develops grasses/shrubs/trees sprout from seeds blown in from nearby areas (or carried from animals).
Biotic Factors that Prevent Distribution
Do other species (biotic factors) limit distribution of a species. Inverse relationship between sea urchins and seaweeds. Where urchins that graze on seaweed are common, large strands of seaweeds do not become established. In addition to predation and herbivory, the presence or absence of pollinators, food resources, parasites, pathogens, and competing organisms can act as a biotic limitation on species distribution. Some biotic limitations are common in nature.
Species with a Large Impact
Dominant Species- species that are the most abundant or collectively have the highest biomass. Keystone species- not usually abundant in a community. Exert strong control on community structure by their pivotal ecological roles. Ecosystem engineers- species that dramatically alter environment. ie. beaver.
Types of Ecology
Ecosystem ecology (community of organisms in an area and the physical factors with which those organisms interact)- Emphasizes energy flow and chemical cycling between organisms and the environment. Landscape Ecology (mosaic of connected ecosystems)- focuses on factors controlling exchanges of energy, materials, and organisms across multiple ecosystems. Global Ecology (biosphere, global ecosystem sum of all planets ecosystems and landscapes)- examine how regional exchange of energy and materials influences the functioning distribution of organisms across the biosphere
Disturbance in Terrestrial Biomes
Ecotone- Area of intergradation of biomes (can be wide or narrow). Disturbance- Event such as a storm, fire, or human activity that changes a community, removing organisms from it and altering resource availability. ie- Frequent fires kill woody plants and keep a savanna from becoming the woodland that climate alone would support.
Energy, Water, and Species Richness
Evapotranspiration- evaporation of water from soil and plants. Function of solar radiation, temperature, and water availability is much higher in hot areas with abundant rainfall than in areas with low temperature or low precipitation. Species area curve- all other factors being equal, the larger the geographic area of a community, the more species it has. Large areas offer greater diversity of habitats and microhabitats. Species area curves for key taxa in a community helps ecologists predict how the loss of a given area of habitat will affect the community diversity.
Limits on Food Chain Length
Five or fewer links (generally) due to energetic hypothesis which suggests that length of a food chain is limited by the inefficient of energy transferred along the chain. On average, only about 10% of energy stored in the organic matter of each trophic level is converted to organic matter at the next trophic level. Thus, a plant producer of 100kg material can support about 10kg of herbivore biomass and 1kg of carnivore biomass. Food chains should be relatively longer in habitats characterized by higher photosynthetic production. Carnivores larger at higher trophic levels, the size of a carnivore puts an upper limit on the size of food it can take into its mouth.
Exploitation
General term for any (+/-) interaction in which one species benefits by feeding on another species, which is harmed in the interaction (includes predation, herbivory, and parasitism). Predation (+/-)- Reason for many adaptations Aposematic: warning coloration Batesian Mimicry: harmless species mimics dangerous one Mullerian mimicry: two or more unpalatable species resemble one another (cuckoo bee/yellow jacket). Mechanical defense: porcupine quills Chemical defense: skunk Cryptic coloration: camouflage
Food Web
Group of food chains linked together to form a food web. Ecologists diagram trophic relationships of a community using arrows that link species according to who eats whom. A given species may weave into web at more than one trophic level. Nonexclusive consumers (ie. fox may eat berries as a primary consumer, or eat rabbits as a tertiary consumer). Species with similar trophic relationships can be grouped into broad functional groups.
Community Ecology
Group of populations of different species= community. Community interactions are classified by whether they help, harm, or have no effect on species involved. Interspecific interactions include competition, predation, herbivory, parasitism, mutualism, and commensalism.
Incorrect Logistic Growth Model
Growth (black dots) of population of water fleas in a small lab culture does not respond well to the growth logistic model (red curve). This population overshoots carrying capacity of its artificial environment before it settles down to an approximately stable population size.
Positive Interactions: Conclusion
Have significant influence on structure of ecological communities. Like positive interactions, competition, and exploitation (predation, herbivory, and parasitism) also can strongly affect the structure of ecological communities.
Water Cycle
Importance: Essential to all organisms, availability influences rate of ecosystem processes, particularly primary production and decomposition in terrestrial ecosystems. Oceans contain 97% of water, 2% bound in glaciers and ice caps, 1% in lakes, rivers, and groundwater (negligible amount in atmosphere). Main process driving the cycle is evaporation by solar energy, condensation of water vapor into clouds and precipitation. Transpiration by terrestrial plants also moves large volumes of water into atmosphere. Surface and groundwater flow can return to oceans completing water cycle.
Competition
Is a -/- interaction. Occurs when individuals of different species compete for a resource that limits the survival and reproduction of each species. (ie. weeds growing in a garden compete with garden plants for nutrients and water, lynx and foxes in northern forests of Alaska compete for snowshoe hares). Competition exclusion: Two species competing for same limited resource cannot coexist permanently in the same place. In the absence of disturbance, one species will use the resources more efficiently and reproduce more rapidly than the other. Even a slight reproductive advantage will lead to elimination of inferior competitor.
Climate
Long term prevailing weather conditions in a given area. Four physical factors- temperature, precipitation, sunlight, and wind- are key components of climate.
Island Equilibrium Model
Islands, due to isolation and limited size, provide excellent opportunities for studying the biogeographic factors that affect species diversity of communities. Includes actual islands, and fragments of habitat (lakes, mountain peaks..etc). Balance between immigration of new species and the extinction of species already there. Immigration decreases as number of species increases (while the extinction rate increases). Greater likelihood of competitive exclusion. Size/distance from mainland also affect further immigration/extinction rates. Small islands have fewer resources/higher extinction, colonizers less likely to reach small islands. Number of species increases with island size.
Partial Food Web
Isolation of a portion of a food web that interacts very little with the rest of the community.
K-selection/r-selection
K-selection: selection for traits that are advantageous at high densities. *operates in populations living at a density near carrying capacity, where competition between individuals is much stronger. r-selection: Selection for traits that maximize reproductive success in uncrowded environments (low densities). *Said to maximize r, the intrinsic rate of increase, and occurs in environments in which population densities are well below carrying capacity or individuals face little competition.
Energy and Nutrient Dynamics in an Ecosystem
Law of conservation of mass- matter cannot be created or destroyed (like energy). Primary producers= autotrophs, most are photosynthetic organisms. Primary (herbivores), secondary (carnivores that eat herbivores), tertiary consumers (carnivores that eat carnivores). Detritivores- heterotrophic decomposers. Some animals (ie. earthworms) but mostly fungi and prokaryotes.
Population Cycles
Lynx/Snowshoe Hare populations rise and fall in approximately 10 year cycles (instead of just the Lynx rising/falling in relation to its prey, the hare's population). Cycles may be caused by food shortage during winter. Hares eat terminal twigs of small shrubs (food supply to the hare might cycle every 10 years). Cycles may be due to predator-prey interactions. Many other predators (besides lynx) also eat the hares, and they may overexploit the prey. Overexploitation by predators proven (ecologists tracked individual hares with radio collars to determine why they died, 95% killed by predators, NOT starvation). Without predators the hares would not cycle. When ecologists set up electric fences to keep predators from hares there was no population decline phase of the cycle.
Top-Down Model
N <-- V <-- H <-- P Also called trophic cascade model. Removing top carnivores triggers increase at each level preceding it. Biomanipulation: top down model to improve water quality in lakes with a high abundance of algae. Attempts to prevent algal blooms by altering density of higher level consumers. In lakes with three trophic levels, removing fish should improve water quality by increasing zooplankton density, thereby decreasing algal populations.
Ecological Niche and Natural Selection
Niche- specific set of biotic and abiotic resources that an organism uses in its environment. Includes temperature range it tolerates, time of day when active, size/kinds of food it eats, habitat. Resource partitioning- differentiation of niches that enables similar species to coexist in a community (ie. seven species of lizard occupying one tree because they feed on different things).
Nitrogen Terrestrial Cycling
Nitrifying bacteria convert ammonium to nitrate Denitrifying bacteria convert nitrate to nitrogen gas.
Phosphorus Cycle
Organisms require phosphorus as a major constituent of nucleic acids, phospholipids, and ATP. Phosphate most important form, plants absorb and use in synthesis of organic compounds. Largest accumulations of phosphorus are in sedimentary rocks of marine origin. Also in soil, soil particles bind PO4^3- (phosphate), recycling of phosphorus localized in ecosystems. Weathering of rocks gradually adds phosphate to soil, some leaches into groundwater and surface water and may eventually reach the sea. Phosphate taken up by producers and incorporated into biological molecules may be eaten by consumers. Phosphate returned to soil or water by either decomposition of biomass or excretion by consumers. Only relatively small amounts of phosphorus move through the atmosphere (via dust and sea spray)
Ecological Succession: Secondary Succession
Occurs when an existing community has been cleared by a disturbance that leaves the soil intact. Following the disturbance the area may return to something like its original state.
Bodies of Water
Ocean currents influence climate along the coasts of continents by heating or cooling overlying air masses that pass across the land. Oceans and large lakes moderate climate of nearby land. When land is warmer than water (hot day) the air over the land rises, drawing a cool breeze of water across the land. Air over water cools slower than air over land, when land gets cool at night the water draws the cool air and replaces land with warmer air.
Terrestrial Biomes
One way to highlight importance of climate on the distribution of biomes is to construct a climograph, a plot of the annual mean temperature and precipitation in a particular region. Mean temperature and precipitation create terrestrial biomes.
Exploitation: Parasitism
Parasitism (+/-)- Parasite derives nourishment from host, which is harmed in the process. Endoparasites (feed on internal parts of host, ie. tapeworm) Ectoparasites (feed on external surface, ie. ticks/lice) Parasites can significantly affect survival, reproduction, and density of their host population (either directly or indirectly). Ticks weaken moose hosts by withdrawing blood and causing hair breakage/loss. Weakened moose has a great chance of dying from cold stress or predation.
Nitrogen Cycle
Part of amino acids, proteins, and nucleic acids (also limiting plant nutrient). Plants use ammonium NH4+ and Nitrate NO3-. Bacteria can use all as well as Nitrite (NO2-). Animals only use organic nitrogen. Main reservoir is the atmosphere, which is 80% free nitrogen gas. Major pathway for nitrogen to enter ecosystem is via nitrogen fixation. Conversion of N2 to forms that can be used to synthesize organic nitrogen compounds.
Trophic Efficiency
Percentage of production transferred from one level to the next. Must always be less than production efficiencies because they take into account not only the energy lost through respiration and contained in feces, but also the energy in organic material in a lower trophic level that is not consumed by the next level. Energy loss represented in an energy pyramid, in which net production of different levels are arranged in tiers. Primary producers convert one 1% of energy available to them to net primary production.
Zonation in Aquatic Biomes
Photic zone- sufficient light for photosynthesis Aphotic zone-little light penetrates Pelagic zone- Photic + Aphotic Abyssal zone- deep ocean Benthic zone- sand and organic/inorganic sediments. Made up of communities of organisms called benthos (ranges from shore all the way down to sand of abyssal zone). Major source of food for benthic species is detritus (rains down from productive surface waters of photic zone). Thermocline- layer of abrupt temperature change (warm upper layer of water separated from cold lower layer by thermoclines)
Population Dynamics: Stability and Fluctuation
Population fluctuations from year to year or place to place (population dynamics) are influenced by many factors that also affect other species. In populations isolated from immigration and emigration fluctuation can still occur due to harsh weather, can also grow quickly due to mild weather/food availability. Predator/prey relationships
The Working Ecosystem
Populations are Dynamic: 1.) Change in size through birth, deaths, immigration, and emigration. 2.) Species migrate for abundant food 3.) Birth and death rates influence density of all populations. Species Interact in Diverse Ways 4.) Predation 5.) Herbivory 6.) Mutualism 7.) Competition Organisms Transfer Energy and Matter in Ecosystems 8.) Primary producers convert energy in sunlight to chemical energy through photosynthesis. Growth is limited by abiotic factors (temp, nutrients, light) 9.) Food chains are short in tundra because primary production lower than other ecosystems 10.) When one organism eats another, energy transfers from one trophic level to next at 10% 11.) Detritivores recycle chemical elements back to primary producers 12.) Chemical elements such as carbon and nitrogen move in cycles between physical environment and organisms.
Density-Dependent Population Regulation
Principle of feedback regulation applies to population dynamics. Without some type of negative feedback between population density and the rates of birth and death, a population would never stop growing. At large population sizes, negative feedback is provided by density-dependent regulation, which halts population growth through mechanisms that reduce birth rates or increase death rates. Kelp Perch- mortality rose proportionally as its density increased. Without sufficient kelp to hide in, the perch was vulnerable to predation by another species. Predation and other mechanisms of density-dependent regulation=negative feedback. Increased densities cause population growth rates to decline by affecting reproduction.
Pathogens and Community Structure
Produce especially clear effects when they are introduce into new habitats. Zoonotic pathogens- transferred to humans from other animals (via direct contact or a vector). Vector- parasite (tick, lice, mosquito). Identifying community of hosts and vectors for a pathogen can help prevent illnesses like Lyme disease, which is spread by ticks. Pathogens also influenced greatly by changes in the environment.
Positive Interactions: Mutualism
Refers to a +/+ or a +/0 interaction in which at least one species benefits and neither is harmed. Mutualism (+/+)- Common in nature. In some mutualisms each species depends on the other for survival and reproduction. In other mutualisms both organisms can survive on their own. Each partner benefits and each partner experiences a cost, it transfers materials that could have been used to support its own growth and metabolism. For an interaction to be mutualism, benefits to each partner must exceed the costs (mycorrhizae, plant transfers carbs to fungus, an fungus transfers phosphorous to plant)
Ecology
Scientific study of the interactions between organisms and the environment. Organized into a hierarchy that ranges in scale from organisms to the entire planet. Organismal ecology (physiological, evolutionary, and behavior ecology)- how an organism's structure, physiology, and behavior meet the challenges posed by its environment. Population Ecology (Population is a group of individuals of the same species living in an area)- Analyzes factors that affect population size and how and why it changes through time. Community Ecology (community is a group of populations of different species in an area)- Examines how interactions between species, such as predation and competition, affect community structure and organization. .
Reproductive Rates
Simplest way to describe reproductive pattern of a population is to identify how reproductive output varies with the number of breeding females and their ages. Direct counts, mark-recapture method, and molecular methods used to determine reproductive rates. Use PCR to produce a genetic profile of each female, extract DNA from an eggshell of each turtle nest and match nests to females. This approach allows researchers to identify how many females were breeding (of 198) and how many offspring each female produced. Reproductive output is measured as average number of female offspring produced by females in a given age group. Age-specific reproductive rates vary considerably by species. High reproductive rate does not always equal rapid population growth.
Trophic Structure
Structure and dynamics of a community depend on feeding relationships between organisms (trophic structure of the community). Position an organisms occupies on the food chain is its trophic level.
Population Ecology
Study of populations in relation to their environment. Explores how biotic and abiotic factors influence the abundance, dispersion, and age structure of populations. Populations evolve as natural selection acts on heritable variations among individuals, changing the frequencies of alleles and traits over time. Evolution remains a central theme when viewing populations in the context of ecology. Population is a group of individuals of a single species living the the same general area (rely on same resources, interact and breed with one another).
Abiotic Factors
Temperature, water, oxygen, salinity, sunlight, soil may also limit a species distribution (abiotic factors vary substantially over space and time).
Character Displacement
Tendency for characteristics to diverge more in sympatric than allopatric populations of two species. Galapagos finches- beak depths in these species are similar in allopatric populations but have diverged considerably in sympatric populations.
Diversity of Life Histories
When reproduction begins, how often the organism reproduces, and how many offspring are produced during each reproductive episode. Semelparity- "big-bang production" Ie. Salmon produce thousands of eggs in one reproductive opportunity before it dies. Iteroparity- repeated reproduction. Female loggerhead turtle produces four clutches totaling approximately 300 eggs per year. Then waits 2-3 years before laying more eggs. Some species produce a single offspring (rhinos) while most insects and many plants produce many offspring. Such variation in offspring number has other consequences as well (one offspring provided for much better than many offspring).
