Ecology

community

a group of species that coexist and interact with one another within a defined area -Biologists may designate community boundaries based on natural boundaries (e.g., the edge of a pond) or arbitrarily; they may restrict study to certain groups (e.g., the bird community). -characterized by species composition: which species they contain and the relative abundances of those species

Biogeochemical Cycles Affect Global Climate: earths surface is warm

because of the atmosphere -All objects that are warmer than absolute zero emit electromagnetic radiation. -Most of the incoming solar radiation is in the visible range of wavelengths; some is absorbed in the atmosphere, some is reflected back to space, and some is absorbed by the Earth's surface.

interspecific interactions: mutualism

benefits both species: +/+ interaction -Leaf-cutter ants and the fungi they cultivate -Plants and pollinating or seed-dispersing animals -Humans and bifidobacteria in our guts -Corals and zooanthelae

interspecific interactions

between individuals of different species -affect population densities, species distributions, and lead to evolutionary changes. -can be beneficial or detrimental to either of the species -types: interspecific competition, consumer-resource interactions, mutualism, commensalism, amensalism

Climate and Topography Shape Earth's Physical Environments: global patterns of air circulation

driven by solar energy inputs, which are always greatest in the equatorial region -Hadley cells: tropical air is warmed, rises, and then cools (rising air releases lots of moisture/rainfall; replaced by surface air flowing in from north and south; cool and dry air sinks at 30°N and 30°S (most of deserts at these latitudes) -Coriolis effect: prevailing winds are deflected (change direction) by rotation of Earth

human activities alter ecological systems: move species

human-assisted biotic interchange: humans move species throughout the globe, sometimes deliberately, sometimes inadvertently. -Homogenizing the biota of the planet; blurring spatial heterogeneity in species composition that evolved during long periods of continental isolation

interspecific interactions: consumer resource interactions

organisms get their nutrition by eating other living organisms +/- interactions: the consumer benefits while the consumed organism loses -Includes predation, herbivory, and parasitism.

biome

a distinct physical environment inhabited by ecologically similar organisms with similar adaptations. -Species in the same biome in geographically separate regions display convergent evolution of morphological, physiological, or behavioral traits.

ecosystem

an ecological community plus the abiotic environment with which it exchanges energy and materials. -linked by processes and material movements -affected by climate and nutrients

species composition changes over space and time: climate change

can also cause temporal variation in communities. -As physical conditions change, the geographic ranges of species necessarily change with them

Climate and Topography Shape Earth's Physical Environments: variation in physical environment

results from atmosphere and ocean circulation patterns and geological processes. -Weather: the state of atmospheric conditions in a particular place at a particular time -Climate: average conditions and patterns of variation over longer periods -Earth receives uneven inputs of solar radiation due to spherical shape and tilt of axis as it orbits the sun

ecology

term coined by Ernst Haeckel in 1866 -made it a legitimate scientific subject -emphasized relevance to evolution: ecological interactions drive natural selection.

intraspecific interactions

within species interactions; reflected by density-dependent population growth -they are usually detrimental because per capita resource availability decreases as population density increases

still water biome (lake and ocean) zones

zones are related to water depth. 1) Nearshore regions (littoral or intertidal) are shallow, impacted by waves and fluctuating water levels; distinct zonation of species is common 2) Photic zone—depth to which light penetrates; photosynthetic organisms are restricted to this zone. 3) Aphotic zone is too deep for light penetration. 4) Benthic zone—lake or ocean bottom -water pressure increases with depth; deepest oceans = abyssal zone

Rapid Climate Change Affects Species and Communities: alter species distributions

-A rapid shift in plant community boundaries occurred after a drought in northern New Mexico: a ponderosa pine forest shrank abruptly and drought-adapted piñon-juniper woodland expanded by more than 2 km in less than 5 years, the new community persisted after the drought ended.

biological hierarchy

-biological hierarchy from the individual to the biosphere -Each level brings in new interacting parts at progressively larger spatial scales.

rarity advantage promotes species coexistence

-A species has a growth advantage when it is at a low density and its competitor is at a high density; this rarity advantage prevents the species from decreasing to zero. Result is coexistence. -Resource partitioning: different ways of using a resource; e.g.) separate tree into different nuts so different birds eat one type

critical biochemical cycles: humans affect global carbon cycle

-Any activity that impacts primary productivity can alter fluxes. -Runoff brings carbon to aquatic ecosystems. -Deforestation and fossil fuel burning increase atmospheric CO2. -Atmospheric CH4 is increased through livestock production, rice cultivation, and water storage in reservoirs (microbes in water-logged soils produce CH4).

Climate and Topography Shape Earth's Physical Environments: earth's topography influences climate

-As you go up a mountain, air temperature drops by about 1°C for each 220 m of elevation. -When prevailing winds bump into mountain ranges, the air rises up, cools, and releases moisture. -The now-dry air descends on the leeward side; results in a dry area on the leeward side, called a rain shadow

critical biochemical cycles: human activities affect the nitrogen cycle

-Burning fossil fuels, rice cultivation, and raising livestock releases oxides of nitrogen to the atmosphere; these oxides contribute to smog and acid rain. -Humans fix nitrogen by an industrial process to manufacture fertilizer and explosives.

Addressing ecological changes: present climate change is completely caused by humans

-But, science equips us to understand the natural world and devise solutions to problems. -Homo sapiens also has a remarkable capacity for cooperative action.

interspecific interactions can affect the distribution of species

-Competitive interactions can restrict the habitats in which species occur. -Two barnacle species compete for space on the rocky shorelines of the North Atlantic, with no overlap between zones occupied; a classic experiment removed each species and observed response of the other species.

small vs. large ecological system

-Large ecological systems tend to be more complex. -small systems can also be complex: human large intestine is densely populated with hundreds of microbial species; gut environment provides stable conditions and ample nutrients.

species composition changes over space and time: disturbance: secondary succession

-Components of an ecosystem can be changed by natural events, such as fires. -When the disturbance is over, community interactions tend to restore the ecosystem to its original condition through secondary succession. -Healthy ecosystems usually recover from natural disturbances, but may not recover from long-term, human-caused disturbances. -If the original community is not reestablished, there is an ecological transition to a different community

Ecological Investigation Depends on Natural History Knowledge and Modeling

-Computer models are important tools in the study of ecosystems. -Natural history knowledge is used to build these models. -Example: rangeland grasses are affected by other plants and herbivores, soil fertility, climate, and fire; to predict the effect of removing cattle to bring back grasses, all these interactions must be known

trophic interactions can change species composition of communities

-Consumer-resource interactions can have ripple effects across trophic levels, resulting in a trophic cascade. -In Yellowstone National Park, wolves were lost from the park due to hunting by 1926; elk were hunted by humans each year to prevent them from exceeding carrying capacity, until 1968. Elk population then rapidly increased. The elk browsed aspen trees so heavily that no young aspens couldn*t get a start; beavers (who depend on willows for food) were nearly exterminated, wolves were reintroduced in 1995 and preyed primarily on elk; aspen and willows grew again, and the beaver population increased.

species composition changes over space and time: disturbance

-Creates a steady turnover in species composition. 1) Species turnover can result from disturbance events: volcanic eruptions, wildfires, hurricanes, landslides, human activities -some or all the species are wiped out, and environmental conditions are changed. 2) Species often replace one another in a predictable sequence called succession; sometimes, an ecosystem changes in response to an abrupt disturbance; at other times, change occurs as a more gradual response to natural fluctuations in the environment

trophic interactions: niche

-Each species in a community has a unique niche. 1) the environmental tolerances of a species, which define where it can live. 2) ways a species obtains energy and materials 3) patterns of interaction with other species in the community.

fluxes of matter are driven by biogeochemical processes

-Earth is an open system with respect to energy, but a closed system with respect to matter. -The sun provides a steady input of energy. -There is a fixed amount of each element of matter, but biological, geological, and chemical processes can transform it and move it around the planet in biogeochemical cycles

communities change over space and time

-Ecologists have documented recurring patterns of species compositional change -It varies: 1) along environmental gradients 2) after disturbances 3) with changing climate.

species composition changes over space and time: along environment gradients

-Envirnomental gradients: such as elevation or soil types; e.g.) Zonation of organisms along a mountain side -transect: straight line used for ecological surveys; a transect along an environmental gradient will show the species turnover through space; allows you to sample a small, representative sample of the environment -Many animal species are associated with particular plant communities: food & habitat

ecology tools for managing populations: corridor

-For some species, a continuous corridor of habitat is needed to connect subpopulations and allow dispersal. -Dispersal corridors can be created by: 1) maintaining vegetation along roadsides, fence lines, or streams 2) building bridges or underpasses that allow individuals to avoid roads or other barriers. 3) Fish ladders

species richness: varies with latitude

-Geographic patterns of species richness suggest factors that affect diversity. -Greatest diversity of many plant and animal groups occurs in the tropics -island biogeography: theory that equilibrium species richness on islands depends on relative rates of colonization and extinction; small islands = small populations sizes, greater likelihood of extinctions. more isolated islands: less likely that colonizers will reach it

Addressing ecological changes: IPCC

-Governments have cooperated to support large-scale initiatives, such as the IPCC. -International agreements include: 1) Montreal Protocol to prevent depletion of UV-absorbing ozone 2) Kyoto Protocol to reduce emissions of greenhouse gases 3) Convention on International Trade in Endangered Species (CITES), to conserve species by eliminating international trade.

Biogeochemical Cycles Affect Global Climate: greenhouse gasses

-Greenhouse gases include H2O, CO2, CH4, N2O. -Without the atmosphere, Earth's average surface temperature would be about 34°C colder than at present. -Keeling's measurements from atop Mauna Loa in Hawaii show a steady increase in CO2 since 1960. -Analyses of air trapped in glacial ice demonstrate that CO2 and other greenhouse gases began increasing after about 1880. -Average annual global temperature has also increased.

human activities alter ecological systems: human-dominated ecosystem

-Human-dominated ecosystems (croplands, pasturelands, urban settlements) now cover about half of Earth's land area -these ecosystems have fewer interacting species and are less complex.

critical biochemical cycles: biogeochemical cycles are interconnected

-If carbon uptake by primary producers increases, uptake of P, N, and other elements also increases. -if decomposition rates increase, flux of elements back to inorganic compartments increases. -Any nutrient can limit biological function; the limiting one is the one that is in lowest supply relative to demand.

Rapid Climate Change Affects Species and Communities: alter community composition

-If populations cannot respond to changing environments, they may go extinct, resulting in changing species compositions. -Shifts in the geographic distributions can lead to assembly of novel communities. -Species have moved up mountains and towards higher latitudes. -Species shift at different rates or not at all, resulting in different species combinations.

critical biochemical cycles: biogeochemical cycles can interact in hard-to-predict ways

-Increased atmospheric CO2 can increase water- use efficiency by terrestrial plants -In a high CO2 environment, the plants have stomata open less, which reduces loss of water vapor

resources and physical conditions shape life histories

-Individual organisms require resources (materials and energy) and physical conditions they can tolerate. -Rate at which an organism can acquire resources increases with the availability of the resources.; Ex: photosynthetic rate increases with sunlight intensity, an animal's rate of food intake increases with the density of food.

critical biochemical cycles: global nitrogen cycle

-Involves chemical transformations. -N2 gas is 78% of the atmosphere, but most organisms cannot use this form; nitrogen fixation: some microbes can break the strong triple bond and reduce N2 to ammonium (NH4+). -Other microbial species convert ammonium into nitrate (NO3−) and other oxides of nitrogen; N-fixing reactions are reversed by yet another group of microbes in denitrification, which returns N2 gas to the atmosphere.

human population is unique

-It has grown at an ever-faster per capita rate, as indicated by steadily decreasing doubling times. -Technological advances have raised carrying capacity by increasing food production and improving health

ecology tools for managing populations

-Knowledge of life histories helps us to manage population -knowledge of metapopulation dynamics helps us to conserve species

Climate and Topography Shape Earth's Physical Environments: spatial arrangement of continents and oceans influence climate

-Major ocean surface currents; driven by prevailing winds -Deep ocean currents: driven by water density differences; colder, saltier water is more dense and sinks to form deep currents; deep currents regain the surface in areas of upwelling, completing a vertical ocean circulation -Oceans and large lakes: moderate climate because water has a high heat capacity. -Poleward-flowing ocean currents carry heat from tropics toward the poles, moderating climate at higher latitudes (Gulf Stream warms northern Europe)

introduced species alter interspecific interactions: invasive species spread by

-Marine species carried in ballast water on ships. -Terrestrial species carried unknowingly by humans as we move around globe; e.g.) seeds stuck in the mud on the bottom of shoes -Deliberate introductions (e.g., Europeans brought many plants and animals to their new homes). -Species are still being transported— ornamental plants, exotic pets, etc

critical biochemical cycles: global carbon cycle

-Movement of carbon is linked to energy flow through ecosystems; biomass is an important pool. -The largest pools occur in fossil fuels and carbonate rocks. -Photosynthesis moves inorganic carbon from the atmosphere and water into the organic compartment; respiration reverses this flux.

species diversity: affects community processes and outputs

-NPP is generally greater and more stable as species diversity increases. -A long-term study of prairie plant communities found that above-ground biomass increased as species diversity increased; the most species-rich plots also had the most plant functional groups: (plant groups differing in traits such as:ability to grow in warm versus cool seasons, associations with N-fixing bacteria, allocation to growth versus reproduction)

species composition changes over space and time: disturbance: primary succession

-On land, succession that occurs on surfaces where no soil exists (newly exposed surfaces such as volcanic rock and ash) -occurs on rock surfaces formed after volcanoes erupt; volcanic eruption destroys previous ecosystem - The first species to populate the area are called pioneer species; first organisms to appear are lichens; mosses soon appear, and grasses take root in the thin layer of soil; eventually tree seedlings and shrubs sprout

interspecific interactions with bad consequences

-Per capita growth rate of each species is modified by the presence of the other, positively or negatively. -Population densities are increased in positive interactions and decreased in negative interactions. -In interactions with negative effects, extinction of one or both species is possible

geography

-Physical geography: climates and surface features -Biogeography: distributions of organisms -Organisms must be adapted to their physical environments (eg. a plant that has no means of conserving water cannot thrive in a desert);species are found only in environments they can tolerate.

interspecific interactions can lead to extinction

-Populations show different dynamics in the presence or absence of other species. -Conclusions from the Paramecium studies, and from mathematical models: 1) Presence of a competitor always reduces population growth rate. 2) When two species coexist, they have lower equilibrium population densities than either would alone. 4) In some cases, competition causes one species to go extinct.

materials in bodies of living organsims are from abiotic resources

-Primary producers take up elements from inorganic pools and accumulate them as biomass. -Trophic interactions pass the elements on to heterotrophs. -Decomposers break down the dead and waste matter pool into elements that are available again for uptake by primary producers.

Rapid Climate Change Affects Species and Communities: can leave species behind

-Recent warming and other climate changes are far more rapid than anything organisms have experienced in their evolutionary histories; life cycles have evolved so that critical events occur at favorable times of year, climate change is altering the timing of environmental cues, rates of evolution may be too slow to keep up with an environment that changes too rapidly. 2) In the short term, many species seem to be adapting ; Ex. trees leaf out earlier in the spring; but some species may not respond to climate change or may not be able to continue adaptive tracking.

BIDE Model of population growth

-adds the number of immigrants (I) and emigrants (E) to the BD growth model

critical biochemical cycles: humans affect water cycle by changing land use

-Reduced vegetation (deforestation, cultivation, etc.) reduces precipitation retained in soil and increases amount that runs off. -Groundwater pumping depletes aquifers, brings water to surface where it evaporates. -Climate warming will melt ice caps and glaciers and cause sea level rise and increased evaporation; water vapor is a greenhouse gas.

Rapid Climate Change Affects Species and Communities: changes in seasonal timing disrupt interspecific interactions

-Some environmental cues do not change, such as day length, so temporal relationships among cues are shifting. -There may be timing mismatches among species in a community, which will disrupt interactions ; hatch of pollinators and opening of flowers

human activities alter ecological systems

-Some have suggested we are entering a new geological period, the "Anthropocene." -We are changing the distributions of organisms, vegetation, and topography, as well as Earth's climate.

mutualism

-Species benefit other species because acting in their own self-interest happens to benefit others. -Most pollinators visit flowers to get food and happen to pollinate the flowers in the process; flowers provide food (usually as little as possible) to lure the animals -cheating in mutualism: some flowers mimic the form and smell of female insects and are pollinated when males attempt to copulate with them, some bees bite holes in the base of flowers and eat the nectar without pollinating the flower

introduced species alter interspecific interactions

-Species introduced into a region where their natural enemies are absent may reach very high population densities. -They may become invasive—reproduce rapidly and spread widely, and have negative impacts on native species; usually take over and cause a decline/cause extinction in the native species

form and location of elements determine their accessibility to organisms

-The different forms and locations can be represented as compartments. -Pool: total amount of an element or molecule in a compartment. -Flux: movement of an element or molecule between compartments.

island biogeography suggest strategies for maintaining community diversity: large areas are being fragmented

-The fragments can be seen as habitat "islands" surrounded by "seas" of human-modified habitat. -The theory of island biogeography suggests ways to minimize effects of fragmentation. 1) Enhance colonization: -cluster habitat fragments together -connect fragments with dispersal corridors 2) Reduce extinctions: -retain large patches of original habitat -maintain ability of the fragments to support healthy populations.

consumer resource interactions

-The opposing interests of the consumer and the resource species can lead to an "evolutionary arms race," -prey continually evolve better defenses and predators continually evolve better offenses -Strategies of resource species (prey species): speed, size, or weapons, hide or use camouflage, mimic unpalatable species, sessile species have thick armor or are non-nutritive or poisonous. - Strategies of consumers: greater speed, size, or strength, keen senses, armor-piercing or crushing tools, means of detoxifying poisons -plants produce a variety of toxic chemicals against herbivores and pathogens

multiplicative growth has a constant doubling time

-The time it takes a population to double in size can be calculated if r is known. -r decreases as the population becomes more crowded because birth rates decrease and death rates increase; because r is density dependent -When r = 0, the population size stops changing; it reaches an equilibrium size K (carrying capacity)

critical biochemical cycles: nitrogen & eutrophication

-Topsoil and dissolved nitrates are lost from farm fields and deforested areas by wind and water runoff. -The nitrates are deposited in aquatic ecosystems and result in eutrophication— increased primary productivity and rapid phytoplankton growth. -Decomposition of the phytoplankton can deplete oxygen; other organisms can not survive, and dead zones form offshore in summer.

critical biochemical cycles: global water (hydrological) cycle

-Water is essential for life; makes up 70% of living biomass -Flowing water is an erosion agent and transports sediment; moves material around the planet. -Solar-powered evaporation moves water from ocean and land surfaces into the atmosphere; the energy is released again as heat when water vapor condenses.

intraspecific competition

-density-dependent growth models assume all individuals in a population are equally affected by density. -But individuals vary, and some traits may increase the ability to obtain resources. -Natural selection will favor the trait and its frequency will increase in the population (directional selection). ; more resources will be available for this phenotype, increasing the carrying capacity.

ecological communities provide humans with critical goods and services

-depend on community diversity. -Ecosystem services include: food, clean water, clean air, fiber, building materials, fuel, flood control, soil stabilization, pollination, and climate regulation. -have economic value -humans are rapidly converting natural communities into less diverse, human-managed communities; croplands, pastures, and urban areas.

trophic interactions nergy is lost as it moves through food web

-food web: arrow indicates flow of energy & materials -Net primary productivity (NPP)— change in biomass of primary producers (dry mass) per unit of time is an approximation for NPP. -Ecological efficiency is about 10%: limits number of trophic levels in a community; so low because not all the biomass at one trophic level is ingested by the next one: some parts of the meal are left behind, some ingested matter is indigestible and is excreted as waste (hair, teeth), and organisms use much of the energy to fuel their own metabolism

human population is unique: Malthus

-he pointed out that the human population was growing multiplicatively, but its food supply was growing additively, and predicted that food shortages would limit human population growth. -he could not predict the effects of technology such as medical advances and the Green Revolution

ecological systems can be unique

-in the human gut, the microbial species vary from person to person and with diet. -the host's genotype and diet affect the gut environment from the bacterial point of view; and the bacteria influence their environment, which includes the host. every desert is not just like another

human activities alter ecological systems: agricultural lands

-monocultures replace species-rich natural communities -diversity of crops planted is very low: 19 crops comprise 95% of total global food production -agricultural systems are more spatially and physically uniform than natural ecological systems

diversity

-represents a balance between colonization and extinction -oceanic islands have fewer species than areas of comparable size on nearby mainlands -Small islands contain fewer species than large islands, and isolated islands contain fewer species than comparable-size islands closer to a mainland.

human population is unique: overshot carrying capacity

-why: 1) Technological advances and agriculture have depended on fossil fuels, a finite resource. 2) Climate change and ecosystem degradation have been a consequence of 20th century population expansion. -If the human population has indeed exceeded carrying capacity, ultimately it will decrease; we can bring this about voluntarily if we continue to reduce per capita birth rate

Biogeochemical Cycles Affect Global Climate: human activities are contributing to changes in earths radiation balance

1) Adding greenhouse gases to the atmosphere 2) Deposition of dust and dark-colored soot particles ("black carbon") from fossil fuel burning increases amount of solar energy absorbed by snow and ice; increases melting. 3) Adding aerosols to the atmosphere increases reflectance of solar energy, less reaches Earth's surface -when all human effects are added to climate models, climate scientists conclude human activities have contributed significantly to recent climate warming.

human activities alter ecological systems: reduce complexity in natural ecosystems

1) Damming and channelization of rivers 2) Pollution and habitat fragmentation 3) Overexploitation of wild species 4) Introductions of new species

population abundance varies on several scales

1) Geographic range: region in which a species is found 2) Within the range, species may be restricted to specific environments or habitats. 3) Habitat patches are "islands" of suitable habitat separated by areas of unsuitable habitat -Population densities are dynamic —they change over time; density of one species population may be related to density of other species populations.

Biogeochemical Cycles Affect Global Climate: higher global temperature are affecting climate

1) Hotter air temperatures 2) A more intense water cycle, with greater overall evaporation and precipitation. 3) Hadley cells are expected to expand poleward; warmer tropical air will rise higher and expand farther toward the poles before sinking. 4) Precipitation will increase near the equator and at high latitudes and decrease at mid-latitudes.

interspecific interactions that modify per capita growth rate

1) Interspecific competition: effect of the other species would be subtracted in the growth model. 2) Consumer-resource interactions: effect of the consumer is subtracted in the equation for the resource species; the effect of the resource is added in the equation for the consumer, since the consumer benefits.

population measures of abundance

1) Population density: number of individuals per unit of area or volume 2) Population size: total number of individuals in a population -Counting all individuals is usually not feasible; extrapolation

NPP

1) a measure of ecosystem function -Most: tropical forest, temperate forest, swamp and marsh; least in desert & open ocean -Temperature increases, NPP increases 2) NPP varies predictably with climate and nutrients -Aquatic NPP is strongly affected by nutrient availability and light penetration; nutrients are most abundant in near-shore areas and upwellings, hydrothermal vents are productive areas in the deep oceans, where chemotrophs use chemical energy rather than sunlight

trophic interactions

aka Consumer-resource interactions; cause energy and materials to flow through a community. -Trophic levels: feeding positions 1) Primary producers (autotrophs) convert solar energy into form usable by the rest of community 2) Heterotrophs get energy by breaking apart organic compounds that were assembled by other organisms; primary consumers (herbivores) eat primary producers, secondary consumers (carnivores) eat herbivores, tertiary consumers eat secondary consumers -Omnivores feed from multiple trophic levels

population growth is multiplicative

an ever-larger number of individuals is added in each successive time period. -In additive growth, a constant number (rather than a constant multiple) is added in each time period. -This ecological struggle for existence, fueled by multiplicative growth, drives natural selection and adaptation.

critical biochemical cycles: excess nitrogen

can change plant species composition. -Species adapted to low nutrient levels grow slowly, even when fertilized, and can be easily displaced by faster-growing species that take advantage of additional nutrients. -In the Netherlands, this has caused 13% of the recent loss of plant species diversity.

births increase and deaths decrease population size

change in population size depends on the number of births and deaths over a given time. -"Birth-death" or BD model of population change: 1) Per capita birth rate (b): number of offspring an average individual produces 3) Per capita death rate (d): average individual's chance of dying 3) Per capita growth rate (r) = (b - d) = average individual's contribution to total population growth rate

aquatic biome

determined by physical factors such as water depth and current, temperature, pressure, salinity, and substrate characteristics -In streams, current velocity is important; organisms must have adaptations to withstand flow -Current also impacts the substrate; whether rocky, sandy, silty, substrate also determines what species are present

restoration ecology

focuses on restoring function to degraded ecosystems. -One goal is to restore original species diversity -Disturbance sometimes results in an ecological transition to a very different community; may be very difficult to reverse transition and restore original community.

principle of allocation

once an organism has acquired a unit of some resource, it can be used for only one function at a time: maintenance, foraging, growth, defense, or reproduction. -In stressful conditions, more resources go to maintaining homeostasis. -Once an organism has more resources than it needs for maintenance, it can allocate the excess to other functions.

ecological system

one or more organisms plus the external environment with which they interact -Abiotic components: nonliving -Biotic components: living organism

interspecific interactions: commensalism

one species benefits while the other is unaffected (+/0 interaction). -Cattle convert plants into dung, which dung beetles can use.

interspecific interactions: amensalism

one species is harmed while the other is unaffected (-/0 interactions). -Tend to be more accidental than other relationships. -Example: a herd of elephants that crush plants and insects while moving through a forest.

species interactions can affect individual fitness

phenotypes that gain the most from a positive interaction or suffer least from a negative interaction will increase in frequency in the population, and the population will evolve

Addressing ecological changes: climate has changed in the past

precipitated five major mass extinctions. -There is precedent for atmospheric changes induced by organisms: 1) the first photosynthetic microbes increased oxygen concentrations to a level that was toxic to the anaerobic prokaryotes. 2) The first land plants caused another rise in oxygen concentrations 250 million years ago.

Biogeochemical Cycles Affect Global Climate: greenhouse effect

recent increases in greenhouse gases are warming Earth's surface -Earth's surface re-emits energy in longer, less energetic infrared wavelengths. -Some of this infrared radiation is absorbed by gas molecules in the atmosphere (greenhouse gases). -The molecules are warmed and radiate photons back to Earth's surface, keeping the energy within the Earth system as heat.

interspecific interactions: interspecific competition

refers to -/- interactions -Members of two or more species use the same resource. -At any one time there is often one limiting resource in the shortest supply relative to demand.

species distribution

reflect the effects of environment on per capita growth rates -as average individuals in a population acquire more resources, the average fecundity, survivorship, and per capita growth rate increase. -Life-history tradeoffs: negative relationships among growth, reproduction, and survival (eg. investments in reproduction may be at the expense of adult survivorship or growth); environment is also a factor: if high mortality rates are likely, it makes sense to invest in early reproduction

life table

shows ages at which individuals make life cycle transitions and how many individuals do so successfully. -Life tables have two types of information: 1) survivorship: fraction of individuals that survive from birth to different life stages or ages 2) fecundity: average number of offspring each individual produces at those life stages or ages

Biogeochemical Cycles Affect Global Climate: warming is spatially uneven

so precipitation changes will be season- and region-specific. -In general, wet regions are expected to get wetter and dry regions drier. -Precipitation trends in the twentieth century support these expectations. -Warming may also increase storm intensity.; strong hurricanes (category 4 and 5) have become more frequent since the 1970s.

critical biochemical cycles: dissolved Co2 in oceans

some is converted by primary producers, and enters the trophic system. -Organic detritus and carbonates continually drift down to the ocean floor. -Some organic detritus in ocean sediments is converted to fossil fuels; carbonates can be transformed into limestone.

life history

time course of growth and development, reproduction, and death during an average individual's life -quantitative descriptions of life cycles -Can vary among species: how many and what types of developmental stages, age of first reproduction, frequency of reproduction, how many offspring they produce, how long they live -Life histories can vary within a species; different human populations have different life expectancies and age of sexual maturity

species diversity

two components: 1) Species richness: number of species in the community 2) Species evenness: distribution of species' abundances -Both aspects of diversity affect community function. -A species' influence in a community depends on its interactions & its abundance. -Communities with a few very abundant species are largely defined by them, rather than by the many rare ones.