Unit 8: Ecology

The scientific study of the interations between organisms and the biotic and abiotic components of their environment

• Levels:
  Organismal Ecology

• Population Ecology

• Community Ecology

• Ecosystem Ecology

• Landscape Ecology

• Global Ecology

• The long-term prevailing weather conditions in an area

• Climate is the most significant influence on the distribution of organisms on land (bc it influences distribution of plants)

• The four major physical components of climate are temperature, precipitation, sunlight, and wind​

1. Latitude & Sunlight Intensity:

   • Sunlight is most intense near the equator (tropics) and less intense at higher latitudes.

   • Angle of sunlight impact varies with latitude, affecting heat and light distribution.

2. Global Air Circulation & Precipitation:

   • Warm, wet air rises at the equator and flows towards the poles, causing high precipitation in tropical regions.

   • Dry, descending air creates arid climates around 30º north and south latitudes.

   • Rising air at approximately 60º north and south latitudes leads to abundant precipitation.

   • Cold, dry air flows toward the poles, creating dry, cold climates.

3. Wind Patterns:

   • Earth's rotation speed causes deflection of winds, resulting in trade winds blowing east to west in the tropics and prevailing westerlies blowing west to east in temperate zones.

   • Wind patterns are influenced by global air circulation and latitude.

• Ocean currents influence the climate of nearby terrestrial environments by heating or cooling overlying air masses that pass over land​

• Large bodies of water moderate the climate of nearby land due to the high specific heat of water​

• Mountains influence air flow over land and affect climate in surrounding aras

• Warm, moist air cools as it rises up a mountain and releases moisture on the windward side

• Cool, dry air absorbs moisture as it descends on the leeward side, creating a “rain shadow” ​

• Terrestrial organisms, particularly forests, can alter climate at local and regional scales​

• The darker color of forests cause them to absorb more solar energy than deserts or grasslands ​

• The climate becomes hotter and drier in areas where humans have cut down large forests ​

• Where humans have restored large forests, the climate becomes cooler and wetter​

• A microclimate refers to very fine, localized patterns in climate

• Mant features of the environment influence surrounding areas by casting shade, altering evaporation from soil, or changing wind patterns

Environments are characterized by differences in abiotic factors. These are nonliving factors such as temperature, light, water, and nutrients

• Biotic, or living factors, are other organisms that are part of an individual’s environment.

• They also influence the distribution and abundance of life on Earth

• The burning of fossil fuels along with deforestation have increased the concentration of greenhouse gases in the atmosphere.

• This has led to climate change, which is a directional change to he global climatge lasting 3+ decades

• Biomes are major life zones characterized by vegetation type (terrestrial/land biomes) or physical environment (aquatic biomes)

• Terrestrial biomes grade into each other, without sharp boundaries

• These areas of intergradation are called ecotones, they may be wide or narrow

• They are diverse as animal species from both biomes may be present in an ecotone

• This includes events such as storms, fires, or human activity that change a community

• For example, frequent fires can kill woody plants and maintain the characteristic vegetation of a savanna​

• For example, hurricanes create openings in forest canopies that allow different species to grow​

• In many biomes, even dominant plants depend on periodic disturbance​

• Occurs in equatorial and subequatorial regions

• In tropical rainforests, rainfall is relatively constant, about 200-400 cm annualy

• In tropical dry forests, precipitation is seasonal, about 150-200 cm anually with a long dry season

• High temperature year round with low seasonal variation

• Intense competition with vertical layering

• highest terrestrial biome diversity

• Major impact = deforestation

• Occur in bands near 30 degrees north and south of the equator and in the interior of continents

• Low and highly variable precipitation

• Temp can exceed 50 Cand may fall bellow -30 C

• Plants may be adapted to C4 / CAM photosynthesis

• Plants have physical defense/ animals nocturnal

• biodiversity issue = urbanization + irrigated agriculture

• Occurs in equatorial and subequatorial regions

• Precipitation is seasonal (30 - 50 cm average per year)

• Warm year round, temp from 24-29 C, more seasonally variable than tropical forests

• Grass adapted to fire/drought + Large herbivores

• Induced fires can maintain savanna, (-) = cattle ranching + overhunting

• Occur in midlatitude coastal regions on several continents

• Highly seasonal precipitation, rainfall average 30-50 cm

• Hot summers are 35C and cool springs are10 C

• Dominated by shrubs, small trees, grasses, herbs, all fire-adapted

• Diversity of small mammals, birds, reptiles, and insects

• (-) = Agriculture and urbanization

• Found on many continents

• Highly seasonal precipitation with dry winters and wet summers

• 30-100 cm annual precipitation w/ common drought

• Cold winters hot summers

• Dominant plants are grass/forbs —> adapted to fire/droughts

• Mostly converted to agricultural land

• NCF, or taiga, spans northern North America and Eurasia, the largest terrestrial biome

• 30 - 70 cm annual precipitation / periodic drought common

• Coastal coniferous forests are temperate rainforests that may receive 300+ cm of rain

• Cold winters/ hot summers

• Evergreen, conifers, and pines are dominant vegetation

• Migratory birds + large mammals

• Occur in midlatitudes in the Northern Hemisphere

• Significant precipitation during all seasons

• Cold winter / hot summer

• Mature TBF has vertical layers + dom. the plant is deciduous trees

• These forests have been heavily settled by humans

• Cover expansive areas of the Arctic, alpine tundra exists on high mountaintops at all latitudes

• Low annual precipitation in the Arctic with high in the Alpine

• cold winter / less than average summer

• Herbaceous vegetation, and permafrost restricts plant growth

• Migratory birds + mammals

• (-) = oil/mineral extraction

• Diverse, dynamic, and cover most of the Earth

• Less latitudinal variation than terrestrial —> characterized by physics and chemical environment

• This could include saltwater concentration (chemical)

• Oceans have major impact on biosphere

• Evaporate water provides most of the rainfall

• Photosynthetic marine organisms provide most of the O₂ and consume large amounts of CO₂

• Aquatic biomes are split into different zones based on light penetration, temperature, and depth

• Ordering —>

• Photic —>aphotic —> pelagic —> abyssal —> benthic

• Thermoclines are temperature boundaries that split cold and warm water

• This can lead to habitat stratification, nutrient distribution, and varying oxygen levels in aquatic biomes

• Turnover is when these split waters combine

• Size can vary from small pond to massive lake

• Temperate lakes experience thermocline whereas tropical do not / Factors such as salinity, O_2, and nutrients vary

• Oligotrophic lakes —> nutrient poor, O₂ rich, low organic sediment

• Eutropic —> nutrient-rich, high sediment, depleted O₂

• Surface Zones: Littoral (shore) and Limnetic (further out)

• Dispersal is the movement of individuals or gametes away from their area of origin or centers of high population density

• Dispersal contributes to the global distribution of organisms

• A population can be defined as a group of individuals of a single species living in the same general area

• Populations are described by their boundaries and size

• Boundaries may be natural or arbitrarily defined

• Density is the number of individuals per unit area or volume

• It’s difficult to count all individuals in a population, sampling techniques can be used to estimate density and population size

• Methods include extrapolating density from a plot

• Use indicators such as nests or burrows

• The mark-recapture method

• Density is a dynamic property

• Dispersion is the pattern of spacing among individuals within the boundaries of the population

• Determines an estimate of population size

• Capture, tag, and release a random sample of individuals (s) in a population

• Marked individuals are given time to mix back into the population

• Capture a second sample of individuals (n), and note how many of them are marked (x) / (N) = population size

• Formula = N = sn/x

• The influx of new individuals from other areas, and births increase population size

• The movement of individuals out of a population, and deaths decrease population size

Clumped:

• individuals aggregate in patches

• they may aggregate in areas of high resource availability and favorable physical conditions

• Mating behavior, group predation, or defense against predators can also influence clumped dispersion

Uniform:

• A dispersion where individuals are evenly spaced

• Some plants may secrete chemicals that inhibit germination/growth of competing individuals

• Animals may exhibit territoriality

Random:

• An unpredictable spacing dispersion/position of individuals is independent of one another

• Occurs in the absence of strong attractions or repulsions among individuals or constant distribution of key physical/chemical factors

• Biotic and abiotic factors influence birth, death, and migration rates of populations

• Demography is the study of these vital statistics of a population and how they change over time

• A survivorship curve is a plot of the proportion or numbers in a cohort still alive at each age, showing the pattern of survivorship for a population

• Ex: straight line = constant death rate

• Type Ⅰ: Low death rates during early and middle life and a sharp increase in death rates later in life​ (found in larger mammals —> produce few offspring with good care)

• Type Ⅱ: Constant death rate over the lifespan​

  Found in some rodents, invertebrates, lizards, and annual plants

• Type Ⅲ: High death rates for the young; death rate steeply declines for survivors of early period die-off (high offspring little care)​

• Many species are intermediate to these curves or show more complex patterns​

• Populations of all species have the potential to expand greatly when resources are abundant​

• In nature, unlimited growth is unsustainable because resources are depleted as the population gets larger​

• Results in a J-curve

• normal for populations who enter new environments

• This also represents populations that rebounded from drastic reduction

• Realistic models of population growth incorporate carrying capacity (K), the maximum population size that a particular environment can sustain​

• Crowding and resource limitation will affect the per capita birth and death rates, causing the per capita rate of population growth (r) to drop

• Results in a S-curve

• _{When population increases, it will be limited by carrying capacity}

• An organism’s life history comprises the traits that affect its schedule of reproduction and survival

• Life history traits are evolutionary otucomes reflected in the development, physiology, and behavior of an organism

• Refers to the case where individuals undergo a “one-shot” pattern of big-bang reproduction ​

• Refers to the case where individuals undergo repeated reproductive events throughout their lifetime​

• K-selection refers to the selection of life history traits that are advantageous when density is high (near K), resources are low, and competition is strong

• ∙ K-selected Populations: Strategy is to produce few offspring with higher cost (energy); Tend to stay close  to carrying capacity; Ex. Mammals 

  
  

• r-selection refers to the selection of life history traits that maximize reproductive success when density is low and there is little competition for resources

• ∙ R-selected Populations: Boom and Bust organisms (opportunistic); Strategy is to produce lot of  offspring with no parental care; Ex. Insects 

  
  

• If a death rate increases or a birth rate decreases with increasing density, it is density dependent ​

• In addition to predation, several other mechanisms can cause density-dependent regulation:​

• Competition for resources​

• Disease​

• Intrinsic factors​

• Territoriality​

• Toxic wastes

• A birth rate or death rate that does not change with population density is density independent ​

• Density-Independent factors affect the population regardless of density

• Examples include:
  Weather and Climate Events

• Natural Disasters

• Abiotic Factors

• Natural Disturbances

• Pollution

• Habitat Loss and Fragmentation

• Seasonal Changes

• Natural Phenomena

• Populations dynamics focus on the complex interactiosn between biotic and abiotic factors that cause variation in population size

• Metapopulations are groups of local populations linked my immigration and emigration

• Local populations in a metapopulation occupy discrete patches of suitable habitat surrounded by unsuitable habitat

• One important factor affecting population growth is a country’s age structure​

• Age structure is the relative number of individuals of each age in a population​

• Age-structure diagrams (pyramids) can help predict a population’s growth trends​

• For example, the pyramid for Zambia is skewed toward young individuals who could sustain explosive population growth through their future reproduction​

• Carrying capacity refers to the maximum population size of a species that a given environment can sustain indefinitely, considering factors such as the availability of resources (such as food, water, and shelter), competition with other species, and predation pressure

• Any interaction that occurs betwene individuals of different species

• These interactions include competition, predation, herbivory, parasitism, mutualism, and commensalism

• Competition (–/–) occurs when individuals of different species use a resource that limits survival and reproduction of both individuals​

• For example, garden weeds compete with garden plants for soil nutrients and water​

• Species do not compete for resources that are not in short supply​

• Local elimination of the inferior (lesser) competitor, can result when two species use the same limited resources

• For example, when Paramecium aurelia and Paramecium caudatum compete for resources in culture, P. caudatum is driven to extinction​

• Both species survive when cultured alone​

• Based on this result, G.F. Gause concluded that two species competing for the same limiting resources cannot coexist permanently in the same place​

• An organism’s ecological niceh is the specific set of biotic and abiotic environmental resources it uses

• For example, the nicje of a torpical tree lizard includes the temperature range in tolerates, the size of branches it perches on, the time it is active, and the size and kind of insects it eats

• This concept can be used to restate the CEP

• Two species cannot coexist permanently in a community if their niches are identical​

• Ecologically similar species can coexist if one or more significant differences in their niches arise

• Resource partitioning is the differentiation of niches that enables similar species to coexist in a community

• The fundamental niche of a species refers to the complete range of environmental conditions and resources in which it could potentially survive and reproduce, uninhibited by other factors like competition or predation. It's essentially the theoretical habitat where a species could thrive without any limitations.

• The realized niche refers to the actual set of environmental conditions and resources in which a species exists and reproduces in nature. This is often smaller than the fundamental niche due to competition, predation, and other biotic interactions.

• The tendency for characteristics to diverge more in sympatric than in allopatric populations of two species is called character displacement​

• This divergence allows them to coexist more effectively by exploiting different niches within their shared habitat.

• Exploitation refers to any +/– interaction in which individuals of one species benefit by feeding on individuals of the other species (which are harmed)​

• Exploitative interactions include predation, herbivory, and parasitism​

• Mechanical Defense (porcupine)

• Chemical Defense (skunk)

• Animals with chemical defenses often exhibit bright warning coloration, called aposematic coloration​

• Cryptic coloration, or camouflage, makes prey difficult to see in their environment​

• Some prey species are protected by their resemblance to other species​
  In Batesian mimicry, a palatable or harmless species mimics an unpalatable or harmful model​

• Harmless individuals that resemble members of a harmful species are avoided by predators that have learned not to eat the harmful ones​

• In Müllerian mimicry, two or more unpalatable species resemble each other​

• Predators can learn to avoid unpalatable prey faster when they encounter more of them with a similar appearance​

• The species diversity of a community, which is the variety of organisms it includes, has two components:

• Species Richness: the number of different species in a community

• Relative Abundance: The proportion each species represents of all individuals in the community

• Two communities can have the same species richness but a different relative abundance​

• The feeding relationships between organisms in a community, this is a key factor affecting community structure and dynamics

• Energy is transferred from autotrophs (primary producers) through herbivores (primary consumers) to carnivores (secondary and higher consumers)​

• Decomposers are the final link in this chain, which is referred to as a food chain​

• The position an organism occupies in a food chain is called its trophic level​

• A group of complex food chains linked together forming complex trophic interactions

• Arrows link species in the food web according to who eats whom

• The energetic hypothesis suggests that length is limited by inefficient energy transfer

• Only about 10% of the energy stored in organic matter at each tropic level is converted to organic matter at the next trophic level

• have strong effects due to their large size or high abundance​

• They often have community-wide effects because they provide habitat or food​

• They may be competitively dominant—superior in exploiting key resources such as space, water, nutrients, or light​

• Certain species have a large impact on community structure due to their abundance or pivotal role in community dynamics​

• Keystone species exert strong control on a community by their pivotal ecological roles​

• In contrast to foundation species, they are not usually abundant in a community​

• Organisms are controlled by what they eat (“bottom-up” control)​

• In bottom-up control, the abundance of organisms at each trophic level is limited by nutrient supply or food availability at lower levels​

• In this case, the biomass or abundance of organisms at lower trophic levels would have to be altered to change the community structure​

• Organisms can be controlled by what eats them (“top-down” control)​

• In top-down control, the abundance of organisms at each trophic level is controlled by the abundance of consumers at higher trophic levels​

• The effects of removing top level carnivores move down the trophic structure as alternating +/– effects​

• Disturbance keeps many communities from reaching equilibrium​

• A disturbance is an event that changes a community by removing organisms from it or altering resource availability​

• The nonequilibrium model describes communities as constantly changing after disturbance​

• The intermediate disturbance hypothesis states that moderate levels of disturbance foster greater diversity than do high or low levels of disturbance​

• High levels of disturbance exclude many slow-growing species​

• Low levels of disturbance allow competitively dominant species to exclude less competitive ones​

• Ecological succession refers to the pattern of colonization and species replacement that occurs in a community following a severe disturbance​

• When ecological succession begins in a virtually lifeless area, such as a new volcanic island, it is called primary succession

• During primary succession, prokaryotes and protists are the only life forms initially present​​

• Lichens and mosses arrive first, the soil gradually develops as rocks weather, and organic matter accumulates as early colonizers decompose ​

• The plant community is established after soil develops​

• Secondary succession involves the recolonization of an area after a major disturbance has removed most but not all of the organisms​

• For example, abandoned agricultural land may return to its original state through secondary succession

• Pathogens—disease-causing microorganisms, viruses, viroids, and prions—have strong effects on ecological communities​

• Pathogens can be particularly virulent new habitats because new host populations lack resistance​

• For example, white-band disease has decimated coral populations in the Caribbean, removing key habitat for lobsters, snappers, and other fish​

• For example, a protist causing sudden oak death has killed millions of oak trees, indirectly resulting in decreased abundance of at least five bird species​

• An ecosystem includes all the living organisms in an area and the abiotic factors with which they interact ​

• An ecosystem can encompass a large area, such as a forest, lake, or island, or a microcosm, such as the space under a fallen log or a small desert spring​

• Primary producers are autotrophs that build organic molecules using either sunlight or inorganic compounds as energy sources ​

• Most are photosynthetic plants, algae, and prokaryotes, but some are chemosynthetic prokaryotes​

• Herbivores are primary consumers; they eat primary producers ​

• Carnivores that eat herbivores are secondary consumers ​

• Carnivores that eat other carnivores are tertiary consumers​

• Decomposers are heterotrophs that get their energy from detritus, nonliving organic matter​

• In most ecosystems, primary production is the amount of light energy converted to chemical energy by autotrophs during a given time period​

• In some ecosystems, chemoautotrophs are the primary producers​

• The extent of photosynthetic production sets the “spending limit” for an ecosystem’s energy budget​

• Total primary production is known as the ecosystem’s gross primary production (GPP)​

• GPP is measured as the conversion of energy from light (or chemicals) to the chemical energy of organic molecules per unit time​

• Net primary production (NPP) is GPP minus energy used by autotrophs for respiration (R_a)​

NPP = GPP – R_a

• NPP averages about one-half GPP, and is expressed as​

• Energy per unit area per unit time [J/(m2 · yr)], or​

• Biomass added per unit area per unit time [g/(m2 · yr)]​

• In other words, NPP represents the net amount of organic material that is available as food for the rest of the ecosystem, after accounting for the energy invested by primary producers in their own growth and maintenance.

• Net ecosystem production (NEP) is a measure of the total biomass accumulation of producers and consumers during a given period​

• If NEP > 0, then an ecosystem stores carbon and acts as a carbon sink​

• If NEP < 0, then the ecosystem releases CO2 and becomes a carbon source​

• A limiting nutrient is the element that must be added for production to increase ​

• Nitrogen and phosphorous are the nutrients that most often limit marine production​

• Eutrophication is the process where primary production increases as an ecosystem changes from nutrient-poor to nutrient-rich​

• Excess nitrogen runoff fertilizes phytoplankton, causing algal blooms and the occurrence of fatally low oxygen concentrations in marine “dead zones”​

• Secondary production of an ecosystem is the amount of chemical energy in food converted to new biomass during a given period of time​

• Only energy stored as biomass in herbivores is available to secondary consumers​

• Water moves by the processes of evaporation, transpiration, condensation, precipitation, and movement through surface and groundwater ​

• Carbon reservoirs include fossil fuels, soils and sediments, dissolved compounds in oceans, living biomass, the atmosphere, and sedimentary rocks​

• Nitrogen, a component of amino acids, proteins, and nucleic acids, is often a limiting plant nutrient​

• The atmosphere is the main nitrogen (N2) reservoir ​

• N2 must be converted to NH4+ or NO3– for uptake by plants, via nitrogen fixation by bacteria​

• Some bacteria can also use NO2–​

• Animals can only use organic nitrogen compounds​

• Organic nitrogen is decomposed to NH4+ by ammonification,

• and NH4+ is decomposed to NO3– by nitrification​

• Phosphorus is a major constituent of nucleic acids, phospholipids, and ATP​

• Phosphate (PO43–) is the inorganic form of phosphorus used by plants​

• Reservoirs include marine sedimentary rocks, soil, the oceans (dissolved compounds), and organisms​

• Weathering of rocks releases phosphate into the soil, and it reaches aquatic systems through leaching​

• Bioremediation is the use of organisms—mainly prokaryotes, fungi, or plants—to detoxify polluted ecosystems​

• The organisms can take up and may metabolize toxic molecules​

• For example, the bacterium Shewanella oneidensis metabolizes uranium to an insoluble form, less likely to leach into streams and groundwater​

• Biological augmentation uses organisms to add essential materials to a degraded ecosystem​

• nitrogen-fixing plants can increase the available nitrogen in soil​

• adding mycorrhizal fungi can help plants to access nutrients from soil​

• Human activities alter natural disturbance, trophic structure, energy flow, and chemical cycling ​

• Conservation biology integrates ecology, physiology, molecular biology, evolutionary biology, and genetics in effort to conserve biological diversity​

• Genetic diversity comprises genetic variation within a population and between populations​

• The extinction of a population reduces the genetic diversity required for microevolution within a species​

• Species diversity is the number of species in an ecosystem or across the biosphere​

• Endangered and threatened species are of particular concern​

• An endangered species is in danger of extinction throughout all or much of its range​

• A threatened species is considered likely to become endangered in the foreseeable future​

• Human activity is reducing ecosystem diversity, the variety of ecosystems in the biosphere​

• For example, more than half of the wetlands in the contiguous United States have been drained and converted to other ecosystems

• Human alteration of habitat through agriculture, forestry, urban development, mining, and pollution is the greatest threat to biodiversity

• Habitat loss is implicated as the contributing cause for 73% of species that have become extinct, endangered, vulnerable, or rare in the last few hundred years​

• Introduced species are those that humans move from native locations to new geographic regions, either intentionally or by accident​

• Free from native predators, herbivores, pathogens or competitors, introduced species may spread rapidly​

• Introduced species that establish may prey upon or outcompete native organisms ​

• For example, the arrival of the predatory brown tree snake on the island of Guam was followed by extinctions of several bird and lizard species

• Overharvesting is harvesting of organisms at rates exceeding the ability of their populations to rebound​

• Species with restricted habitats, such as islands, are especially vulnerable to overharvesting ​

• Overfishing has decimated many commercially important wild fish populations​

• Global change includes alterations in climate, atmospheric chemistry, and broad ecological systems that reduce Earth’s capacity to support life​

• Acid precipitation is rain, snow, or fog that contains sulfuric or nitric acids causing a pH < 5.2​

• Acids form in the atmosphere with the release of sulfur and nitrogen from burning wood and fossil fuel​

• Air pollution from one region can result in acid precipitation downwind​

• Definition: Process leading to small population size to eventual extinction

• Causes: Inbreeding, genetic drift, demographic stochasticity

• Consequences: Reduced genetic diversity, increased risk of extinction

• Prevention: Habitat conservation, genetic rescue programs

• Minimum viable population (MVP) is the minimum population size at which a species can sustain its numbers​

• MVP is estimated by integrating many factors, such as an estimate of how many individuals are likely to be killed by storms or other catastrophes​