Exam 3 Ecology

ecosystem ecology

how energy and elements flow, considering both biotic and abiotic factors

trophic pyramid

• autotrophs- primary producers—capture ambient energy. they are at the bottom of the energy pyramid

• primary consumers- eat autotrophs, 2nd from bottom

• secondary consumers- 3rd from bottom

• tertiary consumers- top

• more energy available at the base of the pyramid

  • a lot of this energy is lost to physiological maintenance and activity (5-20% survives each level)

  • animals are less metabolically efficient than palnts so a lot of energy may be lost to movement or high metabolic rates

• Decomposers and scavengers use energy NOT consumed by higher trophic levels

• Parasites- use energy of host, not conventionally considered at higher trophic levels

• animals can eat at multiple trophic levels

predators at higher trophic levels

• require high productivity habitats

• forage over huge areas

• are less abundant than species at lower trophic levels

assimilation efficiency

• ratio of assimilation (energy gained) to ingestion (total energy in food)

• prey is higher than plants/seeds

net production efficiency

• ratio of energy contained in production (growth and offspring) to total assimilated energy

• Higher net production efficiency means higher biomass production

  • ectotherms have larger efficiency

• higher metabolic rates = lower effiiciency

• lower temperature = greater efificiency, higher = lower (so temperate plants have higher efficiency compared to tropical)

Deritus

• dead biomass

• going up the trophic pyramid, decomposition of deritus returns energy and nutrients back into a form usable by primary producers

• is really hard to digest, so it slows energy movement

allochthonous input

energy/nutrients that is produced outside an ecosystem and is transported in

• very useful in low-productivity environments

plants deposit carbon underground by

1. dying → their roots die and remain in soil

2. Plants’ carbon is taken by mutualists and parasites in the soil

recalcitrant carbon

organic carbon that resists breakdown, mostly found in soil but also some in ocean sediment

• is not involved in carbon cycle

labile carbon

organic carbon that is readily metabolized and moved along the carbon cycle

Sources of CO2

• CO2 can dissolve in ocean to become carbonic acid, lowering pH of sea water

• it can exist in minerals such as CaCO3 (calcite and limestone) and MgCO3 (dolomite) → releases out from these into environment

• Photosynthesis moves CO2 into the ground

• Respiration decomposition moves CO2 out via fires, harvesting/herbivory, and pathogen

photosynthesis

• converts light energy into chemical energy

• rubisco- enzyme linked to photosynthesis

• Plants control photosynth. by opening and closing their stromata (takes energy so it is a tradeoff)

  • by opening their stromata, they can absorb CO2 and emit O2 + H2O

• resources controls- CO2, water, light, nutrients

• Conditions controls- temperature

net carbon gain

• measures the energy sequestered from carbon in plant tissue

• used in place of NPP for an individual plant or area of ecological habitat

• units- mass/unit area*year

• varies with climate

carbon use efficiency

• fraction of photosynthesized C that goes into NPP

• decreases with stand age (age of the plant) and amount of non-photosynthetic tissue (less leaves = less photosynthesis)

ranking for net primary production in ecosystems (high to low)

1. wetland- not limited by water or temp

2. tropical wet forest, cultivated land

3. temperate forest

4. tropical dry forest

5. tropical woodland

6. boreal forest

7. temperate steppe

8. tundra

9. desert (limited by water and temperature)

NPP is controled by

• temperature -growing season length and nutrient supply

• precipitation- water supply

• vegetation type

• soil type- water and nutrient supply

decomposition

• physical and chemical breakdown of dead organic matter (litter and soil)

• mostly occurs through microbial respiration

• main decomposers-bacteria, archea, fungi, soil fauna

decompsition controls

• temperature

• moisture

• pH

• Soil biota

• Litter chemistry- defensive compounds, C:N ratio (rubsico), lignin (wood that breaks down slowly), traits to reduce water loss

• synergistic

permafrost

• soil that never thaws

• is where a lot of carbon is locked up

• as temperatures rise, it thaws and releases CH3 into the atmosphere, which causes climate warming (positive feedback system)

nitrogen cycle

• N2 is. 78% of atmosphere, is innert.

• N2 reaches soil or water through nitrogen fixation by microbes

• plants and algae absorb nitrogen as either NO3 or NH3

ammonification

breakdown of proteins, creating NH3 or NH4 as a product

• all organisms do some degree of ammonification, but soil fungi and microbes do a lot of it in nutrient cycling

nitrification

• the 2 separate reactions going from NH3 to NO2 and NO2 to NO3

• NH3 by nitrosomonas in soil, Nitrosococcus in ocean

• NO2 by nitrobacter in soil, Nitrosococcus in ocean

denitrification

• occurs under anaerobic conditions, where gaseous NO forms from NO3

• NO can then become N2

• NO and N2 denitrify soil or water because they are unusable nitrogen sources for primary producers

Immobilization

• take up of N by microbes, locking up N in organic forms inaccessible to plants

• soil microbes require both C and N, given the high C:N ratio

• Microbes may metabolize soil nitrogen and lock it into their own biomass

controls over litter decomposition

• high nitrogen:carbon means it will break down fast, low breaks down slow

• nitrogen cycles rapidly

• nitrogen can get stuck in leaf litter, less available for standing plants

Haber bosch process

• N2 + 3H2 = 2NH3

• used for fertilizer production

• largest source of reactive nitrogen (followed by biological N fixation and then fossil fuel burning)

terrestial ecosystems

• land based community of organisms and the interactions between biotic and abiotic components in a given area

• nutrient enrichment decreases plant diversity in these ecosystems

gulf of mexico

• Gulf is a semi-enclosed basin, acting as a sink for the draining terrestrial ecosystems across 31 states

• agricultural run off from terestrial ecosystems flow into the gulf, causing eutrophication (seasonal deadzone- no O2)

• sediment flow- rivers carry sediment from inland to coast

deadzones

• nitrogen saturation / biological deserts

• excess NO3 washes out of soil, pulling essential nutrients out of soil

• areas may be high in competitive exclusion, species loss, leading to silent zone

• denitrification cycle is imbalanced in these areas because of saturation of nitrogen

  • turns into nitrous oxide rather than N2

total nitrogen deposition

reactive nitrogen is related to high population density, intensive agriculture, and industrial activity

• causes loss of biodiversity

• soil acidification

• leaks into deadzones

to improve-

• Reduce input- make N use more efficient

• reduce transport of reactive N to rivers and ground water

• maximize denitrification to its N2 end product

richness

• number of species present

• when there is imperfect detection, you’d use species accumulation curves

evenness

• equity of relative abundances

• estimated through formulas

• high evenness- the species that are present have similar abundances

• low evenness- large skew in abundances of species

detection

• used to quanti

species accumulation curves

• show relationship between sampling intensity on x-axis and species/taxonomic richness on y-axis

• Sampling intensity increases = probability of finding more species initially increases but it levels off since the possibility of finding more species is rare

rarefraction

interpolates to standardize comparisons of species richness to a common number of individuals

• compares richness given diffeerent sampling intensities among communties

asymptotic estimators

extrapolate to estimate species richness given imperfect detection

• estimates richness of communities by extrapolating relationship between number of individuals collected

competition

• reduces biological diversity

• superior competitors can eliminate inferior

• intensity of competition depends on number of either competitor

• predation facilitates coexistence in guilds where competition alone causes inferior competitors to be eliminated

apparent competition

• effect whereby two noncompeting prey support the predator population

• either prey supporting predator population can indirectly increase predation on other species

apparent mutualism

effect whereby two noncompeting prey overwhelm the predator numerically

• possible when predator exhibits negative density dependence (predator interference)

Keystone predators

• predators that have a large impact on the ecological community (species richness, abundances) or ecosystem (energy, elemental flow)

keystone species

any species that has disproportionately large impact on a community or ecosystem relative to its own abundance

trophic cascade- “domino effect”

• indirect species interactions that originate with predators and spread downward through food webs

• doesn’t require prey consumption

• effect cascade- species on lower trophic that aren’t directly consumed are affected by organism, causing cascade at higher trophic level

• predators regulate ecological community

loss of top predator: shift in plant community composition

• loss of predator causes lower level population to grow high

• that population does selective grazing- avoids plants that are well defended

• well defended plants grow more abundant → affects ecosystem

loss of top predator- mesopredator release hypothesis

• mesopredator- intermediate predator

• top predator and mesopredator control population of shared prey

Green world hypothesis

• asks, if everything on earth is trying to eat and reproduce, why is the world still green?

• plants aren’t limited by herbivores-but light, water, nutrients.

• Herbivores are controled by predators → they can’t over-consume vegetation

• goes back to the idea of trophic cascades

odd vs even levels

• odd levels- each level is controlled by the next level. So, this allows more plants to grow, resisting environmental changes. This is more representative of the green world theory

• even levels- there is an intermediate player that is eaten so the herbivores aren’t being depleted enough to keep them from overgrazing. As a result, plants are more depleted.

bottom up effects

• opposite of trophic cascade

• occurs when there is an abundance of food → limits population size at and above the trophic level

• food abundance is tied to primary productivity → can cause spike in prey that is unrelated to primary productivity

top-down and bottom up effects visibility

• trophic cascades aren’t visible until researchers remove the predator or the predator goes extinct

• bottom-up effects aren’t observable until researchers experimentally increase primary productivity, primary productivity naturally increases in a burst, or if human activity incidentally increases primary productivity

redundancy

multiple species have similar characteristics in a community

• affects competition for non-food resources, intraguild predation, ability of prey to avoid predators, and abiotic stress

food chains

• show linear relationships linking primary producers to apex predators

• used to describe simple ecological communities

food webs

• describe complex relationships

• used to describe complex interactions with many species

• difficult to interpret

simpson index

• measure of richness and eveness

• probability that 2 randomly chosen individuals belong to different species

• D=1/ sum of p²

  • p is the proportion of ecological community made of i

  • when community is even D=species richness

alpha, beta, gamma diversity

• alpha diversity is within a sampling unit (ecological community)

  • local diversity, ie. a quadrat, a stream, island

  • evaluated by richness and evenness

• beta measures biodiversity turnover (between sampling units)

  • change across space or time

  • Bray Curtis distance/dissimilarity

• gamma is across all communities/samples (region)

  • evaluated by richness and evenness

Bray-Curtis Distance

• BC=1-(2Cij/Si+Sj)

• Cij- sum of lesser counts (lower abundance) of species shared by both communities

• Si- sum of abundances across all communities in i

• Sj— sum of abundances across all species in j

• higher means more dissimilar while lower means more similar

presence absencee B-diversity

• less informative without abundance

• turnover- difference in species found in neighboring areas

  • looks at who is there rather than how many of each species there is

• disproportionately driven by presence/absence of widespread species

dispersal

movement of individuals from one area to another

• between or within a population

• in fungi- passive transportation of spores, plants- seeds or spores, animals- transport in different life stages or active dispersion

• helps explain alpha and beta diversity

ways to study dispersal

• capture-mark-recapture- capture animal, mark it, release and try to find later

• scat of dispersers- collect poop, they know the range of the animal’s existence

• wind tunnel experiments- measures how far seeds are strewn as a result of wind turbulence

• radiotracking- following animals real time using a transmitter-direct path

• drones- real time tracking- direct path

dispersal kernel

• probability distribution that characterizes frequency of dispersal to different distances by an organism

• experimental or observed

dispersal limitation

• inability of species to reach all suitable habits in a defined area

• results in poor ability to move very far and/or low connectivity of habitat

dispersal impact on biodiversity

• sometimes negative effect on competitive ability

• worst competitors can become best dispersers by reaching evnironment that suits them, but then they can die out once species disperses

Janzen Connell Effects

• combine dispersal kernels with natural elements to understand the distribution of forest trees

• hypothesis- natural enemies prevent recruitment of offspring near their parents, facillitating coexistence among species

• gives rise to negative density-dependence, higher population size leads to greater aggregation to natural enemies and regulates tree species

• negative density-dependence allows for many competiting trees to coexist (creating higher biodiversity)

• observations- most seeds land directly under parent tree. Those are eaten, the seeds that land further are more likely to survive. Predators crowd around the tree → tradeoff

• hump is where the maximum recruitment happens → higher survival, far enough to hide from predators but close enough to have seeds

• effect prevents one species from taking over a patch of forest

Immediate disturbance hypothesis

• immediate frequencies of disturbance events will prevent competitively dominant species from eliminating competitively subordinate species

• assumes that populations of competitively dominant species grow slower than ruderal species

• assumes that ruderals are better dispers

• high disturbance means tha ruderals (sturdiest/fastest growing species) dominate (low diversity) while low means best competitors dominate (low diversity) → we want a happy medium

• local species diversity is maxed when ecological disturbance isn’t too rare or frequent

disturbance

an abrupt reduction in biomass due to some environmental change

• anything that rapidly kills

metapopulations

network of populations that undergo extinction and recolonization events in a spatial array of habitat patches

source habitats

• high quality patches of habitat

• large population size, unlikely to go extinct, individuals disperse to other patches and can recolonize empty patches/inc pop size

sink habitats

• low quality patches of habitat

• small population size

• b < d - high extinction risk without immigration from other patches

• long term persistence is only possible through rescue effects

landscape ecology

• types of habitats in a landscape

• areas of different habitat types

• spatial arrangement of habitat types

• how organisms use and move through dif. habitats

patch

area of fairly homogenous habitat that differs from surrounding area

• used to emphasize where organisms may spend most time or reproduce

corridor

area that facillitates dispersal, often connects different patches

matrix

large background area where patches and corridors are embedded

edge effects

• change in population or community structure at the boundary of two habitats

• some populations can’t really survive at the center of a habitat, so they live towards the edge, where things are milder

spatial autocorrelation

• closer things are more related than distant things

• makes it difficult to find out how things are related because basically everything is spatially related

metacommunities

set of communities linked by dispersal of their constituent species

• habitate differences among ecological communities

  • greater differences among habitat characteristics leads to greater beta diversity

  • greater variety of habitats increase gamma diversity by increasing range of species that can persist there

• higher dispersal of species causes

  • decreased beta diversity because species become more similar with more movement

  • increased alpha diversity- species reaches more communities, increasing local diversity

concept maps

• plot how ideas are related

• can show causality, similarities, or strength of relationships

types of maps

• range maps- characterize distribution of organisms

• outline map- encircle known range

• dot map- points where individuals have been found

species distribution modeling and ecological niche modeling

• establishes correlation between when species occurs and the environments in the locations

• helps estimate index of environmental suitability

• species distribution modeling focuses on the geography and realized niche, often used to estimate decrease in range size and shifts in ranges

• ecological niche modeling focuses on the niche and defines fundamental niche

• pros- easy to implement

• cons- uses circular logic and ignores biotic interactions

Buffon’s law

• distinct regions that are environmentally similar have distinct biological organisms

• challenges idea that environmentally similar but isolated regions have distinct assemblages of mammals and birds

ecological niche modeling

• tells you about biological needs of species

historical biogeography

• looks at how change in earth’s geography influences modern day distributions and patterns of biodiversity

• extended periods of isolation can facilitate distinct organisms

tectonic theory

• describes movement of tectonic plates of Earth’s crust in geographic space

• the connection of the land allowed the animals to move and distribute, which is why we see simialarities in land even though they are so far apart

Great American Interchange

• 3 million years ago

• mostly movement from north america to south via Panama canal. South American used to be island contient

• warmer and easier to thrive in south

pleistocene climate

• a lot colder

• drier in most of the world

• water locked up in ice - lower sea level

latiitudinal biodiversity gradient

• species richness usually declines going from the equator to the poles

  • exceptions- salamander, mariine taxa

• hypotheses for why- ecological, historical, etc.

Ahistorical hypothesis for LDG

• more energy towards the equator due to solar radiation near the equator, stimulates greater primary productivity, leading to greater plant diversity, longer food chains, and greater consumer diversity

• more intense competition is associated with narrow resource use (niche partitioning). Competition among many diverse species keeps competitor abundances low and avoid competitive exclusion

• greater kheystone predation

• epiphyte load- greater diversity of trees facilitates greater diversity of epiphytes

• greater diversity of hosts facilitates greater diversity of parasites

historical hypotheses for LDG

• higher speciation rates in tropical habitat (species have formed faster in tropical regions compared to poleward regions)

• Lower extinction rates in tropical habitats- they’re more stable environments, lower climate change near equator

• tropical habitat is more stable over both short and long time periods

  • short time period = low seasonality = greater specialization

  • long time period = tropical habitat remains same over long period = lower extinction rates and greater specialization

• tropical conservatism hypothesis vs out-of-the-tropics hypothesis

tropical conservatism hypothesis vs out-of-the-tropics hypothesis

• TCH- tropical habitats have been occupied longer for many groups of organisms, and dispersal and adaptation to nontropical envrionments is really rare because they are comfortable

  • Species will accumulate over time in tropical regions while no colonization occurs in temperate regions

• OTT- tropics are a cradle (high rates of speciatioin) and a museum (low rates of extinction)

  • species are always bubbling over-they originated in the tropics and then expanded towards the poles.

• Tropical cradle and museum can be competiting or non competing.

• tropical cradle

• tropics are a source of new species that then disperse and adapt to non-tropical regions.

• tropical museum

• tropical taxa have low extinction rate.