Ecology Exam 3
Biogeography
Biogeography is the study of the variation in species composition and diversity among geographic locations
Alpha diversity is biodiversity at a local scale, and is driven by physical conditions and species interactions
Gamma diversity is biodiversity at a regional scale, and is driven by differences in rates of speciation, extinction, and dispersal across the landscape
Beta diversity is biodiversity that occurs due to differences between local and regional diversity, and is driven by species turnover
Gamma/alpha
Theory of island biogeography
Larger areas can hold more species and have a lower rate of extinction
Islands closer to the mainland have a greater probability of colonization
S=cA^z
Has a saturating curve, so it is graphed on a log scale (log S = log C + z log A)
Biodiversity increases with area
One large area has more biodiversity than multiple small areas that have the same area added together
Islands are more vulnerable to extinctions
Interactive, assortive, evolutionary
Global patterns of biodiversity are the result of variations in speciation, extinction, and dispersal at latitudinal and continental spatial scales and evolutionary time scales
Alfred Russel Wallace mapped out major zoogeographic regions of the Earth where there are distinct
Wallace noticed that the birds and mammals of Bali and Lombok were strikingly different
The fauna evolved on two different continents that only came into proximity in the last 15 million years
When sea levels were lower, deep water kept Asia and Australia separated
The line of demarcation is called Wallace’s line
Six biogeographic regions roughly correspond with major tectonic plates
Mid-ocean ridges: molten rock flows out of seams between plates and cools, forcing plates apart through seafloor spreading
Subduction zones: two plates meet and one slides under the other
Transform faults: two plates slide past each other
Dispersal also acts across continental land masses
Mainland can be the source of diversity that disperses into islands, but islands can also disperse into mainlands
Expansion and retraction of glaciers have shaped present-day vegetation communities
Expansion of glaciers shrink forests, especially near the poles
When glaciers retract, plants can expand their range
The Apalachicola valley served as a refugium for a number of species, including the Torreya pine, during the last ice age
There is more species diversity at the equator than at higher latitudes (latitudinal biodiversity gradient)
More than 25 mechanisms have been suggested for generating systematic latitudinal variation in these processes
These include explanations based on change, historical perturbation, environmental stability, habitat heterogeneity, productivity, and interspecific interactions
The tropics have 2.5 more land area than any other latitude range on Earth, and are the most thermally homogenous
This may decrease extinction and increase speciation
Higher productivity: more water and sunlight might provide more resources for plants and therefore other species
Larger area for reproductive isolation and speciation; larger and more widespread populations with lower extinction risk
The tropics have been more climatically stable over time, allowing them to accumulate more species over time
“A cradle and a museum”: many species originated in the tropics and dispersed to temperate regions; species that diversify in the tropics tend to stay there because of low extinction rates
Increasing environmental heterogeneity and more complex vegetation structures tend to support higher species diversity
Could be a factor in the tropics, but temperate regions also have forests and tend to have greater heterogeneity in some climatic factors
Intermediate disturbance hypothesis - a moderate level of disturbance leads to a mosaic of habitat types and higher levels of species diversity
Frequent disturbances caused by tree gaps in tropical forests combined with potentially greater effects of disturbance allows for persistence of gap specialists
Herbivores can reduce populations below their carrying capacities and promote species coexistence
High levels of herbivores and pathogens can promote biodiversity
Consumers locate abundant resources easily and their populations increase, which then leads to impacts of the consumer on the resource
Janzen-Connell hypothesis - seedling survival varies with distance from the parent tree, and this pattern seems especially strong in the tropics
Hubbell’s neutral theory states that species are all ecologically equivalent
New species that invade a community are likely to remain, and species disappear by extinction more or less at random
Large populations of trees distributed over large areas would likely build up large numbers of species over time
The null hypothesis assumes no environmental gradients and only a random latitudinal association between the size and placement of geographical ranges of species predict a peak of species richness at tropical latitudes
A tropical biodiversity peak might characterize icehouse worlds
Biomes
Alexander von Humboldt found that there were similarities in mountain structures globally
A biome can be defined by climate systems or ecological communities
Similar climates can lead to similar species
Tropical rain forests are defined by:
Large trees
Little annual variation (warm and wet with 2.5m+ annual rainfall)
High species diversity
Many epiphytes and vines
Old, highly weathered, nutrient poor soils
Arboreal fauna
Desert biomes are characterized by little rain (<25 cm) and high evaporation rates
Wide temperature fluctuations within a day
Plants have adaptations for drought avoidance (CAM, C4)
Low abundance but sometimes high diversity and endemism
Tropical savannas are characterized by a discontinuous tree layer and a continuous grass layer
Grass is perennial and C4
Very large animals are common
Frequent fires and intense herbivory maintain low tree cover
Distinct “wet” and “dry” forest
North central Florida is considered a subtropical savanna
Temperate deciduous forest is characterized by large trees that lose their leaves during winter
Seasonal temperature changes: warm and moderately rainy in the summer, cold winter
Fauna are often dormant or migratory during the winter
Boreal forest/taiga is characterized by coniferous trees
They are cool in the summer and cold in the winter with low annual precipitation
They have harsh, snowy winters
Snowmelt and low evaporation can make them wet
Fauna are dormant, migratory, or large
Fires are rare but major
They mostly occur in the northern hemisphere or at high altitudes
Tundra is cold and arid with a very short growing season
Permafrost limits rooting depth and drainage
Small shrubs, grasses, mosses
Seasonal dormancy or migration
Open ocean is the largest biome on Earth
Saline water
Light and nutrient limitation structure patterns of primary productivity; upwelling brings nutrients to surface layers
Phytoplankton are the dominant photosynthetic organisms and food chains can be long
Coastal zones are highly productive regions due to runoff from the land and nutrient upwelling
Salt marshes - temperate and higher latitudes
Mangrove swamps - tropics and subtropics
Intertidal zone - attached, high energy waves
Lakes and ponds tend to be geologically temporary features; there are relatively few ancient lakes, many located in rift valleys
Lakes stratify into distinct layers based on temperature; temperate lakes turn over in response to seasonal temperature changes
The lake environment changes as nutrients and sediments accumulate
Phytoplankton provide the base of the food web
Rivers and streams are characterized by variable flow
Regional climate influences streams by determining amounts and seasonality of precipitation and flow
Rivers drain watersheds, thus are highly influenced by land cover and land use change
Organic matter inputs from the land provide an important part of the base of the foodweb
Wetlands are transitional lands between terrestrial and aquatic systems where the water table is usually at or near the surface, or the land is covered by shallow water
Characterized by saturated soils, hydrophytic plants, standing water for at least part of the year
Includes marshes, swamps, peatlands, bogs, fens
Main limiting factors are low dissolved oxygen and fluctuating water levels
Can have high biodiversity value for plants and animals
Climate-tree cover relationship is not deterministic
Example: in South America, most savannas are characterized by tree cover rather than grass
Moisture and fire regulate tree abundance
Biomes are shaped by climate and evolutionary history
The earth is round so the sun hits the surface at different intensities
Warm air rises, cools, and falls
Warm air holds more moisture, and it releases it as precipitation as it falls
The ITCZ is wet because it is a low pressure zone where moist air is rising
30 degrees north and south tends to be desert due to the dry air coming in from the equator
Trade winds blow from east to west between 0 and 30 degrees, while westerlies blow from west to east between 30 and 60 degrees
Wind moves water and therefore nutrients around
The Earth has topography: as air rises in elevation, it cools and loses its water through precipitation, so rain shadows can develop on the leeward side of mountainous areas
Humid and wet on the side near a body of water, but desert on the other side
The earth is tilted to the ITCZ “wobbles” as the Earth revolves around the sun
The Earth’s orbit and axis vary
Milankovitch cycles are periodic orbital variations (ex. Precression, obliquity, eccentricity)
These are responsible for glaciation stages
Ice covers much of the northern hemisphere and parts of the southern
When water is frozen as ice, there is less precipitation
Glaciers scrape the topsoil off glaciated areas so the soil is younger in temperate areas
Primary Productivity
NDLVI is a measure of how “green” things are to estimate productivity
Primary production is the storage of energy through the formation of organic matter from inorganic carbon compounds; the power source for the ecosystem
Usually think of photoautotrophic production, which uses sunlight as a source of energy
Chemoautotrophs can obtain energy from the oxidation of electron donors and use CO2 and a carbon source
Gross primary productivity is the total rate of energy fixed by autotrophs in the ecosystem
A flux because it is an amount over time
Photosynthesis by primary producers
Net primary productivity is the total rate of energy accumulation by autotrophs in the ecosystem after they have met their own energetic needs
NPP = GPP - Ra (autotrophic respiration)
Net ecosystem productivity is the total rate of energy accumulation of the ecosystem after both autotrophs and heterotrophs have met their energetic needs
NEP = GPP - Ra - Rh (heterotrophic respiration)
NEP = Gpp - Re (ecosystem respiration)
NEP = NPP - Rh
Wetlands are the most productive, while deserts are the least productive
NPP can be expressed as g Carbon/m^2/yr
NPP increases with temperature and precipitation
Probably due to the length of growing season
More scatter at high temps, when temp is no longer limiting and other things are
Nutrient limitation can occur is response to variability in nutrient availability
Liebig’s Law of the Minimum states the nutrient in least supply relative to the plant’s requirement will limit the plant’s growth
We can measure NPP/NEP using a carbon dioxide sensor
You can measure the NEP of a whole forest using the biometric method that breaks NEP into several components:
Increments in wood, foliage, roots
Turnover of woody litter, foliar litter, wood litter
Loss via volatilization, exudation, DOC leaching, mycorrhizae
In general, NPP is allocated to different structural tissues
Usually, you try to measure:
Accumulation of biomass: diameter growth, harvest in grasslands
Detritus: litterfall traps
Herbivory: exclusion fences
Mesh bags, minirhizotron pictures, physical sorting of roots from soil
Eddy-covariance (eddy-flux) towers measure productivity of forests
As wind moves over a canopy, turbulent eddies are created that mix the air
Sensors measure the covariance between wind and CO2 concentrations: net flux of CO2 = downward flux - upward
The area that is measured isn’t fixed and is proportional to the height of the tower
Net ecosystem exchange is usually described as the net flux of CO2 between an ecosystem and the atmosphere
Terrestrial NPP can be measured using satellite imagery
NDVI = (NIR-red)/(NIR+red)
Vegetation has much higher reflection of infrared light than soil
Precipitation, temperature, and nutrients are the drivers of primary production
In aquatic systems:
Light penetrates through upper layers of aquatic systems (photic zone) where most production takes place
Photoinhibition can occur at high levels of light, but in general production increases with increasing light
Light infiltration tends to be higher in smaller systems with less organic matter loading from the watershed
Light is the highest in areas without a closed canopy of vegetation, can see opposite patterns of production in terrestrial vs aquatic ecosystems
In aquatic systems, increasing temperature can increase production, but can also increase respiration to a great degree
Warm temperatures can maintain high metabolic rates even under low nutrient conditions, as rapid nutrient cycling can be maintained
Respiration is more sensitive to temperature than production, so increasing temperatures
Nutrients can be highly limiting in aquatic systems
Total production appears to be the strongest predictor of eutrophication in lakes and oceans (mostly has to do with ratio of N:P)
We can measure aquatic NPP/NEP by measuring oxygen
Aquatic ecologists tend to report production in oxygen, while terrestrial ecologists report it in carbon
Sites of production include benthic vegetation, algae, biofilm, water column phytoplankton, sediment
In the summer, stratified layers are created in lakes (the surface is very warm, while the bottom is much cooler in comparison)
In the fall, winds and heat loss from the surface layer lead to deep mixing, bringing the bottom waters up to the surface
In the winter, the surface of the lake is the coldest and the bottom is warmer
Mixing occurs again in spring
Over a season or year, you can measure all the inputs and outputs of either organic or inorganic C
Input of C from fluvial, surrounding wetlands, and airborne pathways
Export through fluvial transport, gas exchange
Changes in storage in lake sediments and water column
Net balance of organic and inorganic C tells us if the lake is net autotrophic (fixes more C than it consumes) or net heterotrophic (consumes more C than it fixes)
Measured DO daily in the water to model GPP and R
Turbulence can affect DO
In marine ecosystems, primary production in the ocean is similar but most carbon is fixed by cyanobacteria and algae
Measured using chlorophyll a as a proxy
The El Nino Southern Oscillation (ENSO) cycle describes fluctuations in temperature between the ocean and atmosphere in the Equatorial Pacific
A decrease in east-west trade winds can lead to piling up of warmer water on the west coast of south america and decreased upwelling of cold water in nutrients
In the SE US, El Nino brings wetter than average conditions and La Nina brings drier, warmer winters
Secondary Production
Secondary production is all non-photosynthetic production regardless of its fate
Net secondary production is the rate of production of heterotroph biomass
NSP = Gross Secondary production - respiration
Energy used for growth and reproduction
Energy is lost in the environment to detritus, respiration, and egestion
Ingestion = Assimilation + Egestion
Egestion is the elimination of materials that were ingested but not assimilated
Ingestion is determined by metabolic demand
Assimilation = Respiration + Production + Excretion
Excretion is the elimination of materials that were ingested and assimilated but not retained for long-term growth or storage
Respiration is the loss of carbon due to maintenance costs
Production is the production of new biomass due to growth or reproduction
Metabolic rates increase with increasing temperatures and are higher for endotherms than ectotherms
Metabolic rates per unit mass decrease with increasing body size
Metabolic rates may fall over evolutionary time in food-poor habitats
Metabolic rate declines with body mass per gram
Many components of organismal physiology appears to scale with metabolic rate and thus be determined by body mass and temperature
Biomass production
Ontogenetic growth
Survival and mortality
Stoichiometry
These patterns can affect population and community dynamics, and can scale up to ecosystem processes
On average, about 10% of energy will be transferred from each trophic level to the one above it
In terrestrial systems, energy and biomass pyramids are typically similar since biomass is a good proxy for energy
Aquatic ecosystems can have inverted biomass pyramids with high consumption rates and low standing stock of biomass
Gross production efficiency = assimilation efficiency * production efficiency = production rate / ingestion rate
Allochthonous is used to describe carbon or other nutrients that come from outside the ecosystem
Primary and secondary production in an ecosystem can be subsidized by allochthonous resources from outside the ecosystem
Trophic efficiency is PN/PN-1, or the biomass production in trophic level N divided
Product of assimilation efficiency, production efficiency, and consumption efficiency
Consumption efficiency is the proportion of available biomass that is ingested
Typically higher in aquatic systems due to influences of predation, food quality, and plant defenses
Increases with resource nutrient concentration (higher for carnivores)
Assimilation efficiency is the proportion of ingested food that is assimilated, which is determined by the quality of the food and the physiology of the consumer
Much higher for carnivores where food quality is higher
Endotherms tend to digest food more thoroughly than ectotherms, leading to higher assimilation efficiencies
Production efficiency is the proportion of assimilated food used to produce new consumer biomass
Heavily influenced by consumer physiology
Higher production in ectotherms due to lower metabolic needs
Small endotherms tend to have lower production efficiencies since they have higher metabolic needs due to greater heat loss
Trophic efficiency is the amount of energy or biomass in one trophic level divided by the amount at the trophic level before it
Energy pyramid - rate of biomass production at each trophic level
Biomass pyramid - biomass stock at each trophic level
On average, 10% of energy will be transferred from each trophic level to the one above it
Biomass is usually a good proxy for energy in terrestrial systems
Aquatic systems can have an inverted period due to high consumption rates and relatively short lifespans of primary producers in aquatic systems
Duarte experimentally added nutrients to mesocosms in a coastal plankton community and found that autotroph biomass increase 50x with nutrient inputs, while heterotroph biomass increased 10x
Low nutrients resulted in inverted pyramid, while high nutrients yield an upward pyramid
Secondary production measures are often aquatic and empirical
Requires detailed measures of biomass production per area per time across all taxa of interest
In the Colorado River, invertebrate production declined downstream of tributaries
Fish demand was close to invertebrate production at downstream sites
Secondary production is a flux because it is an amount of production per time
As you go downstream, fish decline in invertebrate support and use terrestrial sources
Decomposition
Litter is dead plant material, while detritus is dead particulate organic matter
Necromass is dead organic matter of any type, including plant, animal, and microbial constituents
Soil organic matter (SOM) is detritus that is decomposed enough so that it is no longer recognizable
Litter and SOM pools including living microbial biomass, in addition to the “substrate”
Decomposition is the physical and chemical breakdown of detritus, including:
Leaching of soluble material
Fragmentation by animals
Chemical alterations by microbes
Nearly all carbon in detritus will eventually be returned to the atmosphere via heterotrophic respiration
Decomposing microbes have a growth efficiency of about 40%
Litter production is higher in areas where primary production is higher, but litter stocks are greatest in areas with low primary production due to slower decomposition rates
At equilibrium, stock = input flux/decomposition rate; input increases with NPP
The decomposition rate:
Increases with temperature because enzyme reaction rates and microbial metabolic rates increase with temperature
Increases with oxygen concentration which tends to be high in moist but well-drained soil (anaerobic decomposition is slower)
Depends on litter quality
Labile litter has low concentrations of lignin and chemical defense compounds and decomposes quickly
Recalcitrant litter has high concentrations of lignin and chemical defense compounds and decomposes slowly
Decomposition rates can be measured by placing mesh bags with litter of known mass on or under the ground surface
Periodically collect a sub-sample of bags and weigh the remaining litter
Decomposition is the turnover rate k: m(t) = m0 * e^-kt
Tiegs measured decomposition rates across biomes
They used cotton strips and measured decomposition as the tensile strength of cotton strips
In cold riparian climates, the decomposition rate was lower, but there was also a large amount of variation in warmer ecosystems
Temperature and precipitation are two of the biggest drivers of decomposition rate
Zhang did a meta-analysis and found that in general, decomposition rates increase with temp and annual precipitation and decrease with latitude
Litter quality is the most important direct regulator of litter decomposition at the global scale
Latitude, mean annual temperature, C:N ratio, and total nutrients account for 87.5% variation in decomposition
Litter decomposition rates are positively correlated with nutrient concentrations of N, P, K, Ca, and Mg, and negatively correlated with C:N ratios, lignin contents, and lignin:N ratios
High lignin:N means the leaf is “well-protected”
Benbow proposed the necrobiome framework
Necromass qualities include the size, nutrient content, and digestibility of the resource
Necrobiome structure consists of microbial communities (internal, external, substrate) and saprophage communities (invertebrate and vertebrate consumers)
Microbiome interactions and functions include:
Internal microbe and element translocation, molecular catabolism
External surface microbe and element translocation
Mixing of microbes and elements via trophic and physical pathways
Saprophage-mediated dispersal of microbes and elements into broader ecosystem
Microbe and element mixing across the necromass-substrate interface via trophic and physical pathways
Dispersal of microbes and elements into broader ecosystem via trophic and physical pathways
Wildebeest cross the Mara River during their migration, but they are crossing the river less often
Maybe climate change, overdevelopment
Litter bags full of wildebeest carcass material were left along the Mara river
Found that bone decomposed the slowest, while muscle decomposed the fastest
Decay rate can be calculated, which allows us to calculate days until 95% biomass lass
Soft tissue is rich in carbon and nitrogen, while bones have more phosphorus which decomposes slowly
Decomposition rates vary by bone type
High input rate divided by low decomposition rate leads to high standing stock of bones
Hippo feces have high carbon concentrations and decomposes faster when combined with wildebeest tissue
In Georgia, researchers found that nutrient additions of nitrogen and phosphorus to a stream decreased the length of time that terrestrial residence carbon stayed in the streams
Decomposition rates become faster