Community Ecology Exam 2

Lectures 5 - 8: Decomposers & Nutrient Cycling, Niche & Competition, Biodiversity, Climate & Soil

Scavengers

• consume carrion

• animals that eat animals that they don’t kill

  • usually; some scavengers “finish off” animals that are close to death

Carrion

easily digestible biomatter of dead animals

Detritovores

• consume detritus

• animals that eat what other things (scavengers) have left behind

Detritus

organic debris

Decomposers

• consume what’s left

• microscopic and very hard to digest organic material

• bacteria and fungi breaking down organic matter into inorganic matter and harvesting last iota of energy

Decomposers, detritovores, and scavengers

• consumers

• harvest last remnants of energy

• allow matter to be recycled

• prey and hosts

  • occasionally predator and parasite

Where is the line?

• scale

  • scavengers — consume large pieces of animal

    • ingestion

  • detritivores — consume medium-ish pieces of animal

    • ingestion

  • decomposers — consume organic molecules

    • secrete enzymes externally

• does it matter?

  • not usually

  • they perform the same functions

  • many species fit multiple categories

Stoichiometry

• Efficiency and residence time are affected by nutrient balance

• Nutrient balance varies by species and life stage

  • Diatoms need lots of Si

  • Vertebrates need lots of Ca and P

  • Faster growing organisms usually need more P

• If don’t obtain correct balance

  • Consume more -> reduces efficiency

  • Consume different things

  • Grow slower

Matter Cycling

• Cosmic inputs of matter are negligible … now

  • Loss of matter is negligible

• Matter on Earth can be treated as if in closed cycles

  • Each substance has own cycle

• Elements of life: CHNOPS

• Important parts of most cycles

  • Photosynthesis

  • Respiration

  • Decomposition

Water Cycling

• water evaporates

• falls as precipitation

• flows downhill

Anthropogenic impacts on hydrologic cycle

• impervious surfaces → more runoff, less filtration

• remove vegetation → more runoff

• removal of groundwater → reduced terrestrial water, more water cycling

• climate change → increased evaporation → increased precipitation

Carbon cycling

• photosynthesis removes CO₂ from the atmosphere and incorporates it into organic matter

• respiration releases C into the atmosphere as CO₂

• non-respired C can be buried

• buried C is released through weathering and volcanism

• atmospheric CO₂ diffuses into water

  • CO₂ + H₂O ←→ H₂CO₃ ←→H⁺ + HCO₃^- ←→ 2H⁺ + CO₃^2-

• CO₃^2- combines with Ca and is buried

• dissolved CO₂ diffuses into the atmosphere

Anthropogenic impacts on the carbon cycle

• extraction and combustion of buried C (fossil fuels)

• extraction and processing of buried CaCO₃ (concrete)

Nitrogen Cyling

• nitrogen fixation = conversion of N₂ into forms primary producers can use

  • requires a lot of energy

  • NH₃ → NH₄⁺ — via bacteria

  • NO₃ — via lightning and wildfire

• nitrification = NH₄⁺ → NO₂^- → NO₃^-

  • releases energy

• assimilation = NO₃^- incorporated into organic matter

• mineralization = organic matter → inorganic compounds

  • releases N from organic matter

  • N can then be assimilated

• denitrification = biologically usable N converted into N₂

  • NO₃^- → NO₂^- → NO

  • NO → N₂O → N₂

Anthropogenic impacts on the Nitrogen cycle

• NO produced from combustion of fossil fuels

  • NO + O₂ → NO₃^-

• Planting crops that promote nitrogen fixing

  • crop rotation

• direct production of nitrogen-containing fertilizers

Phosphorous cycling

• PO₄^3- containing rocks are weathered

• assimilation of PO₄^3- by primary producers

• mineralization of organic matter

• unbound PO₄^3- carried by water

• unbound PO₄^3- combines with Ca or Fe

• bound P precipitates and becomes part of sediment

• is buried

Anthropogenic impacts on phosphorous cycle

• mine PO₄^3- containing rocks to use as fertilizer

• PO₄^3- detergents

  • use is now banned in many countries

Terrestrial nutrient cycling

• nutrient cycling mostly occurs in soil (also removed in soil by primary producers)

• decomposition of plant material

  • water leaches minerals and small organic compounds

  • detritivores consume organic matter

  • bacteria and fungi break down organic molecules

• nutrients are leached from soil

• nitrogen fixing and weathering replenishes leached nutrients

Terrestrial decomposition

• aerobic

• occurs near primary producers

• affected by:

  • temperature

  • water

  • nutrient balance

• varies

Aquatic nutrient regeneration

• nutrient recycling mostly occurs in sediment (and removed all throughout the water column — especially at the surface)

• decomposition of plant material

  • same process as in terrestrial systems

  • different detritivores

  • bacteria and fungi are still decomposers

• decomposition of phytoplankton

  • much faster than plant decomposition (plants are hard to break down per primary consumers lectures)

  • mostly in sediments after dead cells have sunk

    • some occur in water column

Aquatic decomposition

• anaerobic

  • slow

• far from primary consumers

  • occurs in sediment

  • deeper water systems are less productive

• affected by

  • temperature

  • nutrient balance

• varies

• phytoplankton decomposition

  • so fast it can deplete dissolved oxygen in water column

Eutrophication

• excess production of organic carbon

  • too much primary production

• nutrient pollution = contamination of excess nutrient inputs

• eutrophication can occur naturally

• anthropogenic/cultural eutrophication is widespread

• decreased water quality

• hypoxia (low dissolved oxygen) / anoxia (no dissolved oxygen)

Hypoxia/anoxia

• hypoxia = reduced O₂

• anoxia = no O₂

• occurs naturally in most aquatic sediments

• rare in water column

  • “jubilee” in Alabama

• “dead zones”

  • mass mortality or exodus of aquatic fauna due to low dissolved oxygen

Stable isotopes in ecological research

• ≥ 80 elements have multiple stable isotopes

  • Tin (Sn) with 10 and xenon with 9 have the most

  • ≥ 19 elements have just 1 stable isotope

• CHNOS multiple stable isotopes

  • ¹²C, ¹³C, ¹H, ²H, ¹⁴N, ¹⁵N, ¹⁶O, ¹⁷O, ¹⁸O, ³²S, ³³S, ³⁴S, ³⁶S

• heavier isotopes react slower and form more stable covalent bonds

  • light isotopes concentrate in products and gases

  • heavier isotopes concentrate in reactants and solids/liquids

• all of this is generally speaking, specific reactions and conditions vary

Research uses of stable isotopes

• photosynthesis

  • enriched heavy C in C4 photosynthesis than C3

  • enriched heavy H in CAM compared to C3 & C4

• source tracking

  • ¹⁵N becomes enriched as you move to higher trophic levels

  • sources:

    • marine has more heavy N

    • terrestrial has more light N

  • anthropogenic sources are rich in heavy N

  • different geographical regions have distinct isotopic baselines

Radioisotopes in ecological research

• all elements have radioactive isotopes

• spike a source with radioisotopes and track where decay is occurring

• examples

  • ¹⁴C to measure photosynthesis

  • ²⁰⁴Hg to measure biomagnification

  • ³²P to track nutrient uptake and phosphorous cycling

  • ³⁵S to track sulfate reduction

The niche concept pre-1800

• religion, philosophy, naturalism

• each organism has a place within a harmonious system

• diet, habitat, behavior, distribution

• “natural beings are complementary and tend to a common purpose” - A. Pocherville

The niche concept 1800-1900

• interdependency of environment and organisms

• biotic relationships

• Darwin: organisms have a place in nature to which they are adapted by natural selection

Niche as a place

• “a recess in a wall especially for a statue” - Merriam-Webster

• Roswell Johnson 1910 and Joseph Grinnell 1913

• a place occupied by a species in the environment

• everything that conditions the existence of a species to a location

  • abiotic

  • biotic

• vacant niches can exist

Niche as a job

• Charles Elton 1927

• “the ‘niche’ of an animal means its place in the biotic environment, its relations to food and enemies

• based on location within food chains that combine to make a food cycle

  • location on trophic pyramid

• different organisms in different systems can occupy similar niches

Niche as a hypervolume

• G. Evelyn Hutchinson 1957

• niche is a space of environmental variables representing the limits of species viability

  • multidimensional space (hypervolume) that determines “where” a species can exist

• niche is an attribute of the species

• niche can be quantified

• fundamental niche = hypervolume niche that permits the species to exist

  • realized niche = region of the fundamental niche from which the species is not excluded by predators

Hypervolumes

• regions in more than 3 dimensions

  • line is 1D

  • square is 2D

  • cube is 3D

  • hypervolume is 4D+

• hypervolume coordinate systems

  • each axis is a separate variable

    • temperature

    • pH

    • moisture

    • PO₄^3-

    • NO₃^-

Niche now

• based on resources, abiotic conditions, and biotic interactions

• fundamental niche = range of abiotic conditions under which a species can persist

  • biotic interactions and limiting factors are not considered

  • facilitation?

• realized niche = actual conditions a species lives under

  • all environmental and biotic factors are considered

Facilitation

• positive, non-harmful interaction in which one species improves the fitness of the other

• mutualism = all species benefit

• commensalism = at least one of the involved species is not impacted

• can work through

  • direct interaction

  • indirect interaction

    • abiotic

    • biotic

Facilitation and niche

• facilitation may counteract negative biotic interactions

  • refuge from predation

  • removal of parasites

• facilitation may allow persistence outside of non-facilitated niche space

  • expansion of fundamental niche

  • OR extension of realized niche beyond fundamental niche

  • examples:

    • nurse plants

    • macroalgae in rocky intertidal habitats

Range of tolerance

• “better” conditions are needed for reproduction than growth

• “better” conditions are needed for growth than survival

• range of reproduction heavily affects occurrence of species

  • individuals can disperse to areas with limited reproductive potential

Environmental gradient

• populations will not be found where the species cannot survive

• population size will be limited in regions of physiological stress

• population size will be highest in regions where conditions are optimum

Example of gradient on a small scale

grass species:

• too close to a lake/pond → too much water for species to survive

• medium distance from the water → species can survive, grow, and reproduce

• too far from the lake/pond → not enough water for species to survive

Interspecific competition

• species A sequesters a resource before species B

  • species A and species B are both negatively affected

  • but species B is more negatively affected

• species A may

  • be better able to sequester that resource

  • need less of the resource

  • take resource from species B

• competitive exclusion = a species is excluded from a habitat due to competition with another species

Niche and competition

• competition occurs where niches overlap

• competition prevents utilization of full niche hypervolume

Coexistence of competitors: resolving the plankton paradox

• environment is neither isotropic nor unstructured

  • fluid motion

    • chaotic

    • wind-driven

  • light attenuation

  • changing nutrient concentrations

  • daily, seasonal, annual variation

• grazing/predation

  • selective by shifting zooplankton assemblages

  • viruses

• environment never equilibrium

• natural selection favors reduced competition

Environment and competition

• abiotic factors influence competitive outcomes

• adaptations to abiotic factors determine “winner”

  • niche partitioning

Natural selection and competition

• natural selection leads to minimization of competition

• competitive exclusion

• niche partitioning

  • specialization

  • character displacement

Natural selection

• direction selection: selection favors individuals showing an extreme phenotype (underdominance)

• disruptive selection: selection favors individuals at both extremes of a phenotype (underdominance)

• stabilizing selection: selection favors individuals with an intermediate phenotype (overdominance)

Competitive separation

• allopatric = geographic separation

• sympatric = without geographic separation

• character displacement

Ecological guilds and functional groups

• species with similar niches

  • through using similar resources = ecological guild

  • through feeding in similar manners = functional group

• same guilds

  • spiders and bats

• same functional group

  • mosquito and aphids

• same guild and same functional group

  • barnacles and mussels

Ecological guilds

• defined by resource use

  • foraging/feeding guilds

  • habitat based guilds

  • pollinator guilds

• often competitors

• functional redundancy

Functional groups

• defined by method of resource acquisition or ecosystem function

Biodiversity

• aka diversity, biological diversity, organismal diversity, ecological diversity

• variation within and between organisms and ecosystems

Categories of diversity

• genetic

  • allele ratios

• taxomonic — shared ancestry

  • taxa that share a common ancestor

  • usually species

• community/ecosystem — shared geography

  • place and time

  • habitat and abiotic conditions

• guild — shared resources

  • exploitation of shared resources

  • ex. detritivores

• ensemble — shared ancestry, geography, and resources

  • taxa that share a common ancestor, inhabit the same habitat, and utilize the same resource(s)

  • ex. herbivorous reef fish

Scales of diversity

• inventory diversity — measured diversity

  • point diversity, α-diversity, γ-diversity, & ε-diversity

• differential diversity — comparisons of measured diversity

  • pattern diversity β-diversity & δ-diversity

• alpha (α) — local diversity

  • within a habitat or ecosystem

• beta (β) — comparison between two habitats or ecosystems

  • comparison of 2 α diversities

• gamma (γ) — regional diversity

  • large scale diversity covering multiple habitats

Point and Pattern Diversity

• within/between sample diversity

  • smallest scale

• point diversity = diversity from a single sample

• pattern diversity = variation in diversities from samples taken within a single habitat

• useful for examining diversity within a habitat

• multiple of these samples combined to determine α-diversity

α-diversity

• Diversity of a defined assemblage, habitat, or system

  • Geographic scale determined by researcher

• Diversity from a set of samples

  • From the same habitat

• Expressed as

  • Species richness

  • Species evenness

  • Diversity index

β-diversity

• Comparison of α-diversity between 2 habitats or systems

  • Or between 2 time periods

• Species change or replacement

  • Species turnover

• Habitats/systems being compared must be measured in the same scale

  • Scale must be appropriate for the species

• Expressed as

  • Ratios

    • β = γ / α

    • α species richness / mean α species richness

  • β species richness = number of unique species

γ-diversity

• Diversity of a large region encompassing several habitats and systems

  • Landscape

  • Geographic scale determined by researcher

• Combination of α-diversities

• Same measurement methods as α-diversity

• Affected by α & β

  • Habitats with similar α-diversity but different species will yield high γ-diversity

δ-diversity

• Delta diversity

• Comparison of γ -diversity between 2 regions

• Species change or replacement

• Scales must be similar and appropriate

• Same methods as β-diversity

ε-diversity

• Epsilon diversity

• Larger scale than γ-diversity

  • Continental or large geographic province

• Same measurement methods as α & γ –diversities

  • If you can measure abundances on that scale

  • In practice usually species richness

• Very common to look at Family (instead of species) diversity

Hyperdominant / oligarchs

• Occurs when a small subset of species represent most individuals

  • “Most” = >~50%

• γ & ε –diversity only

  • Does not apply to α-diversity

• Demonstrated in tropical forests

  • More research needed for other habitats and organisms

Community vs assemblage

• Community – group of populations living in the same area and interacting with one another

• Assemblage – group of species that are taxonomically related and live in the same area

  • Component of the community

  • Most biodiversity research focuses on assemblages

Habitat/community boundaries

• Zonation – distribution of organisms across an environmental gradient

  • Arrangement of species in a habitat / across habitats

  • Species composition along the landscape

• Boundaries may be clearly defined or shade from one zone into another

  • Lake vs forest

  • Elevation zones as one ascends a mountain

Habitat edges

• Changes in population and community structure at the boundary between habitats

  • Zone that extends into both habitats

  • Ecotone – sharp change in environmental conditions over a short distance

    • Large change in species composition

• Promotes interaction among different community types

• Reduces suitable habitat because part

of the habitat is habitat edge

Species distributions

• Why are species found where they are?

  • Niche

• Environmental conditions

• Resource availability / primary productivity

• Keystone species

• Dispersal / immigration

• Disturbance

• Climate change

• Continental drift / plate tectonics

Species-area relationship

• Number of species increases area examined increases

• Increase area by 10 times, double number of species

  • Darlington’s rule

• S = cAz

  • S = number of species, A = area

  • c and z are fitted constants

  • log(S) = log(c) + z log(A)

    • log(c) = y-intercept, z = slope

Species and Area

• More habitat diversity as area examined increases

  • Different species adapted to different habitats -> higher β/δ –diversity

• Larger areas can fit more and larger species

• Equilibrium model of island biogeography

Equilibrium model of island biogeography

• Island biogeography + extinction rate

• Number of species present is dependent on immigration of new species & local extinction of existing species

  • Ŝ = IP / (I + E)

    • Ŝ = equilibrium number of species

    • I = immigration rate, E = local extinction rate

  • P = number of species in source pool = maximum number of species

• Turnover rate = replacement rate of species

  • IE / (I + E)

Biodiversity and latitude

• More species near equator, fewer near poles

• Ecological heterogeneity

• Land – solar energy and precipitation

• Ocean – water temperature

Ecosystem functions and services

• Ecosystem functions – natural processes and interactions occurring within an ecosystem

  • Soil formation, nutrient cycling, pollination

• Ecosystem services – benefit of ecosystem functions derived by humans

  • Air purification, flood control, seafood

• Much but not complete overlap

Biodiversity and ecosystem function

• more diversity → more and better ecosystem function

  • ecosystem functions do not exist without organisms

How does increased diversity lead to better function?

• Must have an organism to perform function

• Niche partitioning

• Functional redundancy

• Increased resilience

  • Resilience = speed at which a system returns to its original state after a perturbation

Intrinsic value of biodiversity

• inherent worth

• species and ecosystems have value by existing

  • independent of human use

• aesthetic value

• right to exist

• moral obligation to ensure species continue to exist

Instrumental value of biodiversity

• Benefit to humans

  • Economic value

• Supporting services – allow ecosystems to exist

• Regulating services – control abiotic environment

• Provisioning services – harvestable resources

  • Ecosystem goods

• Cultural services – aesthetic, spiritual, and recreational value

Valuation of ecosystem services (1997)

• Constanza et al. 1997

  • $33 trillion in 1994 $

  • 1.8 times global net production

• NOT TO BE TAKEN AT FACE VALUE

Extinction

• Complete eradication of a taxon

  • Extinct in the wild = taxon is only present in captivity

  • Functionally extinct = taxon can no longer perform its role in the ecosystem

• Background extinction rate / normal extinction rate

  • Varies by group

• Mass extinctions – event in which > 75% of known existing species become extinct

  • “Event” = < 2,000,000 years

  • 5 mass extinctions in last 500 million years

• Current extinction rate

  • 6th mass extinction?

Threats to biodiversity

• Habitat loss – destruction or degradation of habitat

• Overharvesting – removing organisms at unstainable rates

• Pollution – addition of a harmful substance or energy to an environment

• Climate change – long-term shift in temperature and weather patterns

• Introduced species – transportation of an organism to a location it is not native to

Habitat loss

• Destruction or degradation of habitat

• Most impactful

• Land use changes and over harvesting

• Habitat fragmentation

Overharvesting

• Removing organisms at unstainable rates

• Harvesting methods become more effective

• Many regulations allow harvesting at unsustainable rates

  • Subsidies to otherwise non-profitable harvests

Pollution

• Addition of a harmful substance or energy to an environment

• Chronic vs acute

• Point source vs nonpoint source

• Single species impacts

• Multispecies impacts

  • Biomagnification – increase in the concentration of a substance as it moves to higher trophic levels

• Habitat loss

Climate change

• Long-term shift in temperature and weather patterns

• Alters the location of species fundamental niche

  • Populations move if possible

  • Alters community interactions

• Habitat loss

Introduced species

• Transportation of an organism to a location it is not native to

• Competitors, predators, pathogens to native species

• Habitat loss

• Not always harmful

• … but leads to increase in diversity?

  • Biotic homogenization

  • everything becomes the same in the end, so is actually an overall loss of diversity

Conservation of Biodiversity

• Ecological conservation = the practice of protecting and restoring species, habitats, and ecosystems

  • Includes governance of human usage

• Mitigate the threats to biodiversity

• Common thread of all threats: human population and resource acquisition

Habitat protection and restoration

• Biggest threat to biodiversity is habitat loss

• Challenges

  • Protected area must be large enough

  • Some populations’ requirements change

  • Some populations migrate

  • Societal needs

• Most successful

  • Cover large areas

  • Low human density

  • Support of local community

  • Enforcement

• Restoration – restoring habitat to natural conditions

  • Remove invasive species

  • Remove pollutants

  • Remove artificial structures

    • Restore water flow

  • Reintroduce native species

Reduced harvesting

• seems simple

• impacts livelihoods

• usually successful

Species reintroductions

• captive rearing of individuals to be released

• very expensive

• mixed success

Weather and climate

• Weather = short-term local atmospheric conditions

  • Day-to-day temperature, precipitation, etc.

• Climate = long-term “average” atmospheric conditions

  • “Average” and variability of weather

• “Climate is what you expect, weather is what you get.”

Factors affecting climate

• Latitude – proximity to the equator

• Atmospheric circulation – large-scale air movement

• Topography – mountains and valleys

• Continentality – landmasses as well as distance to and size of water bodies

• Oceanic circulation – large-scale water movement

Latitude

• Solar energy reaching Earth’s surface decreases as latitude increases

• Angle – low angle spreads the radiation over a larger area

• Atmosphere – absorbs, scatters, and reflects radiation

Global net radiation

• unequal heating of the Earth’s surface

• the major cause of climate, and weather, is the uneven heating of the Earth’s surface

Movement of heat

heat moves from warmer/hotter areas to cooler/colder areas

Earth’s rotation

causes the Coriolis effect:

• in the northern hemisphere, increasing deflection of moving water parcel to the right

• equator has no deflection

• in the southern hemisphere, increasing deflection of moving water parcel to the left

Atmospheric circulation

• 6 convection cells

• Persistent high- and low-pressure areas

• Predictable winds

Hot deserts

mostly found at 30º N and 30º S due to warm, dry air circulating in from Hadley cells

Topography

• Physical features of a landscape

• Mountains

• Mountains force air up

  • As air rises, it cools

  • Cool air can hold less moisture

  • Precipitation forms and falls

  • Air descending the mountain is dry

• high elevations are cooler

Continentality and jet streams

• Coastal areas are cooler and wetter with small temperature ranges

• Center of continents have large temperature ranges

  • Often drier

• Air masses = large body of air with mostly uniform temperature and humidity

  • Defined by source

  • More time over source = more likely will acquire properties of source

• Jet streams = narrow bands of strong wind in upper atmosphere

  • West to east

  • Persistent but strength varies

  • Location shifts N or S

Oceanic circulation

• Energy from wind + Coriolis effect

• 5 major ocean gyres

  • North Atlantic

  • South Atlantic

  • North Pacific

  • South Pacific

  • Indian

• Transfers energy from tropics to high latitudes

European climate

• climate in Europe is generally much more mild than similar latitude in North America and Central and East Asia

• this is because of jet streams that pick up warm air heated by the warm water of the Gulf Stream current that bring warm water into the Atlantic from the Gulf of Mexico

Climate change

long term shifts in temperatures and weather patterns

Some ecological consquences

• Increased mortality

  • 20-30% of evaluated species are at risk of extinction if temperatures reach projected 2100 levels

• Timing of seasonal cycles

• Habitat loss

• Range shifts

  • Parasites included

• Food web disruptions

Synonyms for soil

Earth, ground, dirt, loam, turf, humas, marl, clay, dust, mud, topsoil, muck, mold, silt, clod, sand, subsoil, kaolin, alluvium, loess, sediment, colluvium, gley, substrate, detritus, gault, blackland, shingle, substratum, guck, duff

Soil

• Loose surface material that covers most land

• Unconsolidated mixture of mineral particles, organic matter, water, and air that covers the Earth's surface and supports plant life

Soil formation: weathering

• Physical weathering breaks parent material into smaller pieces

  • Frost weathering

  • Thermal stress

  • Biomechanical weathering

• Chemical weathering and transformation alters the minerals present

  • Dissolution

  • Oxidation

  • Hydration

  • Biochemical weathering