Ecosystem Services, Species Interactions, Trophic Levels, Island Biogeography, Species Types, Survivorship, Invasive/Endangered Species, Carrying Capacity, Ecological Tolerance, Natural Disruptions

Ecosystem Service

  • A benefit provided to humans by the natural environment.
    • Types:
    • Provisional
    • Regulating
    • Cultural
    • Supporting

Chesapeake Bay Watershed

  • 6 state region that drains into a series of streams/rivers and eventually into Chesapeake Bay
  • Mix of fresh and salt water + nutrients in sediment make estuary habitats like the salt marshes in the bay highly productive
  • Estuaries & wetlands provide ecosystem services:
    • Tourism revenue - hotels, restaurants, permits
    • Water filtration (grass roots trap pollutants)
    • Habitats for food sources (fish & crabs)
    • Storm protection (absorbing & buffering floods)

Provisional Services

  • A service extracted from nature.
    • Ex: Timber, Fossil Fuels, etc.

Regulating Services

  • A service that moderates natural phenomena.
    • Ex: Coral Reefs slowing and weakening storms, Bogs stopping flooding.

Cultural Services

  • Cultural ecosystem services are the non-material benefits that people obtain from ecosystems through recreation, tourism, intellectual development, spiritual enrichment, reflection and creative and aesthetic experiences.
    • Ex: Parks, Spiritual Benefits, Aesthetics

Supporting Services

  • Services that provide support all other ecosystem services.
    • Ex: Photosynthesis, Biogeochemical Cycles

Ecosystems: Learning Objective ERT-1.A

  • Explain how the availability of resources influences species interactions.

Essential Knowledge ERT-1.A.1

  • In a predator-prey relationship, the predator is an organism that eats another organism (the prey).

Essential Knowledge ERT-1.A.2

  • Symbiosis is a close and long-term interaction between two species in an ecosystem.
    • Types of symbiosis include mutualism, commensalism, and parasitism.

Essential Knowledge ERT-1.A.3

  • Competition can occur within or between species in an ecosystem where there are limited resources.
    • Resource partitioning- using the resources in different ways, places, or at different times-can reduce the negative impact of competition on survival.

Ecosystem Basics

  • Individual = one organism (elk)
  • Pop. = group of individuals of same species (elk herd)
  • Community = all living organisms in an area
  • Ecosystem = all living & nonliving things in an area (plants, animals, rocks, soil, water, air)
  • Biome = the plants and animals found in a given region (determined by climate)
    • Ex: (tropical rainforest)

Organism Interactions

  • Mutualism: relationship that benefits both organisms (coral reef) (+/+)
  • Competition: organisms fighting over a resource like food or shelter; limits pop. size
  • Predation: one organism using another for energy source (hunters, parasites) (+/-)
  • Commensalism: relationship that benefits one organism & doesn’t impact the other (birds nest in trees) (+/0)

Predation (+/-)

  • True predators: (carnivores) kill and eat prey for energy (leopard & giraffe)
  • Herbivores: (plant eaters) eat plants for energy (giraffe & tree). Herbivores are technically predators
  • Parasites: use a host organism for energy, often without killing the host & often living inside host
    • Ex: mosquitoes, tapeworms, sea lamprey
  • Parasitoids: lay eggs inside a host organism; eggs hatch & larvae eat host for energy
    • Ex: parasitic wasps, bot fly

Symbiosis

  • Sym = together | bio = living | osis = condition
  • Mutualism: Organisms of diff. species living close together in a way that benefits both, includes commensalism and parasitism.
  • Any close and long-term interaction between two organisms of different species
    • Mutualism (+/+), commensalism (+/0), and parasitism (+/-) are all symbiotic relationships
  • Coral (animals) provide reef structure & CO_2 for algae; algae provide sugars for coral to use as energy
  • Lichen = composite organism of fungi living with algae; algae provide sugars (energy) & fungi provides nutrients

Competition

  • Resource partitioning: different species using the same resource in diff. ways to reduce competition
    • Reduces population size since there are fewer resources available & fewer organisms can survive
  • Temporal partitioning: using resource @ different times, such as wolves & coyotes hunting @ different times (night vs. day)
  • Spatial partitioning: using different areas of a shared habitat (different length roots)
  • Morphological partitioning: using different resources based on diff. evolved body features

Trophic Levels & The 10% Rule

Objectives/EKs/Skills

  • LEARNING OBJECTIVE ENG-1.B
    • Explain how energy flows and matter cycles through trophic levels.
    • SUGGESTED SKILL 1.B
    • Concept Explanation: Explain environmental concepts and processes.
    • ESSENTIAL KNOWLEDGE ENG-1.B.1
    • All ecosystems depend on a continuous inflow of high-quality energy in order to maintain their structure and function of transferring matter between the environment and organisms via biogeochemical cycles.
    • ESSENTIAL KNOWLEDGE ENG-1.B.2
    • Biogeochemical cycles are essential for life and each cycle demonstrates the conservation of matter.
    • ESSENTIAL KNOWLEDGE ENG-1.B.3
    • In terrestrial and near-surface marine communities, energy flows from the sun to producers in the lowest trophic levels and then upward to higher trophic levels.
  • LEARNING OBJECTIVE ENG-1.C
    • Determine how the energy decreases as it flows through ecosystems.
    • SUGGESTED SKILL 6.C
    • Mathematical Routines: Calculate an accurate numeric answer with appropriate units.
    • ESSENTIAL KNOWLEDGE ENG-1.C.1
    • The 10% rule approximates that in the transfer of energy from one trophic level to the next, only about 10% of the energy is passed on.
    • ESSENTIAL KNOWLEDGE ENG-1.C.2
    • The loss of energy that occurs when energy moves from lower to higher trophic levels can be explained through the laws of thermodynamics.

Conservation of Matter & Energy

  • Matter & energy are never created or destroyed; they only change forms
    • Ex: Tree dies & the C/N/H2O/P are returned to the soil & atmosphere
    • Ex: Sun rays (light energy) hit leaves & are converted into glucose (chemical energy)
  • 1st law of thermodynamics: energy is never created or destroyed
  • Biogeochem. cycles demonstrate conservation of matter (C/N/H2O/P)
  • Food webs demonstrate conservation of energy
    • Ex: When a rabbit eats a leaf, the energy from the leaf (glucose) is transferred to the rabbit & stored as body tissue like fat/muscle

2nd Law of Thermodynamics

  • Each time energy is transferred, some of it is lost as heat
  • Applied to food webs: the amount of useable energy decreases as you move up the food chain (organisms use up most of it for movement, development, etc.)
  • 10% Rule: in trophic pyramids, only about 10% of the energy from one level makes it to the next level; the other 90% is used by the organism & lost as heat
  • Because available energy decreases with each step up the food chain, a trophic pyramid (troph = nourishment or growth) is used to model how energy moves through an ecosystem

Trophic Levels & 10% Biomass

  • Producers (plants) “produce”- really convert sun’s light energy into chemical energy (glucose)
  • Primary Consumers: animals that eat plants (herbivores)
    • 10% rule also applies to biomass (or mass of all living things at each trophic level)
    • Since energy is needed for growth & only 10% of energy transfers from one level to the next, only 10% of the biomass of the previous trophic level can be grown/supported by the available energy
  • Secondary Consumers: animals that eat primary consumers or herbivores (aka - carnivores & omnivores)
  • Tertiary Consumers: animals that eat secondary consumers or carnivores & omnivores (aka - top/apex predators)

Calculating Biomass & Energy

  • To calculate biomass or energy available at the next level up, move the decimal place one spot to the left (or divide by 10)

Food Chains and Food Webs

Objective/EKs/Skill

  • LEARNING OBJECTIVE ENG-1.D
    • Describe food chains and food webs, and their constituent members by trophic level.
    • SUGGESTED SKILL 2.A
    • Visual Representations: Describe characteristics of an environmental concept, process, or model represented visually.
    • ESSENTIAL KNOWLEDGE ENG-1.D.1
    • A food web is a model of an interlocking pattern of food chains that depicts the flow of energy and nutrients in two or more food chains.
    • ESSENTIAL KNOWLEDGE ENG-1.D.2
    • Positive and negative feedback loops can each play a role in food webs. When one species is removed from or added to a specific food web, the rest of the food web can be affected.

Food Web Basics

  • Shows how matter & energy flow through an ecosystem, from organism to organism
  • When one organism preys on (eats) another, the matter (C/N/H2O/P) and energy (glucose, muscle tissue, etc.) are passed on to the predator
  • Arrows in food webs indicate direction of energy flow (point to the org. taking in the energy)

Food Web vs. Chain

  • Food chains just show one, linear path of energy & matter
  • Food webs have at least 2 different, interconnected food chains
  • Webs show that organisms can exist at different trophic levels
    • grass → hare → owl (sec. cons.)
    • grass → grasshopper → robin → owl (tert. cons.)

Theory of Island Biogeography & Biodiversity

Objective/EKs/Skill

  • LEARNING OBJECTIVE ERT-2.D
    • Describe island biogeography.
    • SUGGESTED SKILL 1.A
    • Concept Explanation: Describe environmental concepts and processes.
    • ESSENTIAL KNOWLEDGE ERT-2.D.1
    • Island biogeography is the study of the ecological relationships and distribution of organisms on islands, and of these organisms' community structures.
    • ESSENTIAL KNOWLEDGE ERT-2.D.2
    • Islands have been colonized in the past by new species arriving from elsewhere.
  • LEARNING OBJECTIVE ERT-2.E
    • Describe the role of island biogeography in evolution.
    • ESSENTIAL KNOWLEDGE ERT-2.E.1
    • Many island species have evolved to be specialists versus generalists because of the limited resources, such as food and territory, on most islands. The long-term survival of specialists may be jeopardized if and when invasive species, typically generalists, are introduced and outcompete the specialists.

Island Biogeography

  • The larger the island, the greater the ecosystem diversity
    • Greater ecosystem diversity = more food & hab. resources
    • More niches, or “roles” organisms can play in the ecosystem Larger Islands support more total species
  • Islands closer to the “mainland” support more species
  • Two basic “rules” or observations of Island Biogeography:
    • Easier for colonizing organisms to get to island from mainland
    • More colonizing organisms = more genetic diversity in new pop.

Biodiversity Basics

  • Diversity of life forms in an ecosystem; measured on 3 different levels:
    • Genetic diversity: how different the genes are of individuals within a population (group of the same species)
    • Species diversity: the number of diff. species in an ecosystem
    • Ecosystem diversity: the number of diff. habitats available in a given area
  • Higher biodiversity = higher ecosystem/ population health

Species Richness & Evenness

  • Richness (r) is just the total number of different species found in an ecosystem
  • Evenness is a measure of how all of the individual organisms in an ecosystem are balanced between the different species
  • High (r) is generally a good sign of ecosystem health (more species means more quality resources like H2O & soil)

All forms of Diversity is Beneficial

  • Higher biodiversity = Increased ecosystem resilience
    • The more genetic diversity in a pop. the better the population can respond to env. Stressors like drought, disease, or famine
    • More gen. div. = higher chance that some of the individuals in a pop. have traits that allow them to survive the env. Stressor
  • Resilience = the ability of an ecosystem to return to its original conditions after a major disturbance (wind storm, fire, flood, clear-cutting, etc.)

Bottleneck Event

  • Bottleneck events reduce genetic diversity
    • An env. disturbance (natural disaster/human hab. destruction) that drastically reduces pop. size & kills organisms regardless of their genome
  • Surviving pop. is smaller and because individuals died randomly, it doesn’t represent the genetic diversity of the original pop.
  • Because the pop. is smaller & less genetically diverse, it’s even more vulnerable to future env. disturbances

Inbreeding Depression

  • Inbreeding is when organisms mate with closely related “family” members
    • Smaller populations are more likely to experience inbreeding (difficult to find non-related mate)
  • Leads to higher chance of offspring having harmful genetic mutations because they’re getting similar genotypes from both parents
    • Ex: Florida panther pop. decreased down to 30 in 1900s due to hunting & hab. loss. Inbreeding depression = kinked tails, heart defects, low sperm count, (saved in 95’ by pumas from Texas)

Ecosystem Resilience

  • Resilience = the ability of an ecosystem to return to its original conditions after a major disturbance (wind storm, fire, flood, clear-cutting, etc.)
  • Higher species diversity = higher ecosystem resilience
    • High sp. div means more plant species to repopulate disturbed ground, anchor soil, and provide food & habitat for animal species

Evolution on Islands

  • Islands have limited space & resources, creating unique conditions for evolution
    • More pressure for species to adapt to narrower niches (more specific food/hab.)
  • Adaptive radiation = single species rapidly evolving into several new species to use diff. resources & reduce competition
    • Ex: Galapagos Finches
    • Different beaks quickly evolve to fit variety of different food sources on Island
    • Single colonizing species from mainland quickly evolves to many slightly different species to adapt to new island cond.

Fitness & Adaptation

  • All populations have some genetic diversity, or variability in genomes of individuals; Genetic diversity exists because:
    • Random mutations while DNA is being copied create new traits
    • Crossing over in parent chromosomes creates new combinations of genes (and therefore traits)
  • Adaptation: a new trait that increases an organism’s fitness (ability to survive and reproduce)

Adaptation & Natural Selection

  • Natural selection : organisms that are better adapted to their env. survive and reproduce more offspring
    • Individuals with adaptations pass them on to offspring & individuals without adaptations die off, which leads to the entire population having the adaptation over time (evolution)
    • Selective pressure/force: the environmental condition that kills individuals without the adaptation
    • Predation (hawk) = selective pressure

Environmental Change & Evolution

  • The environment an organism lives in determines which traits are adaptations
    • As environments change, different traits may become adaptations & old traits may become disadvantages
    • Ex: a drought can kill off finches with smaller beaks, making larger beaks for cracking harder seeds an adaptation

Pace of Evolution

  • The more rapidly an env. changes, the less likely a species in the env. will be to adapt to those changes
    • If the pace of env. change is too rapid, many species may migrate out of the env. or die-off completely
    • Ex: if the ocean warms too quickly, many species of fish may not be able to migrate before they run out of oxygen and suffocate
  • The more genetic diversity in a population, the better they’re able to adapt to env. change (higher chance that some individuals have good mutations)
  • The longer the lifespan of the organism, the slower the rate of evolution
    • Ex: bacteria & viruses can adapt and evolve in days; Humans evolution = thousands-mil. years

Specialist vs. Generalist Species

  • Both are in the same family Musteloidea
    • Red Pandas can only eat Bamboo
    • Raccoons eat all types of food.

LEARNING OBJECTIVE ERT-3.A

  • Identify differences between generalist and specialist species.
    • ESSENTIAL KNOWLEDGE ERT-3.A.1
    • Specialist species tend to be advantaged in habitats that remain constant, while generalist species tend to be advantaged in habitats that are changing.

Specialists

  • Smaller range of tolerance, or narrower ecological niche makes them more prone to extinction
    • Specific food requirements (bamboo)
    • Less ability to adapt to new conditions

Generalists

  • Larger range of tolerance, broader niche makes them less prone to extinction & more likely to be invasive
    • Broad food req.
    • High adaptability

K-selected & r-selected species

LEARNING OBJECTIVE ERT-3.B

  • Identify differences between K- and r-selected species.
    • ESSENTIAL KNOWLEDGE ERT-3.B.1
    • K-selected species tend to be large, have few offspring per reproduction event, live in stable environments, expend significant energy for each offspring, mature after many years of extended youth and parental care, have long life spans/life expectancy, and reproduce more than once in their lifetime. Competition for resources in K-selected species' habitats is usually relatively high.
    • ESSENTIAL KNOWLEDGE ERT-3.B.2
    • r-selected species tend to be small, have many offspring, expend or invest minimal energy for each offspring, mature early, have short life spans, and may reproduce only once in their lifetime. Competition for resources in r-selected species' habitats is typically relatively low.
    • ESSENTIAL KNOWLEDGE ERT-3.B.3
    • Biotic potential refers to the maximum reproductive rate of a population in ideal conditions.
    • ESSENTIAL KNOWLEDGE ERT-3.B.4
    • Many species have reproductive strategies that are not uniquely r-selected or K-selected, or they change in different conditions at different times.
    • ESSENTIAL KNOWLEDGE ERT-3.B.5
    • K-selected species are typically more adversely affected by invasive species than r-selected species, which are minimally affected by invasive species. Most invasive species are r-selected species.

K-selected - “quality”

  • Few offspring, heavy parental care to protect them
  • Generally have fewer reproductive events than r-strategists
    • Ex: most mammals, birds
  • Long lifespan, long time to sexual maturity = low biotic potential = slow pop. growth rate
    • More likely to be disrupted by env. change or invasives

R-selected - “quantity”

  • Many offspring, little to no care
  • May reproduce only once, but generally reproduce many times throughout lifespan
    • Ex: insects, fish, plants
  • Shorter lifespan, quick to sexual maturity = high biotic potential = high pop. growth rate
    • More likely to be invasive
    • Better suited for rapidly changing env. conditions

K-selected

  • Low biotic potential (rep. rate) = hard for pop. to recover after a disturbance (env. change)
  • High parental care means death of parent = death of offspring
  • Invasives (usually r) outcompete for resources with high biotic potential & rapid pop. growth
  • Less likely to adapt & more likely to go extinct

R-selected

  • High biotic potential (rep. rate) = more rapid pop. recovery after disturbance
  • Low parental care means death of parent doesn’t impact offspring
  • Not as impacted by invasive species since their pop. grow quickly
    • More likely to be the invasive
  • Larger pop. & faster generation time = higher chance of adaptation & lower chance of extinction

Survivorship Curves

LEARNING OBJECTIVE ERT-3.C

  • Explain survivorship curves.
    • ESSENTIAL KNOWLEDGE ERT-3.C.1
    • A survivorship curve is a line that displays the relative survival rates of a cohort-a group of individuals of the same age-in a population, from birth to the maximum age reached by any one cohort member. There are Type I, Type II, and Type III curves.
    • ESSENTIAL KNOWLEDGE ERT-3.C.2
    • Survivorship curves differ for K-selected and r-selected species, with K-selected species typically following a Type I or Type II curve and r-selected species following a Type III curve.

Survivorship Curve:

  • Line that shows survival rate of a cohort (group of same-aged individuals) in a pop. from birth to death
    ★ Faster drop in line = quicker die-off of individuals
    ★ Slower drop in line = longer avg. lifespan

Type I (mostly K-selected)

  • High survivorship early in life due to high parental care
  • High survivorship in mid life due to large size & defensive behavior
  • Rapid decrease in survivorship in late life as old age sets in
    • Ex: most mammals

Type II (in between r & K)

  • Steadily decreasing survivorship throughout life

Type III (mostly r-selected)

  • High mortality (low survivorship) early in life due to little to no parental care
  • Few make it to midlife; slow, steady decline in survivorship in mid life
  • Even fewer make it to adulthood; slow decline in survivorship in old age
    • Ex: insects, fish, plants

Invasive Species

Objective/EKs/Skills

  • LEARNING OBJECTIVE EIN-4.A
    • Explain the environmental problems associated with invasive species and strategies to control them.
    • ESSENTIAL KNOWLEDGE EIN-4.A.1
    • Invasive species are species that can live, and sometimes thrive, outside of their normal habitat. Invasive species can sometimes be beneficial, but they are considered invasive when they threaten native species.
    • ESSENTIAL KNOWLEDGE EIN-4.A.2
    • Invasive species are often generalist, r-selected species and therefore may outcompete native species for resources.
    • ESSENTIAL KNOWLEDGE EIN-4.A.3
    • Invasive species can be controlled through a variety of human interventions.

Invasive Species Basics

  • Species not native to an area, introduced often by human transport
  • R-selected, generalists
  • R-selected and generalist species are more likely to be invasive
    • No natural predators to control pop.
    • High biotic potential & low parental care
    • Diverse habitat & food needs
    • Highly adaptable
  • Highly competitive (aggressive feeders or fast growers) for resources
  • Can thrive in their non-native habitats

Invasive Species to Know

  • Zebra Mussel
    • Aggressive filter feeders, eating algae many other species rely on
    • Clog intake pipes
    • 1 mil. eggs/yr.
    • Transported by ship ballast water
  • Kudzu Vine
    • Planted to limit soil erosion in southern US
    • Grows very rapidly
    • Outcompetes natives for sunlight; growing over them
    • No herbivore control in US
  • Asian Carp
    • Brought in to control algae growth in aquatic farms
    • Escaped to Mississippi river; outcompete native fish for food and space
    • Decreases fishery production & value
  • Pythons (FL)
    • Brought to Florida as pets, released into wild by owners
    • Decimated mammal populations in Everglades ~90-95%
    • Aggressive hunters with no natural predators
  • Emerald Ash Borer
    • Larvae laid in bark, eat their way into phloem
    • Spread by wood packing materials of ships/planes & fire wood
    • Disrupts tree nutrient transport, killing them
  • Cane Toad
    • Introduced to eat cane beetles causing sugarcane crop loss in Australia
    • Became invasive due to huge appetite
    • Expanding range due to global warming
    • Drove declines in other amphibians and small reptiles

Controlling Invasives

  • Invasives estimated to cost US 120 billion/year (2005 est.)
    • Lost ag. productivity, tourism, property value decline, fishery decline, control and removal costs
  • Control/Removal Methods
    • Laws preventing transport of invasives (firewood for emerald ash borer)
    • Removal of hosts (dead ash trees for EAB) to reduce spread
    • Introduction of natural predator (biological control)
    • Chinese wasps to kill emerald ash borer
    • Careful boat cleaning & inspection (zebra mussels)
    • Physical removal (hunting pythons, detaching z. mussels, pulling plants out, cutting trees down)

Endangered Species

Objective/EKs/Skill

  • LEARNING OBJECTIVE EIN-4.B
    • Explain how species become endangered and strategies to combat the problem.
    • ESSENTIAL KNOWLEDGE EIN-4.B.1
    • A variety of factors can lead to a species becoming threatened with extinction, such as being extensively hunted, having limited diet, being outcompeted by invasive species, or having specific and limited habitat requirements.
    • ESSENTIAL KNOWLEDGE EIN-4.B.2
    • Not all species will be in danger of extinction when exposed to the same changes in their ecosystem. Species that are able to adapt to changes in their environment or that are able to move to a new environment are less likely to face extinction.
    • ESSENTIAL KNOWLEDGE EIN-4.B.3
    • Selective pressures are any factors that change the behaviors and fitness of organisms within an environment.
    • ESSENTIAL KNOWLEDGE EIN-4.B.4
    • Species in a given ecosystem compete for resources like territory, food, mates, and habitat, and this competition may lead to endangerment or extinction.
    • ESSENTIAL KNOWLEDGE EIN-4.B.5
    • Strategies to protect animal populations include criminalizing poaching, protecting animal habitats, and legislation.

How Species Become Endangered

  • Poaching
    • Poachers hunt exotic species for fur, tusks, horns
    • May also be over harvested or hunted for food
    • Removed from wild & sold as pets
  • Special food/habitat needs
    • Niche specialists are more prone to endangerment due to specific food/habitat needs
  • Invasives
    • Invasives can outcompete natives for resources (food, water, sun, space)
    • Zebra mussels have endangered 30 native mussel species in US rivers
  • Climate Change
    • Less tolerant of changing climate, habitat loss, wildfires, deforestation, urbanization, etc.
    • Shifts habitats of many species
    • Migration to new habitat is harder with fragmentation/loss
    • Changes in temp/precip. can occur too rapidly for some species to migrate or adapt

Endangerment by Taxon

  • 41% Amphibians
    • Especially vulnerable to climate change due to biphasic life (relying on water and land) and highly permeable skin
  • 25% Mammals
  • 13% Birds
  • 33% Warm Water Coral
    • Threatened by changing ocean temperature and pH (ocean acidification from increasing atm. CO_2 levels)
  • 34% Conifers
    • Coniferous forests sequester 3X as much CO_2 as temperate or tropical forests
    • Threatened by disease and warming temperatures expanding insect pest ranges

Specialists vs. Generalists

  • Specialists
    • Less likely to move to new habitat
    • Less likely to adapt to new conditions
    • Disadvantaged by rapidly changing habitat conditions
    • Most likely to be endangered or become extinct
  • Generalists
    • More likely to move to new habitat
    • More likely to adapt to new conditions
    • Advantaged by rapidly changing habitat conditions
    • Least likely to be endangered or become extinct

Competition & Endangerment

  • Interspecific competition: competition for resources (food, nest sites, water) amongst members of different species
    • Can cause species to become threatened, especially when combined with general habitat fragmentation or loss due to human land use
    • Can further threaten species already vulnerable to habitat disruption due to climate change

Protecting Endangered Species

  • Protect Wildlife Habitats
    • Designating areas with important habitats as:
    • National parks
    • Wildlife preserves
    • Animal sanctuaries
    • Prevention of:
    • Hunting, development, fragmentation, deforestation
    • Allows species to breed and reestablish population size
  • Poaching Prevention
    • Hiring of armed guards to monitor populations and prevent poaching
  • Legislation
    • Laws that punish poaching severely, with stiff fines or jail time
    • CITES: International agreement for countries to set up agencies to monitor import and export of endangered species (as specified by IUCN Red List)
    • Endangered Species Act: US law giving USFWS power to designate species as endangered or threatened, monitor trade, and purchase land critical to these species’ habitats

Carrying Capacity

LEARNING OBJECTIVE ERT-3.D

  • Describe carrying capacity.
    • ESSENTIAL KNOWLEDGE ERT-3.D.1
    • When a population exceeds its carrying capacity (carrying capacity can be denoted as K), overshoot occurs. There are environmental impacts of population overshoot, including resource depletion.
  • LEARNING OBJECTIVE ERT-3.E
    • Describe the impact of carrying capacity on ecosystems.
    • ESSENTIAL KNOWLEDGE ERT-3.E.1
    • A major ecological effect of population overshoot is dieback of the population (often severe to catastrophic) because the lack of available resources leads to famine, disease, and/or conflict.

Carrying Capacity (k):

  • The max. Number of individuals in a pop. that an ecosystem can support (based on limiting resources)
    ★ Fig. 1 is theoretical
    ★ Fig. 2 is more realistic
    ★ Pop. briefly “overshoots” (k) and then die-off happens

Carrying Capacity (k)

  • Highest pop. size an ecosystem can support based on limiting resources:
    • Food
    • Water
    • Habitat (nesting sites, space)
  • Overshoot: when a population briefly exceeds carrying capacity
    • Ex: deer breed in fall, give birth all at once in spring; sudden spike in pop. = overshoot
  • Consequence of overshoot: resource depletion ex: overgrazing in deer
  • Die-off: sharp decrease in pop. size when resource depletion (overshoot) leads to many individuals dying
    • Ex: many deer starve with too many new fawns feeding in spring

Die-off Example

  • Reindeer of St. Paul Island
    • 25 introduced in 1910
    • Growth was gradual (10’-30’), then exponential (30’-37’)
    • Carrying capacity was overshot
    • Sharp die-off lead to pop. crash as food resource (lichen) were severely depleted
  • Real pops. don’t always fluctuate around carrying capacity. If resource depletion is severe enough, total pop. crash can occur

Predator-Prey Interactions & Trophic Cascade

  • Food webs show how increase or decreases in population size of a given species impact the rest of the food web
    • Ex: Increase in python population
    • Decrease in frog & rat populations
    • Increase in grasshopper population
    • Decrease in corn
  • Trophic cascade: removal or addition of a top predator has a ripple effect down through lower trophic levels
    • Ex: decline in wolf pop. = increase in deer population which leads to overgrazing & decline in trees

Pop. Growth & Resource Availability

LEARNING OBJECTIVE ERT-3.F

  • Explain how resource availability affects population growth.
    • ESSENTIAL KNOWLEDGE ERT-3.F.1
    • Population growth is limited by environmental factors, especially by the available resources and space.
    • ESSENTIAL KNOWLEDGE ERT-3.F.2
    • Resource availability and the total resource base are limited and finite over all scales of time.
    • ESSENTIAL KNOWLEDGE ERT-3.F.3
    • When the resources needed by a population for growth are abundant, population growth usually accelerates.
    • ESSENTIAL KNOWLEDGE ERT-3.F.4
    • When the resource base of a population shrinks, the increased potential for unequal distribution of resources will ultimately result in increased mortality, decreased fecundity, or both, resulting in population growth declining to, or below, carrying capacity.

Pop. Characteristics

  • Size (N): total # of individuals in a given area at a given time
    • Larger = safer from pop. decline
  • Density: # of individuals/area
    • Ex: (12 panthers/km2)
    • High density = higher competition, possibility for disease outbreak, possibility of depleting food source
  • Distribution: how individuals in pop. are spaced out compared to each other
    • Random (trees)
    • Uniform (territorial animals)
    • Clumped (herd/group animals)

Pop. Characteristics & Growth Factors

  • Sex Ratio: ratio of males to females. Closer to 50:50, the more ideal for breeding (usually)
    • Die-off or bottleneck effect can lead to skewed sex ratio (not enough females) limiting pop. growth
  • Density-Dependent Factors: factors that influence pop. growth based on size:
    • Ex: food, competition for habitat, water, light, even disease
    • All of these things limit pop. growth based on their size; aka - small pop. don’t experience these, large do
  • Density-Independent Factors: factors that influence pop. growth independent of their size
    • Ex: natural disasters (flood, hurricane, tornado, fire)
    • It doesn’t matter how big or small a pop. is, natural disasters limit them both

Biotic Potential

  • Max. potential growth rate, with no limiting resources
    • May occur initially, but limiting resources (competition, food, disease, predators) slow growth, & eventually limit pop. to carrying capacity (k)

Calculating Population Change

  • Population Size = (Immigrations + births) - (emigrations + deaths)
    • Ex: An elk pop. of 52 elk has 19 births and 6 deaths in a season, and 5 new elk immigrate to the herd and 0 elk emigrate from the heart

Ecological Tolerance

LEARNING OBJECTIVE ERT-2.F

  • Describe ecological tolerance.
    • ESSENTIAL KNOWLEDGE ERT-2.F.1
    • Ecological tolerance refers to the range of conditions, such as temperature, salinity, flow rate, and sunlight that an organism can endure before injury or death results.