Studied by 12 people
Stimulus
An external signal that causes a response in an organism
What do organisms respond to their environment with?
Their behaviors and physiology
Tropism
Growth toward or away from a stimulus.
For example, sunlight is a stimulus that creates a positive tropism in plants, as they grow toward it.
Is a tropism only in plants
No, it’s also displayed in viruses, pathogens and other biological organisms
Taxis
A directed behavior toward or away from a stimulus.
The planaria will move away from light, displaying a negative taxis.
Phototropism and Phototaxis
When light is the stimulus
Kinesis
Random movement; not based on stimuli
When is kinesis usually considered?
In animals and other organisms capable of random movement
Communication
An external or internal signal may cause communication behaviors between organisms, which may benefit the survival and reproductive success of a group of organisms.
Communication Methods
List
Visual
Tactile
Audible
Electrical Signals
Chemical Signals
Communication Uses
List
Indicate Dominance
Find Food
Establish Territory
Ensure Reproductive Success
Aposematic Coloration
In animals, it communicates to other species that an individual tastes bad or is poisonous
Chemical Signals
Many animals have scent glands they use to mark their territory, or they use their urine, feces, etc.
These are also used to communicate social status and warn competitors.
Attracting Mates
Chemical signals - Communication
Females are attracted by pheromones
Cooperation
Behaviors that involve teamwork between individuals of the same species
What does cooperation do?
Increases fitness of individuals and survival of the population
Example of cooperation
Fish
Schooling
more intimidating to predators
It may also save energy due to less drag
Example of cooperation
Bees
Bees use a dance to tell other bees where to collect pollen and nectar
Builders: provides home for individuals and the colony
Heater Bees: Maintains the temperature of the colony and larva during colder months
Worker Bees: collect pollen for queen and larva.
Queen Bee: egg laying habits may be altered depending on the pollen that is collected
Response and Communication
Effects on natural selection and evolution
Natural selection favors innate and learned behaviors that increase reproductive success and survival
Innate Behavior
Genetically controlled and happen without prior knowledge or experience
Ex: all newly born mammals instinctively begin to suckle after being born.
Learned Behavior
Developed as a result of an experience
Example: Very young ducks and geese are frightened of any shadow that moves overhead. Within a few days of hatching, the young birds find that some shadow moving overhead mean nothing. They soon habituate to these shadows and no longer try to escape from them.
Energy
Organisms use energy to grow, keep homeostasis, and reproduce
Endothermic Organisms
Maintain a constant body temperature by using thermal energy from their metabolic processes
Ex: mammals shiver to keep warm, use heat of metabolism
Endothermic organisms examples
Mammals, birds, dinosaurs, dolphins, warm-blooded animals
Relationship between the size of an organism and its metabolic rate
Usually inverse, like in mammals.
The smaller the size of the mammal, the higher the metabolic rate. (Remember SA to volume ratio!)
SA to volume Ratio
The amount of surface area or total exposed area of a body relative to its volume or size
Surface area/volume
Ectothermic Organisms
Do not have the ability to internally regulate their body temperature
They must alter their behavior to change their body temperature.
Ex: They can group together with other animals(snakes congregating), and crawl into the sun.
Ectothermic organisms examples
Snakes, crocodiles, insects, amphibians, fish, turtles, reptiles, cold-blooded animals
What are ectothermic organisms susceptible to?
Ambient temperature
What type of organism has the greatest metabolic rate? The lowest? What’s the last type (middle)?
Greatest: Endotherms
Lowest: Unicellular Organisms
Middle: Ectotherms
Do all organisms have the same reproductive strategies?
No, organisms have different reproductive strategies in response to energy availability
r-selected species
Many offspring
A small investment from the parent
Don’t really raise their young with care, they just increase population size rapidly
Where are r-selected species common?
In areas where the environment changes more frequently and resources are scarce
K-selected species
Few Offspring
More investment from the parent
Care is given to each offspring
What environment are K-related species common?
Stable environments
It’s energy efficient
Which species fluctuates around the carrying capacity?
r-selected or K-selected
K-selected species
Reproduction rates of
Oyster
Fish(Tuna)
Frog
Hare
Large Cat(Puma)
Chimpanzee
From top to bottom, what does it represent?
Oyster = 5 million per year
Fish(Tuna) = 6,000 a year
Frog = 200 a year
Hare = 12 a year
Large Cat(Puma) = 2 a year
Chimpanzee = 1 every 5 years
Top to bottom = scale from r to K-selected species
Seasonal reproduction…
occurs at different times of the year in plants and animals
Examples of seasonal reproduction
Plants produce pollen for sexual reproduction during the seasons when pollinators are most active.
Animals reproduce in the spring and summer when food is most plentiful.
Grizzly bears mate in May and July, but the female delays implantation of the fertilized egg until October or November if food is plentiful. If food is scarce, the fertilized egg is reabsorbed.
Reproduction is triggered by a critical photoperiod (a relative length of night and daytime)
Trophic Structures
What is it determined by?
The trophic structure of a community is determined by the feeding relationships between organisms
Trophic Levels
The positions away from the primary energy source in an ecosystem which is the sun
links in the trophic structure
Food Chain
The transfer of food energy from plants → herbivores → carnivores → decomposers
Autotrophs
Make their own organic compounds for energy through
What are the types of autotrophs, what do they do and what’s an example?
Photoautotrophs
Photosynthesis (uses sun energy)
Makes inorganics to organics
Plants & photosynthetic organisms
Chemoautotrophs
Chemosynthesis (uses chemical energy)
Animals living by hydrothermal vents
Heterotrophs
Must obtain their organics from another source (they consume their food).
They metabolize carbs, lipids, and proteins through hydrolysis for energy
Length-Limiting Factor
of a food chain
Inefficiency of energy transfer along chain - usually a food chain is only 10%(on average) efficient.
What length of food chains are the most stable?
Short food chains
Food Chain Base Structure
primary producer → primary consumer → secondary consumer → tertiary consumer → quaternary consumers
Marine Food Chain
Basic
phytoplankton → zooplankton → carnivore → carnivore → carnivore
Terrestrial Food Chain
Basic
plant → herbivore → carnivore → carnivore → carnivore
What do the arrows in a food chain/web represent?
Energy transfer
In a food chain what is energy lost as? How much of the energy is lost in what terms?
Energy is lost as heat
90% is lost in terms of calories
Are there more top predators or producers & primary consumers on average in an ecosystem?
More producers & primary consumers
Food Web
Two or more food chains linked together
Can a given species weave into the web at more than one trophic level?
Yes
Pyramid of Energy
Lower levels weigh more, this is known as biomass (stored energy)
The number of individuals = higher, lower on the pyramid
Energy decreases as you move further up the pyramid
What tends to be true about energy pyramids?
The bottom must support the top; it doesn’t usually go past quaternary consumers
Population
A group of individuals of the same species living in the same area
Population interactions
They interact with one another in complex ways
They typically breed with one another more frequently than they do with those from other populations
What are adaptations in an organism related to?
Adaptations in organisms are related to obtaining and using energy in a particular environment
What does population size depend on?
A number of factors?
Food availability
Energy availability
Food availability
Population size
More Food: larger population size, higher reproduction rate, and survival rates of offspring increase.
Less Food: smaller population size, lower reproduction rate, and survival rates of offspring decrease
Energy availability
Population size
When energy availability in the environment changes, organisms have different adaptations
Ex: fat storing in winter months, losing leaves when day length changes, migration
Population Growth Formula
What does each part mean?
dN = change in population size
dt = change in time
B = birth rate
D = death rate
Exponential Growth
When does it occur, what does it mean, what shape is it represented by
This type of growth occurs when a population grows at a constant rate when resources are abundant
This means that the number of organisms added to the population each generation INCREASES as the population grows in size.
The time it takes to produce offspring status is the same (often assumed to be 1 year...unless you are told otherwise)
Represented in a J curve
Exponential Growth Formula
What does each part mean?
dN/dt = r(max = subscript)N
dN = change in population size
dt = change in time
N = population size
rmax = maximum per capital growth rate of population = r
Population Density
Refers to how close individuals within a population live to one another
Food availability
Population density + what does it mean
A high abundance of food often results in a high population density,
This can mean a higher reproductive rate and limited space
When food is limited, population density may decrease
This can mean lower reproductive rates and individuals are more spread out from one another
What cab population size be influenced by?
Factors
Density-dependent Limiting Factors OR Density-independent Limiting Factors
Density-dependent Limiting Factors + examples
Abiotic (non-living) or biotic (living) factors that can limit a population’s size based on its density
Examples: Competition for food or territory, predators, nutrient availability, parasites
Density-independent Limiting Factors + examples
Abiotic (non-living) or biotic (living) factors that can limit a population’s size regardless of its density
Examples: natural disasters like floods, forest fires, volcanic eruptions, human causes (pollution)
Predator-Prey Relationships
Predator numbers have a generational lag time, and their populations will peak slightly after prey number peaks
Density-dependent
In a graph, after the peaks, the numbers will fluctuate around the carrying capacity
Logistic Growth Model
What does it describe and what shape is it represented by
Describes the population growth model that begins with slow growth, immediately followed by exponential growth, and then ends with stable maximum growth that levels off
Shown in an S curve
Starts as a J curve until carrying capacity → population growth lowers
Carrying Capacity
Maximum number of individuals an environment can sustain
Can populations exceed the carrying capacity?
Yes, under certain conditions, populations can exceed the size of the carrying capacity and then return to normal and fluctuate around the carrying capacity
Logistic Growth Model Formula
What does each part mean?
dN/dt = r(max = subscript)N(K - N/K)
dN = change in population size
dt = change in time
N = population size
K = carrying capacity
rmax = maximum per capital growth rate of population = r
Community
Refers to a group of different species living together in the same location and interacting with one another; biotic factors
What are communities described based on?
Species diversity and species composition
Species Diversity
Refers to the variety of species and the quantity of individuals included in a species within a given community
Increased diversity = what?
In terms of en ecosystem
Stability
For example, an ocean community consists of one species of sea turtle, yet there are 15 sharks and 62 sea turtles
Which is most diverse?
Community 1: 90A, 10B, 0C, 0D
Community 2: 25A, 25B, 25C, 25D
Community 3: 80A, 5B, 5C, 10D
Community 2
Community 1: 90A, 10B, 0C, 0D; NOT CORRECT = Only 2 species
Community 2: 25A, 25B, 25C, 25D; CORRECT = 4 species in large quantities
Community 3: 80A, 5B, 5C, 10D; NOT CORRECT = Small quantities of species
In a community, if one species gets wiped out, there should still be ______ from the _________ of species
In a community, if one species gets wiped out, there should still be stability from the diversity of species
Species Composition
Refers to the identity of each species in the community
For example, an ocean consists of Pomacanthus paru and Pomacanthus xanthometopon; two species of angelfish
Simpson’s Diversity Index
An equation used to measure species diversity(biodiversity of a habitat)
The higher the index value, the more diverse the community
Based on random samples of the environment
Simpson’s Diversity Index Formula
What does each piece mean?
What does a value of 1 mean?
Diversity Index = ∑(n/N)²
n = total number of organisms of a particular species
N = total number of organisms of all species
Closer to 1 = more diversity
What do interactions among populations determine?
How they access energy and matter
Do communities change over time depending on interactions between populations
Yes
Competition
An interaction that can affect how populations access energy and matter
Can result in a change in community structure
Can occur within or between species
Competition for food and habitats
Interactions between species can be…
positive, negative or neutral
Symbiotic Relationships
A close, prolonged association between two or more different biological species
Mutualism
Commensalism
Parasitism
Positive Species Interactions
Mutualism: both species benefit (+/+)
Commensalism: one species benefits but the other is not harmed nor helped (+/o)
Negative Species Interactions
Predator-Prey: one species uses the other as a food source (+/-)
Parasitism: one species benefits at the harm of another (+/-)
Neutral Species Interactions
Have no impact on the species involved
Example, deer and rabbits living in a forest (o/o)
Bracket or shelf fungi as tree parasites
They produce fruiting bodies that grow on the bark of the tree
They absorb nutrients from the outer bark of the tree
Can cause weakening of the external structure of the three
Reduced canopy and foliage density
Frees up resources
Can infect the interior parts of the tree
Branches of entire tree may rot and fall
Provides new available niches and habitats
They provide microhabitats for insects and other organisms
Insects can live in the holes the fungi make in the tree bark
They provide a food source for insects and other organisms
Some insects use the fungi as a food source
Niche Partitioning
Refers to a decrease in competition over limited resources between two similar species because each species is accessing the resource in different ways
Niche
Everything that an organism does; it’s job
Can organisms occupy the same niche?
Nope, no two species have the same niche; they may be close but they tend be at least slightly different in a well established ecosystem
What can disruption cause in a food chain?
A negative cascade of effects
Trophic Cascade
Refers to the negative effect the removal of or decrease in a key species has on other trophic levels
What can a population experience with the removal of a key species? What results from this?
Populations can experience exponential growth or death with the removal of a key species
Results in the interruption of the flow of energy through the ecosystem and resource availability
Note 
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