Lecture 9 + 10 Flashcards
Competition between individuals of the same species is which type of competition?
Intraspecific competition
A single algal species competes for a required resource, silicate. As the number of individuals increases, there is less silicate available for the original individuals. This is an example of:
Exploitation (competition)
Snowy plovers, a coastal bird species, are found to live only on sandy beaches. Where snowy plovers live is referred to as their:
Habitat
Competition between individuals of the same species can have effects on their
- survival
- growth
- reproduction
- access to mates
For any given species, there is a _______, which describes the niche that occurs under normal circumstances of interspecific competition within a community and typically differs from the hypothetical ______, which describes the niche that the species would inhabit if interspecific competition was removed.
realized niche, fundamental niche
The Competitive Exclusion Principle states that
If two competing species coexist in a stable environment, then they do so as a result of niche differentiation
Six types of species interactions
- amensalism
- commensalism
- competition
- exploitation
- mutualism
- neutralism
The six types of species interactions are based on how 2 species influence each other’s fitness
A negative, positive, or no effect on another species.
Example of exploitation
+/-
A spider eats a fly
Example of competition
-/-
A sparrow and a cardinal eat the same seeds
Example of mutualism
+/+
A butterfly and a flower
Example of neutralism
0/0
Two species that don’t influence each other
Example of commensalism
+/0
A vulture eats the scraps of a lion’s kill
Fungi on dead trees
Example of amensalism
-/0
A flower is stepped on by an elephant
Frog calls affecting an owl’s ability to hear prey/mice
Competition
Can be for any limited resource (ex. mates, locations, food, etc.)
It is a -/- interaction, it is not like sports
- there are costs to competition energetic expenditure, time, risk of injury, etc.
Pizza arrives at a party and those individuals who randomly smell and find the pizza first will get the pizza and some people will go hungry. What type of competition is this?
Intraspecific competition and exploitation competition
- however, not technically a species interaction
- not the same as an +/- exploitation interaction; this is a form of competition based on exploiting resources
At a pizza party, you drop your pizza but a cute dog prevents you from getting the pizza. What type of competition is this?
Interspecific competition
Interference competition
At a party, someone else flirts with your potential mate. What kind of competition is this?
Intraspecific competition
Interference competition
Intraspecific competition
Occurs among individuals of the same species
Interspecific competition
Occurs between individuals of different species
Exploitative competition (resource or scramble competition)
Competition between individuals by reducing availability of shared resources
Interference competition (contest competition)
Direct competition between individuals for scarce resources by one impeding or denying access to the resource by another
Competition
As population size increases intraspecific competition typically becomes greater.
This also applies to interspecific competition (the -/- interaction). If there are many individuals of a competitor species around, it can reduce fitness.
Competition over resources
Resource utilization curves
ex. small ground finches eat small seeds, medium eat medium seeds, large eat large seeds. Three different resource curves: seed depth (mm) x diet proportions
No competition curves
2 curves don’t touch, side by side
Low competition curves
2 curves overlap a little
Medium competition
2 curves overlap more
High Competition
2 curves almost overlap completely
Competitive exclusion
When 2 species are very similar, they may not be able to coexist because competition is so strong.
One species may consume all the resources leaving little for the other.
If 1 species is a poor competitor, it can go locally extinct.
If 2 species are very similar, one may randomly go locally extinct.
Gause’s experiments
Both species of single-celled organisms thrived when grown individually.
Highlights exploitative competition – P. aurelia outcompeted P. caudatum for resources
However, Gause found that by tweaking environmental factors like type of food, he could create conditions where the two organisms co-habited.
-> led to competitive exclusion principle
Bar graph to show average fitness when species are separate (two different sizes of gerbils)
Individual fitness around the same, medium height
Bar graph to show average fitness when species are together (two different sizes of gerbils)
Smaller species fitness is low, bigger species fitness is high
-> competition can be relatively symmetric or asymmetric
With the gerbils, why is this the pattern we find?
Larger species has a strong negative impact on smaller ones because larger ones are a dominant competitor (dominant interference competitor).
The competition is asymmetric.
The larger species are not “good for” smaller ones. Competition reduces fitness.
Fitness when species are together
While larger species has higher fitness, it is still lower than individual fitness when the species are separate.
If we put both larger and smaller species together in a 100x100m area in the desert. What will happen after 50 years?
The two species of gerbils would coexist.
How can the two species of gerbils coexist? Why don’t the larger ones drive the smaller ones extinct like the 2 species in the paramecium example?
Time has been insufficient to allow exclusion
There is immigration
The environment is temporally variable
The environment has spatial variation
There are multiple “resources”
-> maybe the smaller gerbils are better at harvesting seeds at low density
Resource use when small and large gerbils are together
Small gerbils: upside down parabola, specializing in lower patch seed density
Large gerbils: upside down parabola, top part almost flattens out, trailing down, better at higher patch seed densities
Patch seed density v. proportion use
To coexist with other species, a species needs to be the best at:
Something, sometime, somewhere, somehow, etc.
- they need their own niche
The niche concept
The range of environmental conditions and resources within which individuals of a species survive, grow, and reproduce.
Resource utilization curves
Resource gradient v. intensity of resource utilization
Both bell curves, width is niche breadth, the overlap between the two curves is called the niche overlap.
The distance between the max of bell curve is called the niche separation.
-> narrow niche breadth = specialist
-> wide nich breadth = generalist
The idea of niche dimensions
One dimension (ex. temperature) is one parallel line.
Two dimension (ex. temperature and humidity) is a rectangle. Temp on x axis, precipitation on y axis
Three dimensions (ex. temperature, humidity, and soil grade) is a cube. Soil grade axis goes out like a cube.
Which scenario is most plausible?
- a penguin lives in the rainforest
- a white-tailed deer lives in the desert
- a lion lives in the tundra
- a clownfish lives in fresh water
None of the above!
The niche as an n-dimensional hypervolume
The concept of the niche based on a species tolerance and use of a series of n environmental factors and resources.
Can define multiple (n) biotic and abiotic resource axes, each utilized with a certain frequency distribution.
Fundamental niche
The full hypervolume or range of environmental factors permitting a species to survive and reproduce (think abiotic)
Graph on curve is half a bell curve flattening out at the top
Realized niche
The conditions under which an organism actually exists, after limitations by factors such as competition, disease, and predators (think biotic)
Graph is a bell curve
Fundamental vs. realized niche
The realized niche is smaller than the fundamental niche
Can be smaller on numerous “n” dimensions
What might happen when 2 similar species end up together that permits coexistence over the short term?
What might happen when 2 similar species end up together, that permits coexistence over evolutionary time?
Resource partitioning is a behaviour that might allow for co-existence
- it is possible for a species to start concentrating on the lower end of the resource gradient and the other on the higher end
-> less overlap and can co-exist
Character displacement (evolutionary time)
ex. beak size influences the sizes of the seeds the birds can eat
- beak sizes of two species differ considerably where they both live
- however, when the two species live apart on different islands, they have similar beak sizes
Competition can be context dependent
Sometimes one species is the dominant competitor in one environment and the other species are the dominant competitor in another environment.
ex. in the wet, one species of beetle dominates and in the dry, the other dominates
-> so the interactions between two species can be context dependent
Can 2 species that are very different from each other be engaged in competition?
Yes, the limited resource is what matters.
Competition between dissimilar species?
Ants and rodents -> guilds
Both compete over seeds
They have high levels of overlap in their resource distribution curves.
Although note here are these really, really small seeds the rodents can’t even handle, but the ants can.
That being said, two very different species in very strong competition because they are utilizing the same limited resource.
Guilds
A way that we define groups of organisms that use similar resources
Interaction: A gopher digs a hole in a patch of grass
Amensalism
Interaction: A cow eats grass
Exploitation
Interaction: A beaver makes a dam which creates habitat for a species of fish
Commensalism
Interaction: A hummingbird pollinates a flower while it ingests nectar
Mutualism
Interaction: A raccoon and a crow fight over some edible garbage
Competition
Interaction: A sparrow and a squirrel forage for different foods in the same forest but do not interact or affect one another
Neutralism
The breeding sites of Virginia’s warbler and orange-crowned warblers overlap in central Arizona. When one species was experimentally removed, the remaining species fledged greater percentages of young per nest. The experimental removal of one species indicates that
- There is intraspecific competition
- There is differential resource utilization
- There is interspecific competition
- The two species occupy different niches
There is interspecific competition
True or false: All else being equal, species that have a greater overlap in resource utilization curves are more likely to be stronger competitors than species that have little overlap in resource utilization curves.
True
What does the Competitive Exclusion Principle state?
- The Competitive Exclusion Principle states that if two competing species coexist in a stable environment, then they do so as a result of differentiation of their realized niches.
- The Competitive Exclusion Principle states that all species within a community coexist in an unstable environment, and that they are structured by competition that leads to realized niches.
- The Competitive Exclusion Principle states that if a guild of competing species coexist in an stable environment, they do so as a result of differentiation of their fundamental niche.
- None of the above
The Competitive Exclusion Principle states that if two competing species coexist in a stable environment, then they do so as a result of differentiation of their realized niches.
You determine that two species of birds coexist in the same tree, but that they have different feeding behaviors that prevents them from competing with one another for resources. One bird species feeds on insects found in the bark of this tree, while the other bird species feeds on insects at the branch tips. One explanation of your observation could be that:
- Coexistence is due to niche differentiation
- Coexistence is due to shared resource utilization
- Coexistence is not due to resource specialization
- None of the above
Coexistence is due to niche differentiation
In a two-species interaction, one species is a better competitor than the other. The weaker competitor may be able to persist if
It is better at something some time, somewhere, or somehow
Which of the following is true?
- A realized niche is typically smaller than a fundamental niche
- A fundamental niche is typically smaller than a realized niche
- The fundamental and realized niches are typically about the same size
- The niche concept is complex. It is not reasonable to make a generalization concerning the relationship between realized and fundamental niches
A realized niche is typically smaller than a fundamental niche.
When we think of a fundamental niche it typically involves abiotic components of the environment. For example the proper temperature and moisture combinations for an organism. When we think of the realized niche we consider more biotic components. Even if the temperature and moisture combinations are perfect for an organism other organisms such as competitors might limit the ability of a species to live in a location.
A niche for a species of salamander is determined by the density of individuals in the area, soil temperature, amounts of precipitation, and food availability. Thus, the niche would be modeled as a:
A four-dimensional niche volume
There is a species of sparrow in the forest. One day a new species of sparrow is introduced from another continent. Both species eat nearly the same size of seeds. Which of the following are possible outcomes of their interaction?
- Character displacement results in the sparrows eating slightly different sizes of seeds and the species coexist
- Resource partitioning results in the sparrows eating slightly different sizes of seeds and the species coexist
- Competitive exclusion results in one species driving the other locally extinct
All answers are possible. Resource partitioning could occur in ecological time or character displacement could occur in evolutionary time. It is also possible that competitive exclusion occurs. There are also many possibilities in addition to this. For example the environment might be heterogeneous enough to permit coexistence, or the 2 species could differ on another niche axis.
Which type of organism attacks their prey, kills it, and then consumes it?
True predator
Which type of organism typically does not kill their prey, but consumes part of each prey item, and does not need a host?
Grazer
What type of organism relies on a host, but it does not usually kill it?
Parasite
A spider that spins a web to capture prey would be considered which of the following?
- a foraging predator
- a sit-and-wait predator
- a grazer
- a parasitoid
A sit-and-wait predator
Mistletoe is a plant that grows on other plants and is best categorized as a
Parasite
If a plant produces chemical defences in response to grazers this could be called
An induced response
Exploitation interactions include
Grazing, parasitism, and predation
Predator
Any organism that consumes all or part of another living organism (its prey or host) thereby benefiting itself, but reducing the growth, fecundity, or survival of the prey
True predators
- Invariably kill their prey and do so more or less immediately after attacking them
- Consume several or many prey in the course of their life
Grazers
- “Attack” several/many prey in the course of their life
- Consume only part of each prey item
- Do not usually kill their prey, especially in the short term
-> cows eat grass (a living organism), so are predators (as well as grazers, a sub-class of predators) by this definition
-> not really true though, cows aren’t really predators…
Zebras and cows are grazers
Zooplankton feeding on phytoplankton or bacteria
-> but this does not fit the text’s definition, since the entire phytoplankton or bacterial cell is consumed and is killed
Is the fitness of the population being exploited always reduced by the exploitation?
No
ex. “Field gentian” plant compensates for grazing, and may even benefit (it has evolved with grazing as a dominant factor)
Impact of predators on prey population
- Predators often have little impact on prey populations as a whole because of the particular individuals they attack
- Many large carnivores, for example, concentrate their attacks on the old (and infirm), on the young (and naive), or on the sick
- The young gazelles will have been making no present reproductive contribution to the population, and many would have died anyway from other causes
Impact of predators, grazers, and parasites on prey population
- Predation, grazing, and parasitism do not generally eliminate the population being consumed
- Rather, reduce the size of the population being consumed
- Can result in pronounced predator-prey cycles
Predator-prey cycles worked out (semi-independently) by
Lotka and Volterra in the 1920s and 1930s
- both were born in Europe
- Lotka was born a US citizen
- Lotka or Volterra never worked together
- Lotka was trained at Cornell
Predation, grazing, and parasitism do not occur in a vacuum
Rather, these interact with other ecological processes and considerations, including resource limitations and competition
Experiment with grasshoppers and predatory spiders, with and without fertilizer to increase grasshopper food supply
Only with large amounts of food (little competition) did removing predators allow more grasshoppers to survive
- no spiders, no fertilizer had a big drop, but ended up in similar spot
- only fertilizer, no spider had higher # of grasshoppers in the end compared to no spiders/no fertilizer, spiders/no fertilizer, and spiders/fertilizer
Some beneficial aspects of herbivory/grazing
In both grasslands and aquatic ecosystems, grazing of the photosynthetic organisms (grasses, algae) will recycle nutrients
This can stimulate further photosynthesis, leading to overall higher levels of production (if photosynthesis is limited by the rate of nutrient supply)
Exploitation (predation, grazing, parasitism) can influence community structure and biodiversity
When predation promotes the coexistence of species that might otherwise exclude one another, this is known as predator-mediated coexistence
Predation “defence” as a niche axis
Seed size in environment x fitness
No predator: one small bell curve on small end and one small on large end and one large overarching bell curve over everything
-> competitive exclusion
With predator: three equal sized bell curves, slightly overlapping
-> predator-mediated coexistence
The addition of the predator
Increases biodiversity
ex. Nine Scandinavian islands –pigmy owls occurred on only 4 of the islands. Five islands without the predatory owl were home to only one species, the coal tit.
In the presence of the owl (4 islands), the coal tit was always joined by 2 other tit species, the willow tit and the crested tit.
Some grazing can increase biodiversity, while more grazing may reduce it:
Number of plant species was greatest at intermediate levels of grazing by cattle in grasslands of Ethiopia.
Parasitism can also increase biodiversity
Parasitic plant “dodder (parasite on Salicornia, another plant) influences competition in California salt marshes, reversing competitive dominance.
What can an organism do in a world of high risk of being eaten to still have high fitness?
How do organisms reduce the risk of being eaten?
- Structural and physical defences
- Chemical mechanisms
- Behavioural mechanisms
Structural and physical defenses
Protective, camouflage
Induced defence
A defensive structure (or poison) that is produced in response to herbivory or predation
Behavioural avoidance –group advantage
Sentinels: many eyes, communication
Mobbing, defending (ex. ravens fighting off an eagle)
Intimidation by apparent “size” (ex. a school of fish)
Diel (day-night) migration of zooplankton up and down in the water column
Avoid predators during the day, their predators tend to be sight-dependent
- move to euphotic zone (0-100m) during the need to feed
- photosynthesize during the day, migrate to mesopelagic zone (100-1,000m)
Chemical defences
Bombardier beetle spraying noxious liquid
Hot peppers contain capsaicin, a toxin
Flesh of saddled toby is toxic if eaten (a type of fish)
Induced chemical defence
ex. Content of toxic pholorotannin increases in the brown macro-algae (“seaweed”) Ascophyllum nodosum when exposed to grazing snails (BUT not just to physical disturbance!)
- no response to momentary clipping or continuous clipping
-> somehow they know when it’s a snail eating them
Harmful algal blooms (HABs)
Large growth of micro-algae or cyanobacteria that produce toxins that can harm people, pets, livestock, and marine mammals through ingestion or contact with water, or consumption of shellfish that have concentrated the toxins.
- toxic “algae” are actually cyanobacteria
Often, warning colouration and pattern associated with chemical defences
- advertises danger to potential predators (opposite of camouflage)
- offers protection to the population, but of course not to the individual that is consumed
ex. saddled toby, monarch butterfly, venomous coral snake
What is happening to predators as prey evolve defences?
Evolutionary arms race
Other species copy the look of the toxic/venomous species to reduce danger from predators:
Mimicry
ex. venomous coral snake <-> non-venomous scarlet king snake
ex. monarch butterfly <-> viceroy butterfly (non-poisonous)
ex. saddled toby <-> filefish
Why don’t all organisms protect themselves to the hilt against being eaten at all times?
Spines/shells + chemical defences + camouflage + diel migration? Why not do it all?
Trade-offs with other necessities of life, such as growth and reproduction.
Life is full of trade-offs!
True or false: Predation and grazing typically have a negative impact on the fitness of the organism being consumed.
True – This is typically a +,- interaction. Where the organism that is being consumed has its fitness negatively impacted.
If a plant were grazed upon by individuals of a snail population, and the plant produced compounds to deter further feeding, then what might occur?
- The plant will remain similar and maintain its present biomass and growth rate
- The plant may experience a trade-off of some sort, because there is likely a cost to producing the compounds that deter grazers
- The plant will not experience any trade-offs since it is co-evolving with this grazing snail
- The snail will likely continue to graze because it is immune to the chemicals this plant produces
The plant may experience a trade-off of some sort, because there is likely a cost to producing the compounds that deter grazers
If prey are experimentally protected from predators then, all else being equal:
- Prey numbers typically decrease quickly
- Prey numbers may increase but then potentially decrease when resources become limiting
- Prey numbers usually do not change
- Prey numbers are not dependent on predators
Prey numbers may increase but then potentially decrease when resources become limiting
True or false: Predators can sometimes have little impact on prey populations
True. This can be true for several reasons. Predator populations may be low, prey populations may have high rates of growth, or predators may kill individuals that were not reproducing, or were likely to die of other causes (compensatory mortality)
True or false: Predators kill individuals, and therefore always tend to reduce biodiversity
False, concept of predator mediated coexistence
You have been studying a plant species for the last three years. On a trip to the Isle of Deerlessness you notice that the same plant species has a different leaf morphology compared to individuals on the mainland. Specifically, the island plants do not have sharp points around the perimeter of each leaf and are instead very smooth. You also learn that this island is devoid of deer, which specialize on this plant. Which hypothesis regarding the morphological differences between these plants is most reasonable?
-Leaves have evolved differently on the island because of climate
- Leaves have little need on the island for morphological defenses because their primary predator is not found there
- There is no way the two plants are the same species
- Specialized predators on the island ate the spikes off of these leaves
Leaves have little need on the island for morphological defences because their primary predator is not found there
Plants can produce chemical defences against herbivores:
- in response to herbivory
- to deter many different species of herbivores
- often at an energetic cost
- not necessarily in response to mechanical damage
True or false: Because exploitation interactions involve a +,- relationship, the + and the - balance each other out, such that exploitation interactions do not have ecosystem level impacts
False, the +/- do not “balance each other out”. Exploitation interactions can have large scale consequences.
Think of a scenario where wolves are introduced to an island where elk live. This elk population has not been in contact with wolves for thousands of years. Which of the following is most plausible:
- The carrying capacity and “r” of the elk population will increase
- There is an evolutionary arms race, where elk evolve defences as wolves continue to evolve to overcome those defences
- The wolf population will not persist more than a year because the elks are not accustomed to reacting to wolf predators
- Elk behaviour will not change in any way
- The survivorship of elk increases
There is an evolutionary arms race, where elk evolve defences as wolves continue to evolve to overcome those defences
