UNIT 4 - Chapter 1 - Interspecific Competition Flashcards
6 types of INTERSPECIFIC COMPETITION: a relationship that affects the populations of 2+ species adversely(-)(-), DUE TO species seeking a common resource in short supply. Same as intraspecific competition, but now it’s 2+ species.
There are two forms of this competition:
a) EXPLOITATION Competition: 2+ species compete for the same limited resources, do not interact directly, but using the resources still affects other species around them (Ex: one bird species is more efficient at finding insects, it may deplete the insects in that area, depriving food from the other bird species)
b)INTERFERENCE Competition: 2+ species do interact & directly interfere wth the other species access to resources (aggressive behaviour, making physical barriers)
TYPES:
- CONSUMPTION COMPETITION : when 1 species inhibits another species by consuming the shared resources (squirrels competing over acorns in an area)
- PRE-EMPTIVE COMPETITION : among sessile organisms (barnacles) where their occupation of an area precludes occupation from another species
- OVERGROWTH COMPETITION : one species grows over another species, with or even w/o physical contact, inhibiting access to a shared resource (a plant shades another plant by growing over it)
- CHEMICAL INTERACTION : chemical growth inhibitors or toxins released by a species inhibits another species from getting resources (called allelopathy : plants release a chemical which inhibit germination of another species)
- TERRITORIAL COMPETITION : behavioural exclusion, such as territorial defending, that literally prevents a species from entering an area.
- ENCOUNTER COMPETITION : when 2 species meet in a area by chance for a shared resource (when wolves meet at a dead carcass to feed off the one carcass together)
CHART BELOW:
* Species interact with each and it can be positive (+), negative (-), or neutral (0):
1. Neutral
2. Mutualism
3. Commensalism
4. Competition
5. Amensalism
6. Predation
7. Parasitism
8. Parasatodism
Why do these interactions matter?
Because it affects the probability dynamics for each species, including birth, death AND contribute to natural selection.
LOTKA-VOLTERRA MODEL : describes the relationship between 2 species that are competing for resources
Logistic Growth Equations:
Species 1 : dN/dt = rN (1 - N/K)
Species 2 : dN/dt =rN (1- N/K)
With the Competition Coefficient:
* alpha - per capita effect of species 2 on 1
* beta - per capita effect of species 1 on 2
* K = carrying capacity
* N = population size
Now, the Equations:
Species 1 : dN/dt = rN [1 - (N1 + alphaN2/K)]
Species 2 : dN/dt = rN [1 - (N2 + betaN1/K)]
These alpha and beta terms basically convert the population size of the one species into the equivalent # of individuals of the other.
HOW? let’s say Species 1 herbivore is grazing on grass but is twice the mass of Species 2 that is also grazing on the same grass, that means 1 is consuming it at twice the rate…so alpha = 2.0 & beta = 0.5.
The best way to show the outcomes of these equations is through graphs.
1st though:
ZERO-GROWTH ISOCLINE : represents the combined values of population size for Species 1 (N1) and Species 2 (N2) at which the pop. growth rate of both species = 0 (dN/dt = 0). When does this occur? When the combined pop. sizes = K, the carrying capacities.
Now, to solve for the combined values of N1 and N2 where growth rate of Species 1 = 0 (dN/dt = 0). That end part of the Species 1 equation will tell this rate: N1 + alphaN2 = K1. Yes, the combined values of N1 and N2 equal the carrying capacity (K) of Species 1.
This is done for solving for the y-intercept and the x-intercept and then drawing the line between those 2 points on the graphs. Any point along that line represents ZERO GROWTH (zero isocline) for Species 1 (13. a)) and the bottom graph, Species 2 (b).
Any point below the line? Species 1 grows (until it reaches the zero growth line)
Any point above the line? Species 1 declines (until it reaches the zero growth line)
SAME WITH THE BOTTOM GRAPH for Species 2
LOTKA-VOLTERRA PRINCIPLE:
THERE ARE 4 POSSIBLE OUTCOMES OF THIS COMPETITION: to interpret the combined dynamics of the 2 competing species, their isoclines need to be on the same graph.
Equilibrium Point : the big dot in the middle equals the combined population sizes of the 2 species. It’s N1 + N2 = 0.
Unstable Equilibrium : any point on the rest of the graph means it’s unstable. If either N1 or N2 change and move away from the equilibrium point, then it’s considered an unstable equilibrium BECAUSE one species will eventually lead to the extinction of the other.
SO, 3 of the 4 scenarios leads to the extinction of the other species.
Competitive Exclusion Principle : states that ‘complete competitors’ can’t coexist. Complete competitors are 2 species (not interbreeding) that live in the same place and have exactly the same ecological requirements. (So if Species A increases their population even a small bit faster than Species B, then Species A will eventually cause Species B’s extinction.) Basically, if 2 species have identicall resource requirements, then one species will eventually displace the other.
Graph 4 shows the arrows moving AWAY from the equilibrium point, so these will be ‘unstable equilibrium’.
Niche: range of physical and chemical conditions under which a species can survive and reproduce.. The specific role that a species occupies within an ecosystem – interactions with other species, how it uses it’s resources, how it interacts with its environment.
(Habitat: physical environment where the species lives. Includes temp, humidity, vegetation, food, soil type.)
Niche Differentiation: the process by which similar species evolve different ecological roles or niches in order to reduce competition for limited resources, by exploiting resources that are unavailable to other species. Reduces directly competiting for the same exact resources. Why? Allows coexistence. So different feeding strategies, habitat preferences, feeding at different times of the day, different sizes/amounts of nutrients.
a) Resource Partitioning: observable outcome of niche differentiation. Species divides or partitions available resources among themselves. Why? Minimizes direct competition. Allows coexistence. Allows more efficient use of resources.
ex: There are 3 plants on the prairies. One has a long tap root that goes below the rooting zone of the other 2. One has a very shallow, fibrous root system, and the 3rd plant has a root system that branches out in the root zone between the shallow and the deeply rooted one.
The niche is a multidimensiional hypervolume (see pic below) with each of the 3 dimensions being something that the species needs for survival and reproduction.
Non-Resource Factors that affect Competition:
Features of the environment, others than resources ALSO affect the growth/reproduction of a species:
* temperatures
* water pH
* humidity
* salinity
* soil pH
Interference Competition (for foraging sites) is an important factor that influences the success of individuals where species coexist.
Ex: for the 3 types of trout, one ate more food at 4 C, but at the highest temp of 28 C, another trout ate the most resources. This pattern of food consumption shows changes in the relative competitive abilities of the the 3 fish.
Ex2: tadpoles of 2 species of tree frogs have broadly overlapping geographic regions. But respond to different water pH. Low 4.5 pH = low interspecific interactions. High pH 6.0 caused inspecific competition from one tadpole to the other and the 2nd one had decreased survival and increased larval period, with decreased size at metamorphosis.
So, as the environmental conditions change, the relative competitive abilities of species also changes.
What causes these shifts in competitive ability?
1. Carrying capacity changes (values of K)
2. Physical environment changes that affect resources availability
Fundamental Niche: theoretically the full range of evnvironmental conditions and resources a species could utilize – w/o interacting with other species. Theoretical potential to survive/thrive/reproduce, but in reality, various abiotic (environmental) and biotic (other species) restrict a species from fully utilizing it’d fundamental niche. (aka. ‘physiological niche’)
a) Chemical Conditions in a Niche: Oxygen levels, nutrient availability (including nitrogen or phosphorous for plants), salinity, toxicity tolerance, pH levels.
b) Physical Conditions in a Niche : temp range, humidity, soil type, topography, shelter.
Ex: Polar Bear (Ursus maritimus) has chemical conditions (marine food high in fat to deal with freezing conditions) and physical needs (cold temps, ice habitat, snow cover in order to hunt seals, insulated fur coat for arctic weather).
Realized Niche: represents the actual, practical, observed habitat and resource utilization of a species, with interactions of other species. Often narrower due to predation, competition, disease because it restricts their use of space, range of foods, nesting habitats, etc.
Fundamental + Realized = Ecological Niche
In the example of the 4 chipmunks, each of them have inhabitated a different altitudinal zone:
* Contact zones are determined by interspecific aggression
* Range is determined by aggressive exclusion and its ability to survive and reproduce in the different environments
Competitive Release : when a species expandes it’s niche, due to reduced interspecific competition
* happens when a species inhabits an area with no competitors
* when the competitors are taken out of an area and the others are allowed to expand!
Ex: gray wolf populations decreased in North America, so coyotes have dramatically increased in population. This was quantified by reintroducing wolves back into the environment.
Character Displacement: when this shift, this phenotypic divergence, involves morphological features, such as evolving a smaller beak size due to another species having a bigger beak and eating all their seeds, behaviour, or physiology.
Why the shift? Due to competition.
