Species Interactions Flashcards
Community ecology
Interactions among different species have 2 important results:
- They affect the distribution and abundance of the interacting species
- They are agents of natural selection and affect the evolution of the interacting species
Species interactions
+ : a relationship between 2 species providing a fitness benefit to members of one of the species
- : a relationship that hurts members of one of the species
0 : a relationship that has no effect on the members of either species
Interactions: -/-, +/-, +/+, or +/0 (commensalism)
3 themes in community ecology
- Species interactions may affect the distribution and abundance of a particular species
- Species act as agents of natural selection when they interact; a co-evolutionary arms race occurs between predators and prey, between parasites and hosts, and between other types of interacting species
- The outcome of interactions among species is dynamic and conditions; interactions among species can change
Coevolution
The process where evolutionary changes in the traits of one species results in evolutionary changes in the traits of a different species; can involve predators and prey, hosts and parasites, an other kinds of interactions
Competition
A -/- interaction that occurs when individuals use the same limiting resources
Intraspecific competition
Competition that occurs among members of the same species; major cause of density dependent population growth
Interspecific competition
Competition occurs between members of different species
Consumptive competion
When two species consume the same resources
Preemptive competition
When one species makes space unavailable to another species
Overgrowth competition
One species grows above another
Chemical competion
When one species produces toxins that negatively affect another species
Territorial competition
Mobile species protects its feeding or breeding territory against other species
Encounter competition
Two species interfere directly for access to specific resources
Niche
The range of resources that a species is able to use, and the range of conditions that it can tolerate
- interspecific comp. occurs when the niches of two species overlap
- area with minimal resources, specialist will do well
- area with numerous resources, generalist will do well
Exclusion principle
Two species which compete for the same limited resource cannot coexist at constant population values
Asymmetric competition
When one species has a much greater fitness reduction than the other species
Symmetric competition
When the fitness reduction in both species is approximately the same, or equal
Competitive exclusion
The competitive exclusion principle states that it is not possible for species with the very same niche to coexis
Fundamental niche
The total theoretical range of resources, habitats and conditions used/or tolerated when there is no competition
Realized niche
The portion of the fundamental niche that a species actually occupies; the resources, habitats, and conditions used/or tolerated when there is competition
Niche differentiation
An evolutionary change in the traits of a species that reduces the amount of niche overlap (also called resource partitioning); this reduces competition
Character displacement
Evolutionary changes in the traits of species during the process of niche differentiation
Consumption
+/- interaction; one organism eats the other; increases the fitness of one and reduces fitness of the other
Major types of consumption
- Herbivory
- Predation
- Parasitism
Constitutive/standing defences
Defences that are always present (i.e. camouflage, schooling, weaponry, mimicry)
Inducible defences
Only present when a predator or consumer is present; induced in response to the presence of the predator
Aposematic colouration
A bright warning of dangerous or noxious defences; effective on visual predators (learn to avoid these patterns)
Mullerian mimicry
When harmful species resemble each other; increases the chances that predators learn to avoid them
Bayesian mimicry
When harmless species resemble harmful species; predators avoid harmful species and harmless species get a “free ride”
Community structure (4 elements)
- The total number of species
- The same of interactions among all species
- The relative abundance of those species
- The physical attributes of the community (geographic size, temperature, pressure) as well as biotic factors such as major vegetation type (biome)
Species richness
The number of different species in a given area
Species abundance
The number of individuals within a species (or each different species) in an area
The Shannon Diversity Index
H’ = - sum of pi ln pi
H’ = species diversity
pi = the proportion of species i
Keystone species
Has a bigger effect on the entire ecosystem than any other one species; greater impacts on a community than either its abundance or biomass suggest
Top-down control
Affects trophic levels underneath keystone predators
Ecosystem engineers
Cause physical changes in the environment that affect community structure (i.e. beavers)
Keystone prey
Species that have major input in the amount of nutrients and nutrient cycling within an ecological system; their removal would disastrous for the diversity of ecosystem
Bottom-up control
Introduced something at the bottom; affects trophic levels above it
Bottom-up influences
When nutrients, sunlight, temperature, moisture and other abiotic factors determine the number of primary producers (we have bottom-up control)
Top-down influences
Refers to the removal of predators or consumers at a higher trophic level having a strong impact on a lower trophic level
Trophic cascade
Changes in top-down control cause conspicuous effects two or three links away in a food web (increase-decrease-increase)
Frederick Clements
Biological communities are stable, integrated, and orderly entities with a highly predictable composition
- climax community
Henry Gleason
Community found in a particular area is neither stable nor predictable
- chance
Disturbance regime
Most communities experience a characteristic type of disturbance, and in most cases, disturbances occur with a predictable frequency and severity
Inherent edge
Naturally present and stable
Induced edge
Transitory; either natural disasters or human activity
Extirpation
Local extinction
Ecotone
Region of transition between two biological communities
Succession
The recovery that follows a sever disturbance
Primary succession
Occurs when a disturbance removes the soil and its organisms as well as organisms that live above the surface (i.e. glaciers, floods, volcanic eruptions)
Secondary succession
Occurs when a disturbance removes or all of the organisms from an area but leaves the soil intact, including microbes and seedlings
Successional pathway
The specific sequence of species that appears over time (after succession)
Pioneering species
The first organisms that arrive at a newly disturbed site; very high reproductive rates; can tolerate severe abiotic conditions; good dispersal ability; little competitive ability (trade off)
Facilitation
Occurs when early-arriving species make conditions ore favourable for the arrival of certain later species
Tolerance
Existing species do not affect the probability that subsequent species will become established
Inhibition
The presence of one species inhibit the establishment of another
Longitudinal diversity gradient hypotheses
- High-productivity hypothesis: high prod. Promotes high diversity
- Energy hypothesis: high temp. Increases prod. and likelihood that organisms can tolerate he physical conditions in a region
- Time hypothesis: topical regions have had more time for speciation than other regions
- Intermediate disturbance hypothesis: regions with moderate type, frequency, and severity of disturbance should have high species richness and diversity
- Area and age hypothesis: land are and historical factors (i.e. glaciation)
All factors at influence diversity; no single hypothesis can give explanation
