Population And Community Ecology Flashcards
What is Population Ecology
The study of populations in relation to the environment, including environmental influences on density (increase or decrease) and distribution (clump or spread out), age structure, and population size
Population density (2)
- Describes the number of individuals per unit or volume (ocean)
- D = M/V
Density-Independent Factors (3)
- Environmental conditions that affect a population regardless of its density
- Usually abiotic (non-living) factors like seasonal weather or natural disasters
- Cannot be controlled but end up changing the density
Density-dependent factors
Factors that affect the population growth as a result of density or population surrounding the area
Territoriality in relation to density
- May limit density
- Animals that use chemical communication to warn off same species of their boundaries (bad density)
- Animals bunch up together while having a close separation (good density)
Health and density
In dense populations, pathogens can spread more rapidly since physical contact between individuals increases
Density can influence health and survival
Stress and Density
- Crowded animals show increase in levels of stress as a result they act abnormally;
Stress can cause:
- aggression
- decrease in fertility (hormonal changes)
- reduce the population growth rate
Predation and density
With increased predation, the prey population decreases. This in turn, limits the predator population since less food available.With reduced predation the prey population begins to grow and the cycle is repeated
Competition and density
Interspecific competition: different species (decrease or increase one) = land, ressources, food
Intraspecific competition: same species = usually mates, or territory
Population Models Describe Population Size
The size of a population at any time depends on the balance between individuals being added to the population and individuals being removed from the population: death, birth, immigrations and emigration
Population change = B+I-D-E
Population change as a percentage
(B+I-D-E)/n x 100 = %
Determining Density in populations
Determining the density of natural populations is difficult and impossible
Techniques are used to estimate:
- Mark and recapture
- Quadrat sampling
- Random sampling
Mark and recapture
Formula: (total number capture) x (number marked)/ total number recapture with mark) = estimate size
Basic idea: 1. Capture a small number of individuals 2. Harmless mark them 3. Release them 4. Over the years capture geese and record their numbers
Random sampling
Basic idea: 1. Plots the area 2. Chooses random spots 3. Counts population in those specific plots 4. Averages 5. Multiplies to get the estimate
- doesn’t work great with animals that move around
Dispersion
Pattern of spacing among individuals within the boundaries of the population
The patterns of dispersion
Environmental and social factors influence spacing of individuals in a population
Types:
- clumped
- uniform
- random
Clumped dispersion
In a clumped dispersion, individual aggregate in patches (groups), usually influenced by resource availability and behaviour
Benefits: increases the effectiveness of retrieving food, protecting and caring for young and exclude other individuals from territory (defending)
Uniform dispersion
In a uniform dispersion, individuals are evenly distributed, may be related by social interactions such as territoriality
Often exhibition of uniform spacing is maintained by aggressive interactions between neighbours but together easier to avoid predators
Random dispersion
In a random dispersion, the position of the individuals is independent of the others
What is a community?
A biological community is an assemblage of populations of various species living close enough for potential interaction
Community interactions
Affect species survival and reproduction
- Competition
- Predation
- Herbivory
- Symbiosis (parasitism, mutualism, commensalism)
- Disease
Competition
Occurs when species compete for a resource in short supply
-/-
Compétition Exclusion Principle
States that two species competing for the same limiting resources cannot coexist in the same place
Predation
Refers to interaction where one species, the predator, kills and eats the other, the prey.
-/+
Behavioural defenses to predation
Prey display various defensive adaptations:
- Behavioural defenses include hiding, fleeing, self-defense and alarm calls
- Also morphological and physiological defense adaptations
Cryptic Coloration
Cryptic coloration or camouflage makes prey difficult to spot (morphological - colour)
Chemical Defense
Physiological adaptation
Animal with effective chemical defense often exhibit bright warning coloration called aposematic coloration
Mimicry
A prey may gain significant protection by mimicking the appearance (morphological) or even the smell of another species (physiological) which in turn aids its survival
Parasitism
In parasitism, one organism, the parasite, derives nourishment from another organism, the host, which is harmed in the process
-/+
Disease
Pathogens, disease-causing agents are typically bacteria, viruses or protists
Reproduction faster than parasites
-/+
Mutualism
An interspecific interaction that benefits both species
+/+
Commensalism
One species benefits and the other is apparently unaffected
Very rarely seen in nature
+/neutral
Species diversity
Species diversity of a community is the variety of organism that make up the community (different species)
It had 2 components:
- species richness
- relative abundance
Species richness
Species richness is the total number of different species in the community
Relative abundance
Relative abundance is the proportion each species represents of the total individuals in the community
Relative abundance = number of individuals in one species/ total number of individuals x 100 (percentage)
Species richness in relation to species evenness
Species Richness - number of species in a community
Species Evenness - relative abundance of each species
If high in one species richness, low in species evenness (vice versa)
Keystone species
Keystone species are a species which other species in an ecosystem largely depend. If the keystone species were to be removed, the ecosystem would change drastically
- not necessarily abundant
- exert strong control on a community by their ecological roles
Exponential Growth
Ideal environment with unlimited ressources = J-shaped curve on a graph
Always growing
Logistic Growth
Population experiences a levelling off from exponential growth due to limiting ressources
- S-shaped
- carrying capacity = k represents the maximum population size that can be supported in an environment
Quadrat
