BIOL215 Notes
September 4, 2025
Community Ecology: study of all species of plants and animals living in the same place at the same time
Population Ecology: study of a group of conspecific individuals living in the same place at the same time
Behavioral Ecology: study of individual plant or animal
Ecological Genetics/Genomics
- Study of genetic variability and relation to ecological processes
- Each individual is different due to genetics and environment
- Leads to slightly different morphology and behaviour
- Variability is the norm
Genetic Variability
- Originates with mutation -> different allele
Less individuals, more inbreeding
More inbreeding, more homozygosity
More homozygosity, more juvenile mortality
Minimum Viable Population Size
- Retention of 90% of genetic variability after 200 years
Minimum Viable Area
- minimum land area required to maintain genetic variability after 200 years
Natural Selection
- Non random and differential repetition of genotypes resulting in preservation of favourable variants
Adaptation
- Modification that enhances survival and reproductive success
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September 8, 2025
Optimal Foraging Theory (OFT) - optimizing choice of food
Food with greatest net energy gain (more energy in than out)
Feed more selectively when food is abundant
Low quality food when profitable food is scarce
Quality of food
Food differs in intrinsic quality
Sodium
Primary extracellular ion with a major role in bodies
Patch Foraging Time
Food occurs in patchy distribution and in patches of different size
Basic rules
concentrate forage in productive patches
Stay with patch until profitability falls to level equal to the average for all foraging patches combined
Length in patch should depend on achieving max joules/unit time
Longer the travel time, longer you should forage; vice versa
Territoriality - Active exclusion
Common in:
Predators, nesting birds, fish during reproduction, social insects, dragonflies
Home range
The area over which an animal travel which is not protected
What influences size of territory?
Body side, aggression, quality of area, competition, etc.
Where benefits maximally exceed costs
Sex and Mating Processes
- Asexual
o Offspring genetically identical to parent
o Prevalent in unchanging environment
§ Short lifespan
- Sexual
o most multicellular species
o Genes from two individuals combine, forms new genotypes
- Categories
o Dioecious
§ Two sexes
o Monoecious
§ Male and female organs on same individual
§ Simultaneous hermaphrodite
· Both sets of reproductive organs at same time
§ Sequential hermaphrodites
· male and female reproductive parts develop at different times during ontogeny (growth)
Mating Structure (with whom?)
- Panmixis
o unrestricted random mating
o All opposite sex individuals in a population are potentials
o Sexes usually look alike (monomorphic)
- Polygamy
o many marriages, multiple partners
o widespread in many species
o sexes look different (dimorphic)
§ males look better
- Polygyny
o many females
o males mate with many females
o females mate with very few males
o A1
§ Female defence polygyny
· individual males defend group of females
o A2
Resource defence polygyny
- Monogamy
o One marriage
o High fidelity to single partner (swans, hawks, beavers, wolves, etc.)
o Takes both parents to raise the kids
o Sexes usually look alike (monomorphic)
Mate Choice
- Tendency for an individual to be selective in whom they choose to mate with
- Females tend to invest more than males into reproduction and parental care
- Fitness of offspring influenced by genetic makeup
- Females choosier than males as fitness cost of making wrong choice is greater than males
- Female fitness increased by maximizing genetic quality and genetic variability of their offspring
- Male fitness is increased by maximizing # of fertilized eggs
- Males therefore compete with other males for access 78 females Cateria for mase choice by females
Criteria for Mate Choice by Females
- Nuptial gift
o Male brings resource, food, territory, etc
o Female uses characteristic of gift to determine quality of male
o Common in "behaviorally complex" animals
o Ex. Hanging fly -> prey gift
§ Bigger the prey gift, longer the allows him to mate for
- Dominant/Strong male preference (ex. elephant seal)
o Equal sex ratio in the wild
- Handicapped male hypothesis
o Displays by males that are costly to produce and maintain provide the female the greatest reliable info on genetic quality of the male
o If male can survive to adulthood with such handicap, it is an honest signal of fitness
o Ex. Peacocks, elk
Parasite Free Mall Hypothesis
- Susceptibility to pathogens which can lead to mortality in young
- Resistance to disease is heritable
- Males with no parasites have better immunological genes and improved physiological ability
- Bright nuptial displays are physiologically costly
- Females who choose bright color males are providing offspring with better genes that have better resistance to disease
Symmetrical Mate Hypothesis
- Minor errors in embryological development and growth can result in asymmetrical structures (developmental instability)
- Stress, pollution, parasites, etc. leads to asymmetricality
- Called fluctuating asymmetry
- Asymmetry can affect performance
Display Evaluation
- Females evaluate quality, complexity, coordination of displays
Inbreeding Avoidance
- All animals or plants in the wild have one or more mechanisms to avoid inbreeding (homozygosity)
- Many can detect wrong pheromones
- Females prefer males with the most dissimilar odor to themselves
- In one study, only exceptions were females on the pill who preferred males most similar to themselves
o Mimics pregnancy
o Females chose to be near family and non-kin when pregnant
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September 15, 2025
Advantages of Group Living
- Increased food search efficiency
- Increased capture efficiency
- Increased detection of predators (“many eyes” theory)
- Increased defense against predators (selfish herd theory, dilution effect)
- Each individual looks out for themselves but is less likely to be attacked when in a group
Disadvantages
- Resource depletion, sharing limited resources
- Increased transmission of disease/parasites
- Conflicts/stress
Life Histories
- Set of rules and choices to an individual’s schedule.
1) Reproductive effort = total allocation that an individual makes for reproduction.
a. Categories of reproductive effort:
b. R-selected
i. High # of eggs, seeds, offspring
ii. High population growth potential (“boom or bust” cycle; maximize reproductive capacity)
c. K-selected
i. Low # of eggs, seeds, offspring
ii. Low population growth potential
iii. Stable populations
iv. Usually long-lived individuals
v. Populations near carrying capacity
2) Frequency of reproduction:
a. Semelparous
i. breed once and die (e.g., salmon).
b. Iteroparous
i. repeated reproduction (e.g., humans, most plants, cetaceans, etc.).
3) Occurrence of parental care:
a. Common in bees, ants, birds, mammals, etc.
b. Uncommon in most insects, sharks, tuna, salmon, etc.
c. Amount of parental care varies among similar groups
d. Precocial
i. minimal care (shorebirds, grazing mammals, etc.)
e. Altricial
i. lots of care (born helpless; amphibians, most birds and mammals, etc.)
4) Clutch/litter size in K-selected species:
a. Shows how many young a female should have
b. Variation within and among species
c. All birds lay fewer eggs than they are capable of producing
d. Clutch size = max # of young parents can successfully raise (Lack’s hypothesis)
e. Laying more will impair both young and adult survival due to increased energy demands
f. Clutch size = max # of offspring that can be raised without a net reduction in future reproductive effort
5) Age at first reproduction (generation time):
a. Correlated with body size
Terms for Geographical Distribution of Species
- Cosmopolitan
o Could be on all continents or in all oceans (e.g. humans, rats, orcas)
- Widespread
o A few continents
- Limited
o Smaller area
- Highly restricted (endemic)
o E.g., Spirit bear, very small area
Types of Distribution
Dispersion (Statistical Concept)
Hyperdispersion
Equidistant from each other
Random
Distributed with no respect to others.
o Aggregated or clumped
§ Most common
Coarse-grained
Separated by large areas
Fine-grained
Separated by small areas
Major reasons for clumping
Plants
Local differences in microhabitat.
Animals
Resources
Movement of Individuals
A. Dispersal
a. Movement of individuals away from the immediate environment of birthplace
B. Migration
a. directional movement of large numbers of individuals between geographically distant locations.
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September 18, 2025
Density: Number of individuals per unit area/volume
a. Absolute density
a. Total counts
i. Photographic
b. Quadrat sampling
i. Establish a real or virtual grid, count every square in the grid, randomly choose a number of them, count number of individuals in each, find average to estimate the total number of individuals in whole area.
1. More squares you count, more accurate you are
c. Mark, release, recapture (N=pop size, M=marked fish, n=# of fish in new sample, m=# of marked fish in new sample)
i. Live capture, mark and release (ex. Catch and tag 5 fish)
ii. Resample the population later in time (ex. Catch 10, 2 are tagged, therefore 25 fish in population [M/N = m/n]) (N=m/n x M)
iii.
iv. Schnabel Method
1. Do this multiple times and mark them differently every time
v. Essential assumptions for reliable population estimate in mark-recapture studies
1. The population is largely constant over the duration of the mark-recapture studies
a. No immigration, no emigration, no births, no deaths
b. Only possible in short time frame
2. Marked individuals have the same chance of getting caught as unmarked individuals
a. Assumption of equal catchability
3. Marked individuals do not incur greater mortality as a result of the capture or mark
a. Stress-related mortality
b. Mark-associated mortality
4. Marked individuals do not lose their marks
d. Non-invasive methods using genetic markers (genetic fingerprinting)
i. Collect hair, feathers, faeces, scales
ii. Identify individual genotypes
iii. Resample at future time
iv. Estimate population size
Life Table Construction – Demography
a. Useful for estimating mortality rates, survival rates, survivorship curves and average life expectancy
o Age-specific analysis
§ Ex. Follow a cohort of eggs produced by adults in a population for 2 years
o Time-specific life table
§ Age structure at a single point in time
§ Long-lived animals (large animals)
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Random Day Somewhere
Life Tables & Net Reproductive Rate (R₀)
- Sex ratio critical → female numbers determine growth.
- Life tables often track only females.
- Lx = survivorship to beginning of age interval.
- Mx = avg. daughters produced by females in that interval.
- LxMx = product (survivorship × fecundity).
- R₀ = Σ LxMx = avg. # of breeding daughters per female over her life.
o R₀ < 1 → population declines.
o R₀ = 1 → population stable.
o R₀ > 1 → population increases.
- Example: Lions R₀ = 1.33 → population grows to 133 females per 100 each generation
Geometric (Discrete) Growth
- Applies to semelparous species (breed once & die, no overlapping generations).
- Equation: Nt+1 = R₀ × Nt
- λ (lambda) = geometric growth rate = Nt+1 / Nt.
o Finite multiplication rate (per generation).
- Equation using λ: Nt = N₀ λᵗ
- Examples:
o Beetles: λ = 1.25 → N₈ = 298 from 50 initial.
Bacteria doubling (λ=2): after 10 hrs → 1,024; after 25 hrs → ~33 million
Exponential (Continuous) Growth
- Applies to iteroparous species (most vertebrates, plants, many invertebrates).
- Equation: dN/dt = rN
dN = rate of change in numbers
dt = rate of change in time
dN/dt = rate of population increase
r = intrinsic rate of increase = birth rate (b) – death rate (d).
- Integrated form: Nt = N₀ eʳᵗ
- Alternative method for calculating r:
- r > 0 → growth, r = 0 → stable, r < 0 → decline.
- Estimate r from R₀ and generation time Tc: r ≈ ln(R₀)/Tc.
o Example: Lions → R₀=1.33, Tc=5.4 yrs → r=0.053 → +5.3%/y
Carrying Capacity (K) & Logistic Growth
- K = maximum sustainable population size in habitat long-term.
- Logistic model: dN/dt = rN (K–N)/K
- Growth slows as N approaches K.
- At K → growth = 0
- Early stages: rapid (high unutilized potential), middle: max growth, late: asymptote.
- Examples:
Reindeer on Pribilof Islands → overshoot then crash (chaotic logistic).
Yeast in broth → smooth logistic leveling at K.
Insects → damped oscillations or stable limit cycles
Density-Dependent Regulation
- Intrinsic factors: population growth tied to individuals’ activities.
- Most limiting resource sets K (food, water, space, nutrients, oxygen).
- Regulation occurs by ↓birth rates, ↑mortality, or both.
Mechanisms (when N > K):
Intraspecific competition
Interference (fighting, kleptoparasitism – gulls, lions).
Exploitative competition (plants competing for water, nutrients → “law of constant final yield”).
Delayed breeding/reduced fecundity
High density = fewer offspring per female (elk calf recruitment, bird clutch size).
Mediated by stress hormones → reduced growth, reproduction, immunity.
Territoriality
Dominant individuals secure larger territories → fewer subdominants breed.
Dispersal
Stabilizes populations (e.g., vole enclosure experiments).
Parasites/disease
Spread faster at high densities (e.g., myxomatosis in rabbits → 99% mortality).
Predation
High prey density supports more predators → greater proportional predation
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September 22, 2025
Key Definitions
Elton’s niche
The role of a species in a community (its “profession”).
Hutchinson’s niche
All biophysical conditions characterizing a species’ life.
Fundamental niche: entire range of conditions where species can function without limiting factors (prospective ecospace).
Realized niche: actual conditions occupied, limited by predators, competitors, parasites (actual ecospace).
Fundamental vs. Realized Niche
Fundamental niche = potential habitat use without biotic constraints.
Realized niche = restricted by competition, predation, parasitism.
Ex: barnacles (Chthamalus vs. Balanus) – fundamental overlap, but competition limits realized niche.
Quantifying Niche
Resource utilization curves
d = distance between two species’ mean resource use.
w = niche breadth (width of resource spectrum used).
If d/w < 1 → high overlap, low coexistence.
If d/w > 3 → low overlap, coexistence possible.
Resource partitioning allows coexistence by reducing overlap.
Niche Dimensions
Niche can be visualized as n-dimensional hypervolume.
2-D example: bird species differ in prey size + foraging height.
→ Some overlap tolerated, but too much = exclusion.More dimensions → more space for coexistence.
Niche Overlap Examples
Bird species A, B, C eating beetles
A & B overlap a lot → strong competition.
A & C minimal overlap → easier coexistence.
Resource partitioning reduces direct competition.
Competition Coefficients (α)
Measure of inhibitory effect of one species on another.
α = 1 → one indiv. of species 2 = one indiv. of species 1 (equal impact).
α = 0.1 → 10 indiv. of species 2 = one indiv. of species 1 (weaker effect).
Integrated into Lotka–Volterra competition models
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September 25, 2025
Density-independent population regulation
- Reduction in carrying capacity of the habitat
- Mainly due to extrinsic factors
- Mortality due to severe external conditions (ex drought, hurricanes, fires, etc.)
- Largely independent of numbers of individuals in population
Habitat: the physical place where an organism lives (ex. Desert, grassland, lake)
Niche: how an organism makes its living, two species with the same niche cannot coexist
Competition: occurs when an individual/population shares 1+ resources with 1+ other organisms and the use reduces the availability of said resource; interspecific (among species) and intraspecific (within species)
Resources: contribute to population growth and whose availability to other consumers can be reduced as a consequence of being occupied or consumed
Justin Von Liebig (1803-1873)
- German chemist with first chem lab
- Identified N as the major resource for plants
Liebig’s Law of the Minimum
- Population # can be regulated by a single resource that has the greatest relative scarcity