Ecology Lecture Notes

Sympatric Speciation

• Speciation occurs in geographically overlapping populations.

• Sub-groups diverge in a trait, such as feeding in different regions.

• Other traits also vary, including coloration and habitat.

• Mating is linked to feeding or color differences.

• Genetic divergence occurs, leading to two separate daughter species.

Reproductive Barriers

• Biological barriers that prevent members of different species from producing hybrids.

• Hybrids often have reduced fitness.

• Natural selection favors mechanisms against hybrids.

• Two major types:

  • Pre-zygotic

  • Post-zygotic

Pre-zygotic Barriers

• Habitat Isolation:

  • Species occupy different habitats.

  • Decreased probability of encountering other species.

  • Example: Garter snakes (water vs. land).

• Temporal Isolation:

  • Breed at different times of day or year.

  • Decreased probability of encounter while reproductively active.

  • Example: Skunks (summer vs. winter).

• Behavioral Isolation:

  • Courtship rituals that are species-specific.

  • Not recognized by other species.

  • Example: Blue-footed boobies.

• Mechanical Isolation:

  • Morphological differences prevent successful mating.

  • Differences in size or shape (e.g., snails).

• Gametic Isolation:

  • Sperm and eggs are not compatible.

  • Example: Sea urchins (sperm released into water to find eggs).

Post-zygotic Barriers

• Reduced Hybrid Viability:

  • Hybrid forms, but allele interactions impede development.

  • Example: Salamanders (hybrids are frail and can't compete).

• Reduced Hybrid Fertility:

  • Hybrid forms but is sterile.

  • Example: Donkey and horse produce a mule (sterile but robust).

• Hybrid Breakdown:

  • First generation hybrids are viable and fertile, but the second generation is weak and sterile.

  • Due to accumulation of recessive alleles (e.g., cultivated rice).

Genetic Drift and Speciation

• In large populations, genetic drift (XYZ rates) increases due to founder effects, increasing divergence among populations.

• Colonization of Islands (YZ, XY).

Taxonomy

• Theory and practice of classifying organisms.

• Taxon: Group of organisms treated as a unit for classification.

Classification System

• Linnaean System.

• Hierarchical inclusiveness changes with levels.

  • Species Name: Two parts - Genus (1st) and species (2nd).

    • Ambystoma opacum (italics) or Ambystoma opacum (underlined).

    • First letter of genus name capitalized, other letters lower case.

Classification Hierarchy

• Domain

• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

  • Inclusiveness increases from species to domain.

Phylogenetic Reconstruction

• Hypothesis of evolutionary relationships.

• Cladogram: Shared derived character states.

• Character: Wing.

• Character State: Present or absent.

• Character State Assignment:

  • Present: 0 (ancestral), absent: 1 (derived) OR absent: 0 (ancestral), present: 1 (derived).

Outgroup

• Group used for comparison.

• Possesses all ancestral character states.

• Zero values for all characters.

Ingroup

• Group whose evolutionary relationships you are trying to explain.

Approach to Phylogenetic Reconstruction

1. Define outgroup, ingroup, characters, and character states (ancestral - 0, derived - 1).

2. Construct character table (matrix) - matrix of 0 values and 1 values for each character/taxa.

3. Use character matrix to construct phylogeny based on shared derived character states.

Phylogeny

• General appearance with common ancestor and time axis.

• Taxon 1, Taxon 2, Taxon 3 with most recent common ancestor.

• Values can rotate.

Phylogeny of 3 Domains

• Bacteria (B)

• Archaea (A)

• Eukarya (E)

• Diagram showing common ancestors (C.A.) and evolutionary relationships.

• Examples of traits: V.C., H.J., Fovv, Legs, Amnion showing the evolution and common ancestors of lancelet, lamprey, frog, bird, and leopard.

Choosing among Phylogenies

• Use principle of parsimony.

• Assume the fewest evolutionary events occurred.

• Phylogeny with the fewest evolutionary events is preferred.

• Example: 6 taxa (A, B, C, D, E, O= outgroup), 5 characters (1, 2, 3, 4, 5) with a table showing character states and events.

Key Terms

• Sister taxa: Group of organisms that share an immediate common ancestor.

• Uniquely derived character state: Derived character state only present in one taxa.

  • Does not help resolve phylogenetic relationships.

  • Phylogenetically uninformative.

Clade

• Group that contains an ancestral species and all of its descendants.

  • Monophyletic group (clade): An ancestral species and all of its descendants.

  • Paraphyletic group: An ancestral species and some, but not all, of its descendants.

  • Polyphyletic Group: A group which includes distantly related species but not a recent common ancestor.

Scientific Method

• Random sampling, sample, inference, population.

• Optimal Sample Size:

  • Large enough to represent the true value of the population.

  • Not so costly in terms of finance and time.

Ethics

• What type of costs could be relevant?

Experimental Design

• Control Group: Group used for comparison; context-dependent.

  • Example: Control group with predators absent, experimental group with predators present.

• Drug Trial:

  • Experimental (active drug)

  • Control: Placebo (non-active; sugar pill)

  • Double-blind (patient and doctor don't know).

• Replicate:

  • Independent experimental unit (EU).

  • Unit used for analysis (e.g., each patient in a treatment group).

• Pseudoreplication:

  • False replicate - non-independent units treated as independent units.

Paired Designs

• Benefits of paired designs:

  • Increased replication.

  • Remove additional 'noise' due to variation among individuals included in the study.

  • Examples: twins, morning vs. afternoon, same vs. different location.

• Paired vs. unpaired analysis:

  • Experiment to examine if drug X influences blood pressure levels (BPL).

  • Two treatment groups: experimental (drug X) and control (placebo).

  • 20 patients.

Scientific Method - Results: Data Collection & Analysis

• Random Sampling leading to Sample used for Inference about a Population.

Why Use Statistics?

• Describe data.

• Test hypotheses to reveal general patterns.

• Provides an objective and consistent method.

Variables

• Characteristic that can be assigned a number or a category.

  • Categorical Variable: A variable that is assigned to a category (e.g., blood type, eye color).

  • Numerical Variable: A variable that is recorded as an amount (e.g., human weight, number of bacterial colonies).

Descriptive and Inferential Statistics

Descriptive

• Describes data (for the sample).

• Graphs, tables.

• Central tendency: Mean, median.
  Mean = {\sum{i=1}^{n} xi \over n}

• Dispersion: Standard deviation, interquartile range
  s = \sqrt{\frac{\sum{i=1}^{N} (xi - \overline{x})^2}{N-1}}

Inferential

• Analysis of sample data.

• Tests: e.g., \chi^2 test (categorical), t-test (numeric).

• Make decision about statistical hypothesis (null) for sample data.

• Interpret overall hypothesis.

• Make inferences about the population.

General Approach

• Generate hypothesis.

• Define H₀ (null) and Hₐ (alternative).

• Set critical value level (\alpha), typically at 0.05.

• Collect sample data.

• Calculate test statistic.

• Obtain critical value and p-value (Table).

• Make decision about H₀.

• Interpret original hypothesis.

P-value

• Probability that the results obtained are due to chance.

Alpha Value (Critical Value)

• Threshold used to determine if results obtained are likely due to chance.

Statistical Hypotheses

• H₀: There is no difference in DV between experimental and control groups.

• Hₐ: There is a difference in DV between experimental and control groups.

Decision Rule (H₀)

• If p < 0.05: Reject H₀

• If p > 0.05: Fail to reject H₀

• If p = 0.05: Fail to reject H₀

Error Table

• Type I error: False positive (reject H₀ when H₀ is true).

• Type II error: False negative (fail to reject H₀ when H₀ is false).

Ecology

• Scientific study of the interactions between organisms and their environment.

• Environment ↔ Organisms.

Factors in the Environment

• Abiotic Factor: Non-living (soil, weather, pH, temperature, wind, salinity).

• Biotic Factor: Living (organisms of the same or different species; competition, predation, parasitism).

Levels of Organization in Ecology

• Ecosystem (nutrient cycling, energy flow, human impacts).

• Community (multiple species; species diversity, food webs).

• Population (single species; #'s in nature, patterns in space and time).

• Individuals (behavior, physiology, morphology).

Ecology and Related Disciplines

• Physiology (metabolic rate, variation).

• Genetics (genetic diversity, gene flow).

• Behavior (communication, mating rituals, territoriality).

• Evolution (adaptations).

Research in Ecology

• Factors that determine the distribution and abundance of organisms.

• Behavioral Ecology: How animals make "decisions" that influence survival and reproductive success (e.g., diet choice).

Sexual Selection

• Two categories:

  • Intrasexual selection: Competition between members of one sex for mates.

  • Intersexual selection: Members of one sex choosing members of the other sex as mates.

Mating Systems and Behavior

• Two major Categories:

  1. Male & Female Monogamy.

     • eg grebes, macaroni penguins- “ecstatic dance”, gray. Wolves, swans- made for life.

  2. Male and Female OR

     • 1 female and male polygamy

     • eg: gazelles, elephants, tigers, gorillas →Intra-Sexual Selection (same site) uneven fight retreat (different size or same site) Uneven fight retreat (different size).

Social Monogamy

• Relationship appears monogamous, but not actually the case (e.g., red-winged blackbirds).

• Molecular analysis shows
  34% of nestlings were fathered by neighboring males.

Prairie Voles

• Females live longer with help from males.

Parental Care

• Needs of young are the most important factor in the evolution of parental care.

• Can young care for themselves?

  • Octopus:

    • Eggs: No

    • Young when developed/hatched: Yes

  • Strawberry poison dart frog:

    • Tadpole: No

    • Mom carries tadpole up a tree and deposits baby into bromeliad; feeds tadpole unfertilized eggs.

Certainty of Paternity and the Role of Paternal Care in Males

• Eggs still inside female during fertilization.

• External fertilization (fish and amphibians).

• Paternal care in
  7% of species with internal fertilization.

• Paternal care in
  70% of species with external fertilization.

• Higher certainty of paternity with external fertilization, so male stays to help care for the young.

Communication

• Transfer of information from signaler (sender) to receiver(s).

• Examples: Acoustic, chemical, visual.

Receivers

1. Legitimate receiver: Intended receiver (e.g., potential mate).

2. Illegitimate receiver: Unintended receiver (e.g., predator hearing the song of a bird trying to attract a mate; parasite female fly deposits her larvae on male cricket).

Signals

• Two types:

  1. Honest signal: True reflection of quality (of genes); very costly to produce and maintain.

  2. Dishonest signal: Sender manipulates the response of the receiver.

     • Sending out a dishonest signal means you are purposefully trying to trick individuals who will see or hear that signal.

Honest Signal Trade-Off

• Costs of carotenoids in bird and fish: Produce bright yellow, orange, red colors; must acquire in diet; cannot be used elsewhere (not in the immune system).

• Disadvantage of these bright colors:

  • Increase visibility to predators.

  • Increase aggression from rivals (male competition).

Honest Signal : Agnostic Behavior

• Agnostic behavior: A social behavior linked to fighting within a species.

  1. Aggressive behavior / threat.

  2. Submission.

Threat Displays

• Symbolic act that provides info to opponent about fighting ability.

• If large asymmetry in potential fighting ability, no fight.

• If lack of asymmetry in potential fighting ability -> fight (e.g., iguanas - ritual band biting).

Honest Signals are Informative

• Provide information to females about:

  1. Foraging ability, parenting ability.

  2. Immune system (indicates quality of genes).

  3. Physical Condition.

• All related to FITNESS - how good a particular genotype is at leaving offspring in the next generation.

Honest Signal Example

• Injury-related Chemical Cue (IRCC).
  *Common in aquatic systems. Chemicals are released into the environment following Injury.
  *Response by conspecifics (Individual of same species) appropriate / anti-predatory BehaviorSpecies specific. -> move away, hide, mob predator to get leave.

Minnows

Over time, if Selection for Response, we will see a shift of Response to cue. Directional Selection for IRCC.Frequency graphs of minnow responses to cue over time.

Dishonest Signal

• Sender manipulates the response of the receiver → purposefully trying to trick another individual.
  Ex: distraction display in parental birds.ex: predatory firefies- predatory female firefly species specific flashing pattern to in make air pattern male approaches in the grass- she mimics the flashing to mate- female eats male. Involuntary automatic.

Innate Behavior

• A response an organism is just going to be born with - something that is developmentally fixed (not learned).

• Stimulus triggers response.

• Example: 3-spined Stickleback - red models generated this instant aggressive response from male stickleback in tank put models in without any red coloring + no response within Species territoriality to get access to a mate.

Learned Behavior

• Three major types:

  1. Imprinting: Learning within first 24 hrs of birth; critical sensitive period (e.g., some young birds).

  2. Associative Learning: Make associations based on experiences (e.g., predator learning to avoid certain prey items; herbivore learns to avoid plants with bad toxins).

Social Learning

• Learn how to Solve problems from Watching others e.g
  hunting behavior is learned from watching older Individuals→ Cheetah moms teach Cubs to bunt* Type of behavior considered to be selfless.* Some Cost to Self.

Altruism

• An act that favors another individual at some cost to self.

Types of Altruism

1. Reciprocal Altruism - individuals involved Over non-relatives. Kin Selection - individuals involved are relatives and / alturistic act, but they are Kin so there is a genetic and fitness benefit.

Reciprocal Altruism

• Altruistic act for a non-relative, but they must reciprocal act (non-relative involved. Must → punish by withholding food).* unrelated individuals live in some way food (over in stop not by with internet defense they they feeding some way.

• Food is shared among wolves and deev feeding non-offspring
  reciprocate later.

• a long-term memory recognition who
  Condition : - must reciprocate the act- involved with non-reciprocity*Called Strategy cooperate other does.

Altruism- Kin Selection

• Involves Relatives Genetic component involved helping youger some younger conditions Non INC INC Kin Selection and is is to their help to help their with their offspring*Inclusive (AltruismKin to some. ( with populations populations time