Comprehensive Study Notes on Natural Selection, Species Interactions, and Behavioral Ecology
Sexual Selection and Natural Selection (Section 23.3)
Sexual Selection Types
Intersexual Selection: This refers to the selection of an individual of one sex for mating by an individual of the other sex. This is often termed "mate choice."
Intrasexual Selection: This occurs when individuals of the same sex compete with one another to obtain mates.
Hypotheses and Contradictions in Sexual Selection
Elaborated Traits: Traits that attract members of the opposite sex tend to be more highly elaborated in males.
Investment Hypothesis: One common hypothesis is that eggs are expensive and sperm are cheap. Consequently, females generally invest more in their offspring than do males.
Behavioral Generalizations: The traditional view is that females are choosy about mates while males are willing to mate with almost any female. However, there are significant contradictions:
In some species, males invest more in parental care than females.
Sexual selection context varies with mating strategies: some females benefit from being promiscuous, while some males benefit from monogamy.
Selection Strength: It is hypothesized that any allele increasing a male’s attractiveness or success in competition should increase in the population, suggesting sexual selection acts more strongly on males.
Contradiction: If there are more females than males in a population, sexual selection on females can actually be stronger.
Environmental Context: In reality, sexual selection varies depending on the environmental context, the availability of mates, food, and other factors at a specific time and place.
Finding Mates and Sexual Dimorphism
Honest Signals: Organisms select traits that serve as honest signals of health and genetic quality. Examples include bright feathers or bright beaks.
Desirable Behaviors: Some honest signals indicate the ability to provide resources or care, such as building a nest or caring for eggs.
Access to Mates: Some species compete for access by fighting and establishing territory.
Sexual Dimorphism: This is when individuals of opposite sexes in the same species differ in traits. This includes:
Elaborate ornamentation.
Body size differences.
Physical weapons.
Courtship displays.
Key Takeaways on Selection and Ecology
Concurrent Selection: Multiple forms of sexual and/or ecological selection can occur simultaneously in the same population. These may favor the same phenotypes or result in fitness trade-offs.
Allele Frequency: Alleles responsible for adaptive morphological, physiological, and behavioral phenotypes increase in frequency over time.
Dynamic Context: Selection changes over time and space because it occurs within the context of ecology, which is inherently dynamic.
Species Interactions (Section 52.1)
Mutualism (): Interactions where both species benefit. These benefits vary from survival to reproduction.
Example (Nectar Bats): Orange nectar bats visit flowers to drink nectar for food; in the process, they carry pollen from one plant to another.
Example (Mycorrhizal Fungi): These fungi receive sugars and carbon compounds from plants in exchange for nitrogen and phosphorus acquired by the fungi.
Symbiosis: Any physically close association between two species, regardless of whether the interaction is positive, negative, or neutral. This implies that parasitism is a form of symbiosis.
The Nature of Mutualism
It is not the result of altruism; it is the byproduct of two individuals pursuing their own self-interest to maximize fitness.
It is sometimes referred to as "mutual parasitism."
Cheating in Mutualism: Some species cheat on mutualistic systems (a interaction).
Deceit Pollination: A plant displays a flower but provides no nectar.
Nectar Robbers: Organisms that pierce through the side of a flower to get nectar without providing pollination.
Context Dependency:
Low Nitrogen Soils: Plants invest resources into root nodules to support nitrogen-fixing bacteria (). The benefits of nitrogen outweigh the energetic costs.
High Nitrogen Soils: The costs of supporting bacteria may outweigh the benefits ().
Specificity:
Specialist Pollinators: High fitness from adapting to a single flower, but risk extinction if the flower disappears.
Generalist Pollinators: Less efficient at feeding but more likely to persist in variable conditions.
Consumption and Natural Selection
Coevolutionary Arms Race: A repeating cycle of reciprocal adaptation where species constantly adapt to each other to survive, influencing each other’s evolution.
Constitutive Defenses (Standing Defenses): These are present even in the absence of consumers.
Cryptic Coloration/Object Resemblance: Camouflage.
Mimicry:
Batesian Mimicry: Natural selection favors a mimic species that resembles an unpalatable species despite the mimic being nontoxic.
Mullerian Mimicry: Natural selection favors mimic species that are both unpalatable. This increases the likelihood predators avoid them and boosts fitness for both species.
Escape Behavior: Quick movement.
Toxins/Defense Chemicals: Poison or noxious substances.
Schooling/Flocking: Safety in numbers.
Defense Armor: Thorns, shells, weapons.
Cost: These defenses are effective but energetically costly.
Inducible Defenses: Defensive traits produced only in response to a consumer.
Traits: Can be physical, chemical, or behavioral.
Benefit: Energetically efficient because they decline in the absence of consumers.
Cost: There is a time lag; they are slow to produce.
Behavioral Ecology (Section 50.1)
Types of Causation
Proximate Causation: Explains how actions occur (genetic, neurological, hormonal, and skeletal-muscular mechanisms).
Ultimate Causation: Explains why actions occur based on evolutionary consequences and history.
Behavior and Natural Selection: Behavior can evolve by natural selection just like physical phenotypes.
Empathy: Social animals display high empathy and consolation behaviors toward friends and family, but not usually toward strangers.
Types of Behavior
Innate Behavior: Passed from parents to offspring; inflexible and does not adapt to environmental changes.
Learning: An enduring change in behavior resulting from specific life experiences. It is adaptive and helps survival in rapid change. The capacity to learn has a genetic basis.
Analytical Concepts
Fitness Trade-offs: Inescapable compromises (e.g., maximizing energy for food vs. energy for finding mates).
Cost-Benefit Analysis: Used to understand behavioral choices.
Key Principles
Non-conscious Choices: Non-human animals are not self-aware of their decisions; they are guided by neural and endocrine processes.
Individual Variation: Behavior varies within populations (e.g., some are more fearful or social), which is critical for evolution.
Energy Flow in Ecosystems (Section 53.1)
Primary Producers (Autotrophs): Synthesize food from inorganic sources.
Energy Transformation: They do not create energy; they transform sunlight/inorganic compounds into chemical energy (1st Law of Thermodynamics).
Gross Primary Productivity (GPP): The total amount of chemical energy produced in a given area/time.
Net Primary Productivity (NPP)
Primary producers use energy for cellular respiration () and growth/reproduction.
NPP represents energy invested in new tissue or offspring (biomass).
Efficiency: Energy is lost as heat/molecular waste (2nd Law of Thermodynamics).
Trophic Levels
Primary Consumers: Eat primary producers.
Secondary Consumers: Eat primary consumers.
Decomposers (Detritivores): Eat remains and waste.
Energy Dissipation: Energy flows through ecosystems and is lost as heat; it does not cycle.
Food Chains
Grazing Food Chain: Primary producers herbivores predators/parasites.
Decomposer Food Chain: Detritus primary decomposers predators/parasites.
Food Web: A complex diagram show all trophic interactions and energy transfer estimates.
Biomass Production and Transfer
Efficiency by Habitat:
Forest: Only of NPP is eaten alive due to indigestible wood.
Ocean: of NPP is eaten alive because algae lack tough structures.
The Rule: On average, only of total biomass in one trophic level is transferred to the next. The rest is lost to cellular respiration () and heat.
Biomass Efficiency Factors
Body Size: Large mammals are more efficient than small mammals because of a smaller surface-area-to-volume ratio, resulting in less heat loss.
Ectotherms vs. Endotherms: Ectotherms are more efficient at producing biomass because they spend less energy on cellular respiration and maintaining body heat.
Biomagnification
Pollutants: Includes heavy metals and Persistent Organic Pollutants (POPs).
Process Steps:
Large quantities are taken up by abundant primary consumers even if environmental concentration is low.
Primary consumers cannot metabolize or excrete pollutants, so they are retained.
Concentrations increase tenfold per individual with each successive trophic level.
Global NPP Patterns
Terrestrial NPP: Much higher than ocean NPP, especially in wet tropics.
Declines from the equator toward the poles (except in major deserts) due to decreased sunlight and temperature.
Marine NPP: Highest along coastlines and relatively high near poles.
Limiting Factor: Nutrients. Shallow coastal waters receive river nutrients and upwelling from deep cold water.
Open Ocean: Extremely low NPP because nutrients sink as dead cells and are unavailable at the surface.
Key Biomes: Tropical wet/dry forests cover less than of Earth but account for over of total NPP.
Aquatic Hotspots: Algal beds, coral reefs, wetlands, and estuaries.
Class Notes and Examples
Mutualism Example: Yucca moth pollinates flowers but also eats some of the seeds. It is mutualism because benefits outweigh costs.
Population Growth
Exponential Growth: Population size increases at an increasing rate (new populations, abundant resources).
Logistic Growth: Population stabilizes at the carrying capacity due to resources or predation.
Trophic Control Experiments
Kaibab Plateau (Mule Deer): Predator (cougar/wolf) removal.
Top-down control: If predators control prey, deer population increases when predators are removed.
Bottom-up control: If resources control prey, population continues to decrease regardless of predators.
Yellowstone: Introducing wolves reduced calves per cow. Female cows became more vigilant than males.
Trophic Cascade: Changes in one trophic level cause changes throughout the web (e.g., Zumwalt Prairie: cattle grazing affecting rodents and birds of prey).
Hubbard Brook Forest Efficiency Data
Approximately of incident sunlight becomes primary production.
Start: primary producer.
primary consumer ( efficiency).
secondary consumer ( efficiency).
tertiary consumer ( efficiency).
Behavioral Ecology Case Studies
Feather winged beetle: Sperm fills of its body size.
Spring tail: Leaves a "sperm fence" around females.
Pseudoscorpion: Guards sperm packets and eats competitors' packets.
Spectrum of Species Interactions
Mutualism (): Benefits outweigh costs.
Example: Tongue-eating isopod. It replaces the fish's tongue. While harmful initially, once the tongue is gone, the fish fares better with the isopod than with no tongue at all.
Commensalism (): One benefits, one is unaffected.
Consumption (): Predation and parasitism.
Neutralism (): No interaction.
Amensalism (): One unaffected, one harmed. Often occurs with massive size differences (e.g., elephant stepping on bugs; large tree shading small plants).
Competition ()
Interspecific: Between different species.
Intraspecific: Within the same species. This is often more intense because individuals have the exact same niche requirements.