Life History Strategies and Trade-Offs

7.1 Life history patterns vary within and among species
- Learning Objectives:
- Explain the role of genetics and the environment in controlling life history traits.
- Compare the benefits and costs of sexual versus asexual reproduction.
7.2 Trade-offs between life history traits
- Learning Objectives:
- Adaptive evolution must be demonstrated.
- Discuss trade-offs between the number and size of offspring, as well as offspring care.

The clownfish (Nemo) maintains symbiotic relationships with sea anemones, providing cleaning services, while the anemones offer shelter.
Adult clownfish (2-6 individuals) live in a single sea anemone, usually not related.

Genetics influences key decisions:
- How large to grow?
- When to begin reproducing?
- How many offspring to produce and of what size?
- How fast to grow?
Life history: A record of events concerning growth, development, reproduction, and survival.
- Key factors include:
- Age and growth at sexual maturity.
- Timing and amount of reproduction.
- Survival and mortality rates.
- Frequency of reproduction.
Life history strategy: Overall pattern regarding the timing and nature of life history events.
Fitness maximization aims for an unlimited supply of viable offspring.

Phenotypic plasticity: Allocation of resources pertinent to growth, reproduction, and survival|.
- Example: Ponderosa pines exhibit variable growth forms based on environmental conditions.

Polyphenism: A single genotype can produce several distinct morphs based on environmental cues.
- Examples:
- Spadefoot toad tadpoles have small omnivore and larger carnivore morphs. The carnivore morphs grow faster and are favored in ephemeral ponds.

Organisms face distinct selection pressures at different life cycle stages, leading to varied adaptive strategies:
- Small-size constraints at early stages can lead to higher predation risks.
- Complex life cycles may provide benefits like niche shifts and resource utilization.

Corals reproduce both sexually and asexually. This allows for both genetic diversity and continuity through cloning.
Meiosis and Fertilization: Essential processes for gamete production.

Isogamy: Gametes of equal size (e.g., some algae).
Anisogamy: Gametes of different sizes; usually, the egg is larger and nutrient-rich, while sperm tend to be smaller and more mobile.

Complex life cycles involve distinctive stages that may utilize different habitats.
Example: The soybean aphid has a life cycle that includes both sexual and asexual reproductive forms.

LACK CLAUTCH SIZE and its implications:
- Illustration: As clutch size increases, the survival rate of eggs generally decreases.
- Data shows a significant trade-off where larger clutch sizes lead to fewer surviving offspring.
Reproductive Allocation: Energy devoted to reproduction at the expense of growth can impact future fitness.

The relationship between egg size, number, and survival is crucial in predicting reproductive strategies across various species.

Common patterns include the relationship between size, fecundity, and survival, revealing trade-offs between creating many small offspring or fewer larger ones that may have a better chance of survival.

Examples of dormancy and dispersal strategies used by organisms to enhance survival and colonization potential.
Paedomorphosis in salamanders as a developmental strategy allowing for growth in a favorable larval habitat while retaining juvenile characteristics.

C-selection: Strategies of high population growth in recently disturbed habitats, characterized by rapid reproduction.
K-selection: Slow reproductive strategies as populations approach carrying capacity (K), focusing on quality over quantity of offspring.

Competitive plants: Demonstrate superior abilities to acquire resources.
Stress-tolerant plants: Slow-growing, not favored by herbivores, exhibit phenotypic plasticity.
Ruderal plants: Fast growth and heavy seed production set the baseline in disturbed habitats.

Common occurrence in fish like clownfish, where individuals change sex based on size and social structures to maximize reproductive output.