Ecology: Environment, Interactions and Study

Ecology

• The scientific study of interactions between organisms and their environment.

Environment

• All factors outside the organism that influence it, including abiotic and biotic components.

Proximal vs. Ultimate Explanations

• Proximal explanations describe patterns based on the present environment.
• Ultimate explanations describe patterns based on the past environment.

Steps in Ecological Study

• The general process is: observe/discover, question, hypothesize, observe/sample/experiment/mathematical modeling, infer/conclude, and communicate results.

Heuristic Value

• Models have heuristic value as a process/rule meant to guide decision-making.

Evolutionary Ecology

• Focuses on individuals as the units of evolution.

Physiological Ecology

• Studies individual responses to the abiotic environment and population adaptations over generations.
• Often emphasizes animal responses to temperature fluctuations.

Behavioural Ecology

• Studies individual responses to other individuals (biotic interactions).

Evolutionary Hierarchy

• Encompasses: individuals, populations (same species interactions), and communities (multiple species interactions).

Ecosystem Ecology

• Deals with energy, nutrient, and chemical pathways.

Conservation Ecology

• Combines evolutionary, population, community, and ecosystem ecology.

Chromosomes

• Structures that contain DNA.

Genes

• DNA segments that code for proteins.

Locus

• The specific location of a gene on a chromosome.

Alleles

• Alternative forms of a gene.

Homozygote

• An individual with the same alleles at a locus (e.g., AA, aa).

Heterozygote

• An individual with different alleles at a locus (e.g., Aa).

Dominant Allele

• An allele that is fully expressed (A).

Recessive Allele

• An allele that is unexpressed (a).

Mendelian Inheritance

• Explains how breeding results in multiple allele combinations and maintains genetic variation.

Genotype

• All genetic characteristics of an individual, fixed during their lifetime.

Phenotype

• The interaction of an individual's genotype with its environment, not fixed during their lifetime.

Phenotypic Plasticity

• The ability of a genotype to alter its phenotypic expression under different environmental conditions.
  • Can be discrete (e.g., bees, ants) or continuous (e.g., daphnia).

Reaction Norm

• The relationship between a continuously varying trait and environmental conditions.

Evolution

• A change in the genetic composition of a population of a species over time.

Adaptation

• A genetically determined trait change in response to environmental conditions, enhancing the ability to cope.

Fitness

• An individual's proportionate contribution to future generations.

Natural Selection Assumptions

• Individuals of a species are not identical (genetic variation).
• Some variation is heritable.
• Individuals leave different numbers of descendants (varying fitness).
• Fitness depends on the interaction between an individual's traits and its abiotic and biotic environment.

Community

• A group of species inhabiting a given area and interacting directly or indirectly.

Food Webs

• Used to analyze community structure.

Hardy-Weinberg Principle

• Allele frequencies within a population do not change (evolution does not occur) unless mutations, non-random mating, random variations in fecundity/mortality, or natural selection occur.

Biological Species Concept

• Species distinguished based on their potential to interbreed and produce fertile offspring.

Speciation Steps

• Gene flow stops.
• Different selection pressures act on subpopulations.
• Genetic composition of subpopulations changes via natural selection.
• Subpopulations can no longer interbreed.

Allopatric Speciation

• Geographic isolation by a physical barrier.

Sympatric Speciation

• Subpopulations isolated without geographical isolation (e.g., timing of breeding).

Isolating Mechanisms

• Mechanisms that restrict gene exchange between subpopulations.
  • Premating: prevents mating, separation of mating events (behavioral, mechanical).
  • Postmating: reduced survival or reproductive success of offspring.

Climate

• The part of the physical (abiotic) environment that has the greatest impact on an organism.

Weather

• The combination of temperature, humidity, precipitation, wind, and cloudiness at a specific place and time as well as long term average pattern of weather.

Environmental Heterogeneity

• Variability in abiotic factors across space (due to Earth's atmosphere, solar radiation, rotation).

Aquatic Environment

• Features a low degree of microclimate variability in time and space.

Thermocline

• The region with the most rapid decline in temperature.

Thermal Stratification

• The process where surface water warms and becomes less dense than the water below.

Terrestrial Environment

• Features a higher degree of microclimate variability in time and space.
• Maintaining water balance has been a major influence on evolution.
• Life depends on soil.

Variation in Moisture-Holding Capacity

• Caused by climate, type of parent material (from which soil develops), topography (slope), aspect (north/south), and presence/absence/type of vegetation.

Responses to Environmental Changes

• Developmental (years, irreversible).
• Acclimatory (days-weeks, reversible e.g. fur coat).
• Regulatory (seconds-minutes, reversible e.g. shivering).

Poikilothermy

• (Conformers/Ectotherms) cannot maintain a constant body temperature (it varies).
• Regulate body temperature by gaining heat from external sources.

Homeothermy

• (Regulators/Endotherms) maintain a constant body temperature.
• Regulate body temperature by producing heat (metabolism).

Energy Conservation in Endotherms

• Lower the regulated temperature of a portion of their body (e.g., counter-current heat exchange in bird legs).
• Lower the regulated temperature at certain times of the day.
• Become larger (allometric relationship).

Torpor

• A temporary reduction in metabolic activity and lowered body temperature.

Hibernation

• An extended reduction in metabolic activity and lowered body temperature.

Photosynthesis

• Energy from the sun transforms CO2 into carbohydrates (simple sugars) and O2.
• Takes place in mesophyll cells.
• CO2 diffuses into the leaf through stomata.

Chlorophyll

• A light-absorbing pigment that traps light energy and synthesizes ATP.
• Dependent on the enzyme rubisco.

Respiration

• In the mitochondria of cells, carbohydrates are broken down to generate ATP, releasing CO2.

Transpiration

• As CO2 diffuses into the leaf, water diffuses out of the leaf and must be replaced by water taken up from the soil by roots.

Plant Parts

• Leaf: photosynthesis and CO2 uptake.
• Stem: structural support and access to light.
• Root: water and nutrient uptake from soil.

Plant Regulation (Short Time Scales)

• Plants regulate the opening and closing of stomata during different parts of the day.

Plant Regulation (Moderate Time Scales)

• Individuals can balance leaf vs. root tissue.
  • Wet conditions: more leaf tissue and less root and shoot.
  • Dry conditions: more root tissue and less leaf and shoot.

Plant Regulation (Long Time Scales)

• Modified forms of photosynthesis to increase water-use efficiency (e.g., C4 and CAM plants).
• Additional step in the conversion of CO2 into sugars for higher maximum rate of photosynthesis.

Shade-Tolerant Plants

• Adapted to low light.
• Lower production of rubisco in leaf tissue (lower maximum photosynthetic rate).

Shade-Tolerant Plant Compensation

• Higher production of chlorophyll.
• Higher leaf surface area.
• Higher growth of leaves than roots.

Shade-Intolerant Plants

• Adapted to high light.

Frost Hardening

• A genetically controlled characteristic where plants form protective compounds that act as antifreeze (sugars).
• Requires lots of energy, avoided by shedding leaves (deciduous species).

Temperature Drop Effect on Plants

• Temperature drops slowly: ice formation in the cell walls of leaves then cells dehydrate.
• Temperature drops rapidly: ice crystals form within the cell without dehydration.

Cold Temperature Adaptations

• Ice formation.
• Frost hardening.
• Deciduousness.

Functional Response

• The relationship between prey density and predator consumption rate (type I, II, III).

Consumption Rate Dependence

• Prey abundance per unit area (prey density).
• Search efficiency for prey (search time).
• Time to pursue, subdue, and ingest prey (handling time).

Type I Functional Response

• Rarely observed.
• Search time varies with prey density.
• Handling time is constant but near zero (e.g., spiders).
• Occurs if prey densities do not become high enough for satiation.
• As prey density increases, encounter rates increase and search time decreases.
• Search time is much greater than handling time.

Type II Functional Response

• Most common type.
• Search time varies with prey density.
• Handling time is constant and consumption rate levels off at high prey densities.
• To the left: as prey density increases, search time decreases (easier to find prey). Search time is much greater than handling time.
• To the right: as prey density increases, search time is zero but handling time remains constant. Handling time is much greater than search time.

Type III Functional Response

• Rarely observed.
• Search time and handling time vary with prey density, consumption rate is lower at low prey densities.
• At low prey density, search time and handling time increase.

Specialist

• An individual that takes one or a few prey types.
• Energy lost searching is offset by consuming more profitable prey.
• Handling time is much greater than searching time.

Generalist

• An individual that takes many prey types.
• Consume less profitable prey, resulting in low energy searching.
• Searching time is much greater than handling time.

Preference

• The proportion of a prey type in the diet is higher than in the environment.
• Depends on the energy and nutritional content of prey (vitamins, minerals).

Foraging Theory

• Goal: predict the optimal (or best) foraging strategy under certain conditions.
• Assumptions:
  • Foraging behavior enhances fitness.
  • Animals maximize net energy gain (energy loss: searching and handling time; energy gain: consumption).

Intraspecific Competition

• An interaction between individuals of the same species for a limited resource.
• Results in reduced survival, growth, reproduction, and fitness.
• Types: exploitation and interference.

Aggregative Response

• Individuals balance attraction to high resource abundance.
• Predators concentrate where prey density is high (due to high consumption rates).
• Increased probability of competition, but only if prey is limited.

Competitive Interactions

• Can lower consumption rates; the patch with the highest prey density is not always the best.

Exploitation (Scramble) Competition

• An individual responds to a decreased level of a limited resource exploited by other individuals.
• Individuals do not interact directly.

Interference (Contest) Competition

• An individual prevents another from exploiting a limited resource within a portion of the habitat.
• Individuals interact directly.

Density-Dependent

• Consumption rates decrease with increasing numbers of competitors.

Ideal Free Distribution (IFD) Assumptions

• There are a number of prey patches that vary in quality (environmental heterogeneity).
• Competitors are 'free' to exploit all patches (can move 'freely' among patches).
• Individual prey consumption rates decline with increasing numbers of competitors in the patch (resources in a patch are limited).
• Individuals have equal competitive abilities.
• Animals distribute themselves 'ideally' among patches to obtain the highest consumption rates (maximize net energy gain to ensure high fitness).

Ideal Free Distribution

• At the equilibrium distribution, the consumption rates of individuals are equal for all competitors in all patches.
• Can be a dynamic equilibrium.

Dynamic Equilibrium

• Individuals are constantly moving among the available patches.
• Individuals in the lowest quality patch will not gain access to more prey if they move to a higher quality patch.

Ideal Free Distribution Model

• Used to investigate how individuals balance attraction to high resource abundance and repulsion by the presence of competitors.

Prey Patch Selection

• Depends on both prey and competitor densities.

Life History

• An organism's strategic resource allocation between growth/survival and reproduction.

Life History Trade-Off

• Increased allocation of time/energy to some activities results in a decreased allocation to other activities (growth & survival vs. reproduction).

Reproductive Effort

• The proportion of available resources that an individual allocates to reproduction throughout its lifespan.
• Equals current plus future reproductive output.

Future Reproductive Output

• Survival plus fecundity (number of offspring produced) in the future.

Lifetime Reproductive Success (LRS)

• The number of offspring produced throughout the lifespan of an individual.
• Similar to fitness but does not consider offspring survival to reproductive age.

Life History Strategy

• Set of choices and decisions resulting in an individual's allocation to reproductive effort through its lifespan, aiming to maximize fitness.
  • Example strategies: invest heavily in current reproduction or invest heavily in current growth/survival.

Life History Traits

• Body size/growth (fecundity increases with body size).
• Age at sexual maturity.
• Number of reproductive events (parity).
• Number of offspring produced per event (fecundity).
• Offspring size.
• Amount of parental care.
• Senescence, programmed death (termination of life).

Life History Strategy Questions

• How often to breed?
• When to begin producing offspring?
• How many offspring to produce in each breeding event?

Life History: How Often to Breed?

• Semelparity: reproduce once and die.
• Iteroparity: reproduce repeatedly throughout life span.

Semelparity

• Reproduce once and die.
• Occurs more for organisms under variable environmental conditions.
• Favored when adult survival is low (lifespan < 1-2 years) or adult survival is high, but there are long intervals between years with conditions suitable for high offspring survival.
• Adults are able to dedicate all available resources to one reproductive event

Iteroparity

• Reproduce repeatedly throughout life span.

Agaves

• "Century plant" that inhabits climates with erratic rainfall
• Semelparous: reproduce during an unusually wet year (seeds have a higher chance of survival) and the parent plant dies after flowering (reproduction).

Salmon

• Exhibit a huge effort to migrate up rivers to reach spawning grounds.
• Semelparous: females convert a large portion of body tissue into eggs, reproduce, and die shortly after spawning.

Capelin

• Semelparous: males stay near the beach and spawn in multiple areas, then die.
• Iteroparous: females move in quickly, spawn once, and leave.