Habitat and Ecological Niche

Habitat, Ecological Niche, and Ecological Equivalents

• Habitat refers to the physical location where a species lives, characterized by geographic, physical, chemical, and biotic factors.
• Environment encompasses all biotic and abiotic factors that surround and influence an organism and its habitat.
• The niche concept considers Joseph Grinnell's ideas regarding environmental influences.
• Charles Elton focused on biological interactions and abiotic factors.
• G.F. Gause studied interspecific competition.
• G. Evelyn Hutchinson described the n-dimensional hypervolume.

Ecological Niche

• Ecological niche is the role a species plays within an ecosystem, representing its lifestyle.
• The ecological niche can be defined by ranges of environmental conditions and resources necessary for survival.
• A fundamental niche is the full range of resources a species could use without competition.
• A realized niche is the actual resources or habitats a species uses in reality.
• The niche involves food sources, position in the food web, food acquisition methods, temperature range for survival, and reproduction.

Ecological Equivalents

• Ecological equivalents are species that occupy similar niches in different geographical locations.
• Ecological equivalents are unrelated organisms occupying similar habitats with similar appearances.

Natural vs Artificial Selection and Speciation

• Species are groups of organisms that interbreed to produce fertile offspring.
• Generalist species thrive in varied environments and consume diverse foods, like flies, rodents, and humans.
• Specialist species require specific habitats and tolerate limited conditions, such as koalas and giant pandas.
• Native/Endemic species live and thrive in a particular ecosystem.
• Exotic/alien/nonnative species are introduced into an ecosystem, often by humans.
• Indicator species provide early warnings of threats to a community.
• Keystone species have disproportionately important roles, and their loss can cause ecosystem collapse.

Evolution

• Evolution drives adaptation by changing a population's genetic makeup over generations.
• Microevolution involves small genetic changes.
• Macroevolution involves large-scale changes resulting in new species arising and others going extinct.
• Genetic variability containing DNA, genes, and alleles are the foundation for microevolution.
• Alleles of a shared trait are the basis of variation.
• Gene expression includes replication, transcription, and translation.

Microevolution - Four Processes

• Mutation involves changes in the genetic material of a cell, which can be caused by mutagens.
  • Mutations can be substitutions, insertions, deletions, or inversions.
• Gene flow involves the transfer of genes between populations through hybridization and migration
• Genetic drift describes random changes in allele frequencies.
  • The bottleneck effect is a reduction in population size due to natural disasters.
  • The founder effect is when a small group colonizes a new area.
• Natural selection is when traits enable better survival and reproduction, according to Alfred Wallace and Charles Darwin.
  • Variability of traits in a population is necessary.
  • Traits must be heritable.
  • Traits must lead to differential reproduction.
  • Adaptation is a heritable trait that helps survival and reproduction

Evolution by Natural Selection

• Selective pressure is a factor in the environment that drives natural selection.
• Evolution is changes over time.
  • Species accumulate differences.
  • Descendants differ from ancestors.
  • New species emerge from existing ones.
• Adaptation allows organisms to survive and reproduce.
  • Physiological adaptation includes antibiotic resistance.
  • Behavioral adaptation includes migration.
  • Structural adaptation includes mimicry and camouflage.
• Behavior is how organisms adjust to their surroundings.
  • Tropism is directed movement (phototropism, gravitropism, thigmotropism).
  • Taxes are stimulus response movements (chemotaxis, rheotaxis).
  • Reflexes involve specific body parts.
  • Instinct is encoded behavior (courtship, nest building).
  • Learning and reasoning.
• Acclimatization is adjusting to environmental changes, unlike adaptation which involves changes in gene pools.
• Artificial selection is selective breeding for desired traits.
• Speciation is the origin of new species through inherited variations.
  • Allopatric speciation occurs when populations are geographically isolated
  • Sympatric speciation occurs in the same geographic area.

Circadian Rhythms and Biological Clocks

• Circadian rhythms are daily physiological and behavioral cycles
  • Mechanisms include light/dark cycles.
  • Zeitgebers reset the circadian rhythm.
  • Photoperiod is the duration of light exposure.
• Photoperiodism is the physiological response to photoperiod (flowering, seed germination, bud dormancy).
• Biological clocks are endogenous, including the suprachiasmatic nucleus (SCN) in the hypothalamus and regulates the pineal gland which releases melatonin to regulate sleep patterns.
• Jet lag disrupts circadian rhythms due to crossing time zones.

Species Interactions

• Species interaction occurs when species share activities or resources in an ecosystem.
• Interspecific competition is amongst different species.
• Predation is when one species feeds on another.
• Symbiosis is a lasting, intimate association.
• Interference competition is when one species limits another's access to a resource.
• Exploitation competition is where species differ in resource exploitation efficiency.

Competitive Exclusion Principle

• No two species occupy the same niche competing for the same resources indefinitely ("one-niche, one-species, one-place").
• Resource partitioning is dividing scarce resources for species with similar needs.

Predation

• Porcupines have mechanical defenses.
• Skunks have chemical defenses.
• Poison dart frogs exhibit aposematic coloration or warning coloration.
• Canyon tree frogs have cryptic coloration or camouflage.

Mimicry types

• Batesian mimicry is when harmless species resemble poisonous ones.
• Mullerian mimicry is when poisonous species resemble each other.
• Crypsis involves concealing oneself.
• Symbiosis can be parasitism.
• Parasitoids infect hosts, and can be endoparasites or ectoparasites.
• Mutualism is when both species benefit
• Obligatory mutualism is when one cannot live without the other (e.g. lichen).
• Commensalism is when one species benefits and the other is unaffected.

Population Concepts

• A population is a group of interacting organisms of the same species in a space.
• Populations have gene flow, the ability to regulate growth, and social behaviors.
• Populations are characterized by distribution patterns, dispersal, density, and age structure.
• Density is the number of individuals per area.
• Dispersion is the spacing pattern of individuals.
  • Uniform dispersion caused when there are competitive interactions.
  • Random dispersion occurs without influence from others.
  • Clumped dispersion is when individuals occur in groups.
• Dispersal is movement from a birthplace to a new location.
  • Dispersal eases competition and reduces inbreeding.

Migration

• Migration is movement from one place to another (emigration: moving out, immigration: coming in).
• Population dynamics involves demography, population growth, natality (birth rate), and mortality (death rate).
• Survivorship is the percentage of individuals living at various ages.
• Survivorship Curve types:
  • Type 1 is a high survival rate early in life followed by mortality later in life.
  • Type 2 is a constant death rate.
  • Type 3 is a high mortality rate early followed by those that survive having a low rate of death.

Life Histories and Population Growth

• Life history is an organism's schedule of reproduction and survival.
  • It results from natural selection.
• Semelparity is reproduction occurring once (e.g., Agave, Octopus).
• Iteroparity is repeated reproduction.
• Population growth curves:
  • Exponential growth occurs without limits (J-shaped).
  • Logistic growth slows as it nears carrying capacity (S-shaped).
• K-selected species are sensitive to density, specialists, slow to mature and long-lived, invest heavily in offspring.
• R-selected species reproduce quickly, are generalists, mature rapidly and are short-lived and do not invest as much time in offspring.
• Density-dependent factors affect population size based on density, as biotic factors are at play.
• Density-independent factors affect population size regardless of density and involve abiotic factors.
  • Climatic factors include rainfall, drought, and temperature.
  • Anthropogenic factors include habitat destruction.
• Age structure reveals population trends.

Community Dynamics

• Community is assemblage of populations in space and time; the biological component of the ecosystem.
  • Species richness is the number of species present.
  • Relative abundance is the species amount.
• Collective and emergent properties of a community:
  • Collective properties are quantifiable features (e.g., biomass, diversity).
  • Emergent properties result from interactions (e.g., trophic structure).
• Community properties include global scale (vegetation and climate), finer scale, and biomes.
• Species diversity refers to the variety of taxa present.
• Diversity is measured by species richness and evenness of distribution.
  • Diversity decreases and abundance increases away from the equator.
  • Biodiversity includes variety of life forms.
• Species diversity is measured by the Shannon-Wiener Index (H).
  • A high H signifies high uncertainty
  • Index of evenness, with 1.0 meaning all species are equally represented
• Species diversity can also be measured by Simpson's Index.
• Species dominance is when dominant species influence the rest of the community.
• Keystone species exert strong community influence, and their removal causes ripple effects.
• Community structure involves the organization of components present like producers, consumers and decomposers
  • Trophic structure is determined by feeding relationships.
  • Food chains are linear energy flows through tropic levels.
  • Charles Elton created trophic levels.
• Life forms of organisms are classified by Raunkiaer's system based on meristem position.

Community Composition & Disturbances

• Vertical structure/stratification:
  • In terrestrial ecosystems, composition is based the canopy, etc.
  • In aquatic ecosystems, composition is based on light penetration or temperature.
• Zonation changes communities across a landscape.
  • Edges are where communities meet (inherent or induced).
  • Ecotones are where communities intergrade.
• Edge effect is when life is abundant at edges/ecotones, and is influenced by the amount of edge.
• Disturbances are events that alter a community.
  • Disturbances are also needed for community development and survival.
• Ecological succession is gradual change in community.
  • Seral stage/sere is each step in succession.
  • Succession is directional.
  • Climax community is self-regulating.
• Community persistence/resilience is the capacity to recover from a disturbance.
• Primary succession begins in lifeless areas.
• Secondary succession occurs after a community has been cleared and soil still remains.