Biology 20 — Unit B

Ecosystems & Population Change

Ms. Terkper's Digital Classroom — Themes: Energy, Matter & Systems

Focusing Questions

"What are the major biotic and abiotic characteristics that distinguish aquatic and terrestrial ecosystems? What data would one need to collect in a field study to illustrate the major abiotic characteristics and diversity of organisms? What mechanisms are involved in the change of populations over time? In what ways do humans apply their knowledge of ecosystems to assess and limit the impact of human activities?"

General Outcomes

20-B1: Explain that the biosphere is composed of ecosystems, each with distinctive biotic and abiotic characteristics.

20-B2: Explain the mechanisms involved in the change of populations over time.

Key Concepts

EcosystemNicheBiotic FactorsAbiotic FactorsLimiting FactorsBinomial NomenclatureAdaptationPopulationNatural SelectionSpeciesSpeciationEvidence for Evolution

Unit Overview

Students become familiar with a range of ecosystems by studying their distinctive biotic and abiotic characteristics. Students are introduced to the concept of populations as a basic component of ecosystem structure and complete the unit by examining population change through the process of natural selection. This unit prepares students for the study of populations and community dynamics in Biology 30.

Builds on Prior Learning

Gr. 7 Interactions and Ecosystems, Gr. 8 Freshwater and Saltwater Systems, Gr. 9 Biological Diversity, and Bio 20 Unit A (Energy and Matter Exchange).

Ecosystem Organization & Characteristics

Ecological Hierarchy — Click a Level

Species

The most fundamental unit of classification

Population

All individuals of one species in an area

Community

All populations in an area interacting together

Ecosystem

Community plus all abiotic factors of the environment

Biotic Factors — Living Components

Biotic factors are all living organisms and their interactions within an ecosystem. They include:

Producers (Autotrophs)

Plants, algae, cyanobacteria
Convert solar/chemical energy to organic matter
Base of all food webs

Consumers (Heterotrophs)

Herbivores, carnivores, omnivores
Parasites, scavengers
Decomposers (bacteria, fungi)

Biotic interactions include: predation, competition, mutualism, commensalism, parasitism, and decomposition.

Abiotic Factors — Non-Living Components

Abiotic factors are non-living physical and chemical components that shape where organisms can live:

■ Temperature: Determines enzyme activity and metabolic rate
■ Sunlight: Energy source for photosynthesis; controls day length signals
■ Water / moisture: Universal solvent for biochemistry
■ Soil composition: Mineral nutrients, pH, texture, organic matter

■ Nutrients (N, P, K): Essential for growth; often limiting factors
■ Oxygen: Required for aerobic respiration; varies greatly in aquatic zones
■ pH: Affects chemical reactions and solubility of nutrients
■ Relative humidity: Controls water loss through transpiration

Limiting Factors — What Controls Where Organisms Can Live?

A limiting factor is any resource or condition that is present in amounts less than what an organism requires. The limiting factor prevents a population from growing beyond a certain size. Liebig's Law of the Minimum states that growth is controlled by the most scarce essential resource, not by the total amount of available resources.

Limiting Factor	Type	Effect on Organisms	Alberta Example
Temperature	Abiotic	Determines enzyme function, metabolic rate, dormancy triggers. Too hot or cold = death or migration.	Chinook winds cause rapid temperature swings in southern Alberta, stressing overwintering insects and plants
Water availability	Abiotic	Controls plant productivity; determines desert vs. grassland vs. forest	Annual precipitation gradient: <300 mm in SE prairies vs. >1,000 mm in Rocky Mountain valleys
Sunlight	Abiotic	Controls photosynthesis rate; creates vertical zonation in forests and water bodies	Boreal forest understory dominated by shade-tolerant mosses and ferns; canopy closure limits plant diversity below
Nutrients (N, P)	Abiotic	Limit primary productivity in terrestrial and aquatic systems	Nutrient-poor muskeg supports sparse spruce/tamarack; phosphorus limits algae growth in clear mountain lakes
Dissolved oxygen	Abiotic	Controls species composition in aquatic ecosystems; low O⊂2; = invertebrate/fish death	Ice cover in winter reduces O⊂2; in shallow lakes; some Alberta lakes experience winter fish kills
Competition	Biotic	Interspecific competition reduces resource availability for each species. Can lead to competitive exclusion.	Purple loosestrife outcompetes native cattails in Alberta wetlands by altering water retention
Predation	Biotic	Top-down control of prey populations; can prevent overgrazing	Wolf reintroduction in Banff controls elk populations, allowing willow/aspen regeneration
Parasitism	Biotic	Weakens host organisms; can cause population crashes at high infestation	Mountain pine beetle infestations in Alberta's Rocky Mountain lodgepole pine forests

Habitats, Niches & Ecosystem Zones

Habitat vs. Niche

The habitat is where an organism lives — its physical address. The ecological niche is the organism's complete role in the ecosystem — what it eats, when it is active, how it reproduces, what it competes with. The niche is the organism's "profession."

Competitive Exclusion Principle (Gause, 1934): No two species can occupy the same niche in the same place at the same time indefinitely. One species will always outcompete the other, leading to either competitive exclusion or niche partitioning (resource sharing by slightly different use).

Alberta example: Three species of warblers (Cape May, Bay-breasted, Myrtle) coexist in the same boreal spruce trees by foraging in different zones — top, middle and lower branches respectively. Same habitat, partitioned niches.

Fundamental vs. Realized Niche

Fundamental Niche

The full range of conditions and resources a species could theoretically use if there were no competitors or predators. Defined by physical tolerances (temperature, humidity, etc.).

Realized Niche

The actual conditions and resources a species uses in the presence of competition and predation. Always a subset of the fundamental niche. Biotic interactions shrink the realized niche.

Example: The American toad's fundamental niche includes all moist areas of Alberta. Its realized niche is smaller because it competes with the boreal toad for breeding ponds.

Ecosystem Zones Explorer

Taxonomy & Classification

Binomial Nomenclature

Developed by Carl Linnaeus (1753), binomial nomenclature gives every species a two-part Latin name: Genus species. This system is universal across all languages and cultures, allowing scientists worldwide to communicate precisely about organisms.

Rules of Binomial Nomenclature

Genus name is capitalized, species name is lowercase
Written in italics when typed; underlined when handwritten
Names are in Latin or Latinized Greek
Genus name may be abbreviated after first use (C. lupus after Canis lupus)

Alberta Examples

Common Name	Scientific Name
Grey wolf	Canis lupus
Bison	Bison bison
Black spruce	Picea mariana
Grizzly bear	Ursus arctos
Common loon	Gavia immer
Rocky Mountain elk	Cervus canadensis

Taxonomic Classification Hierarchy

The seven major classification levels, from broadest to most specific. Click a level below to see details.

Aboriginal Classification Systems

Alberta's First Nations, Métis and Inuit peoples developed detailed classification systems for the organisms in their territories — systems that parallel modern taxonomy and often capture ecological relationships that Western science formally recognized centuries later.

Blackfoot Plant Classification

Blackfoot people classified plants by their functional properties and ecological relationships: food plants, medicine plants, fiber plants, ceremonial plants, and indicator species. These categories reflect ecological niches — how and where the plants grow, what they interact with, and their role in the ecosystem. Buffalo berry (mî'skakatôminaan) and its relationship to bears was documented through oral classification long before scientific study.

Cree Animal Taxonomy

The Cree classification of animals grouped species by habitat, behavior and spiritual significance in ways that often aligned with modern biological groupings. Cree names frequently encoded ecological information — describing what the animal eats, where it lives, or how it behaves — making the name itself a classification statement. The Cree term amisk (beaver) carries embedded knowledge of the beaver's role as a water-environment modifier that ecologists now call "ecosystem engineering."

Métis & Woodland Cree Fungi Knowledge

Traditional knowledge includes detailed classification of edible, medicinal and toxic fungi — a classification that Western science did not formalize until the 19th century. Knowledge of which fungi grow in association with specific trees (mycorrhizal relationships) was embedded in harvesting practices: experienced harvesters knew that certain mushrooms only appeared under certain tree species, demonstrating an intuitive understanding of the ecological niche concept.

Variation, Heredity & Adaptation

Sources of Variation

Heritable mutations: Random changes in DNA sequence. Can be substitution, insertion, deletion, or chromosomal rearrangement. Most are neutral or harmful; occasionally a mutation increases survival/reproduction.

Sexual reproduction: Meiosis (crossing over, independent assortment) and random fertilization produce enormous genetic variation in offspring. No two sexually-produced offspring (except identical twins) are genetically identical.

Gene flow: Movement of individuals (and their alleles) between populations introduces new variation into a population.

Genetic drift: Random changes in allele frequency, especially significant in small populations. Founder effect and bottleneck effect are special cases.

Selective Advantage

A mutation has a selective advantage when it increases the organism's fitness — its ability to survive and reproduce in its environment. Selective advantage is always relative to the current environment. A mutation that is advantageous today may be neutral or harmful if the environment changes.

Types of Adaptations

Structural Adaptations

Physical body features that improve survival. Examples: thick fur of Arctic fox, hollow bones of birds, waxy cuticle of desert plants, counter-current circulation in fish gills.

Alberta example: Snowshoe hare's large hind feet distribute weight on snow; coat colour changes from brown to white in winter.

Physiological Adaptations

Internal biochemical processes that allow survival. Examples: antifreeze proteins in fish, nitrogen excretion as urea vs. uric acid, cold-resistant enzymes in alpine species.

Alberta example: Wood frog (Rana sylvatica) produces glucose antifreeze that prevents ice crystal formation in cells; survives being frozen solid in winter.

Behavioural Adaptations

Instinctive or learned behaviours that improve survival. Examples: migration, hibernation, flocking, alarm calls, caching food.

Alberta example: Clark's nutcracker caches thousands of whitebark pine seeds each autumn; spatial memory allows retrieval months later; critical to tree regeneration.

Natural Selection & Evolution

Lamarck vs Darwin — Two Explanations of Evolutionary Change

Jean-Baptiste Lamarck (1809) — Inheritance of Acquired Characteristics

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Core idea: Organisms change during their lifetime due to use or disuse of body parts; these acquired changes are passed to offspring.

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Giraffe example: Giraffes stretched their necks to reach higher leaves; longer necks were passed to offspring. Each generation stretched slightly more.

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Why it fails: There is no mechanism by which somatic (body) changes alter DNA in reproductive cells (Weismann barrier). A bodybuilder's muscles are not inherited.

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Historical importance: First major scientific theory of evolution. Proposed that species change over time — a radical idea in 1809. Shifted thinking away from fixed, unchanging species.

Charles Darwin (1859) — Natural Selection

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Core idea: Variation exists in populations. Individuals with advantageous traits survive and reproduce more. Advantageous traits become more common over generations.

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Giraffe example: Natural variation produced giraffes with different neck lengths. Those with longer necks reached more food, survived better, and reproduced more. Over generations, longer-necked giraffes became dominant.

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Why it works: Selection acts on existing heritable variation. The mechanism (DNA mutation, sexual reproduction) produces variation; the environment selects which variants reproduce.

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Key contributors: Wallace (parallel theory), Malthus (population pressure idea), Lyell (geological time), Buffon (species change concept).

Evidence for Evolution

Natural Selection Simulator

Allele Frequency Change Over Generations

Starting frequency of allele A (advantageous) 50%

Selective advantage of A 0.10

Number of generations 15

Allele A (advantageous)

Allele B

Four Conditions for Natural Selection

Variation exists in the population
Variation is heritable (passed to offspring)
More offspring are born than can survive (Malthus)
Traits affect survival/reproduction differently

Speciation

Allopatric speciation (most common): populations become geographically isolated. Genetic divergence accumulates. If isolated long enough, populations become reproductively incompatible — new species.
Alberta example: Columbian ground squirrels in isolated Rocky Mountain meadows show measurable genetic divergence between mountain valley populations.

Gradualism

Darwin's original model: evolution occurs through the slow, gradual accumulation of small changes over vast amounts of time. Species change continuously and imperceptibly generation to generation.

Consistent with observed microevolution in lab populations (bacteria, Drosophila)
Predicts many transitional fossil forms
Supported by Darwin's finch beak data (Peter and Rosemary Grant, 40+ years in Galapagos)
Slow environmental changes favour gradual adaptive shifts

Punctuated Equilibrium (Eldredge & Gould, 1972)

Evolution proceeds in bursts of rapid change separated by long periods of stasis (little change). Species remain stable for millions of years, then change quickly in geologically short intervals.

Explains the relative scarcity of transitional fossil forms
Rapid change usually follows extinction events or sudden environmental shifts
Cambrian Explosion (~540 mya) as evidence: rapid diversification after mass extinction
Burgess Shale (British Columbia, 508 mya): Exceptional fossil preservation showing the Cambrian burst of animal diversity — one of the world's most important fossil sites, and it's Canadian

Note: Gradualism and punctuated equilibrium are not mutually exclusive. Most biologists accept that both rates of change occur depending on conditions.

Past Mass Extinctions vs Current Species Decline

Event	Time (mya)	Species Lost (est.)	Primary Cause	Connection to Alberta
End-Ordovician	443	~86%	Glaciation, sea level drop	Marine invertebrate fossils in Alberta Rockies date from this era
Late Devonian	375–360	~75%	Ocean anoxia, climate cooling	Devonian coral reef fossil beds near Jasper National Park
Permian-Triassic (Great Dying)	252	~96%	Volcanic CO⊂2;, ocean acidification	Triassic strata in Alberta Foothills document the recovery period
End-Cretaceous (K-Pg)	66	~76%	Asteroid impact + volcanism	Dinosaur Provincial Park (UNESCO) contains one of the richest Cretaceous fossil beds on Earth
Current (Holocene) Extinction	~0.01 (ongoing)	1,000–10,000× background rate	Habitat destruction, climate change, overexploitation, invasive species	Woodland caribou, swift fox, burrowing owl, American badger all at-risk in Alberta

Human Impacts on Ecosystems & Biodiversity

Impact Categories

Habitat destruction & fragmentation: Roads, pipelines, and agricultural clearing divide continuous habitat into isolated patches. Reduces biodiversity, disrupts gene flow, increases edge effects. Over 70% of Alberta's native grasslands have been converted.

Wetland drainage: Alberta has lost over 65% of its original wetlands. Wetlands filter water, recharge groundwater, reduce flooding, and provide habitat for ~50% of Alberta's at-risk species.

Monoculturing: Growing a single crop/species eliminates natural biodiversity. Monoculture forests (single-species plantations) are far more vulnerable to disease and pest outbreaks than natural multi-species forests.

Interbasin water transfer: Moving water between river basins introduces invasive species, parasites (e.g., whirling disease), and alters flow regimes. Contentious in Alberta (North Saskatchewan to South Saskatchewan proposals).

Urbanization: Impervious surfaces increase runoff, reduce infiltration, create heat islands, and generate light/noise pollution that disrupts wildlife behaviour, migration and reproduction.

Invasive Species in Alberta — Click to Expand

Competitive Exclusion by Invasives

Invasive species often succeed because they enter an ecosystem without their natural predators, parasites and competitors. They occupy niches with reduced biotic resistance, allowing rapid population growth that outcompetes native species. Controlling invasives is one of the most costly environmental challenges in Alberta.

Land Reclamation — Science and Technology Responding to Environmental Damage

Alberta has strong land reclamation regulations requiring industrial disturbances (mines, oil sands, pipelines) to be restored to equivalent land capability. This is a major application of ecosystem biology in practice.

Oil Sands Reclamation

Alberta's oil sands operations must reclaim disturbed land to a "boreal forest equivalent." Reclamation involves reshaping terrain, rebuilding soil profiles, replanting native trees and shrubs, and re-establishing wetlands. As of 2023, only a small fraction of disturbed land has received certified reclamation.

Prairie Grassland Restoration

Converting cultivated land back to native prairie requires reseeding with original seed mixes (dozens of species), eliminating invasive weeds, and often re-introducing grazers (bison, cattle under managed programs) to simulate natural disturbance regimes.

Wetland Reconstruction

Ducks Unlimited Canada has restored or constructed over 570,000 ha of wetlands in Alberta. Wetland construction requires reshaping topography, establishing hydrology, and planting emergent vegetation. Restored wetlands recover most species diversity within 10–20 years.

Interactive Practice & Review

Knowledge Check Quiz

10 questions covering ecosystems, taxonomy, natural selection and evolution.

Bio 20 — Unit B

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Term Match

Match each concept on the left to its correct definition on the right.

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Vocabulary Flashcards

Click card to flip. Navigate all 20 terms.

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