ENVS 200: Introduction to Environmental Science

Course Overview

ENVS 200 Field Ecology at the University of Waterloo is an introductory course that uses ecology as its organizing lens. Ecology itself derives from the Greek oikos (“house”) and logos (“study of”), and at its core it is the scientific study of the distribution and abundance of organisms, the interactions that determine those patterns, and the relationships between organisms and the transformation of energy and matter through environments. A simpler framing comes from ecologist Robert Ricklefs: ecology is “the study of the natural environment, particularly the interrelations between organisms and their surroundings.” Either way, the field is defined by interconnection. As the first law of ecology holds — popularized by ecologist Garrett Hardin — “everything is connected to everything else,” and “we can never do merely one thing.”

The course is organized around a principle of ecoliteracy: the goal of becoming a citizen who can identify and explain the main principles of ecology, demonstrate how those principles apply to real-world situations including human–nature interactions, and analyze the elements of scientific inquiry as they pertain to ecological questions. The textbook used is Essentials of Ecology (4th edition) by Begon, Howarth, and Townsend. Laboratory work runs in parallel with lectures, offering hands-on field experience in local ecosystems including the University of Waterloo campus, Laurel Creek watershed, local woodlots, and wetlands.

Part I — The Science of Ecology

What Science Is (and Is Not)

Science is a process, not a fixed body of facts. Four hallmarks characterize scientific knowledge: it is empirical (grounded in observation and measurement rather than authority), skeptical (provisional and open to revision), reliable (reproducible across contexts and investigators), and dynamic (continuously refined as evidence accumulates). This last point is frequently misunderstood in popular discourse. When scientists speak of a “theory,” they do not mean a mere guess. A theory in science — capital T — is a well-supported explanatory framework that has survived the testing of many, many hypotheses. Evolutionary theory, for instance, is not one scientist’s conjecture; it is the synthesis of well over a century of corroborated evidence from genetics, paleontology, comparative anatomy, and ecology.

This means science does not provide proof in the mathematical sense. Instead, it tests competing explanations against evidence and adjusts confidence accordingly. A hypothesis that predicts observations well gains support; one that consistently fails to predict observations is revised or discarded. Natural history — careful descriptive observation of organisms and their environments — forms the foundation upon which experimental and analytical ecology are built. Description comes first; explanation follows.

The Scientific Method in Ecology

Ecological research follows the same general logic as any empirical science, but it faces distinctive challenges. Ecosystems involve organisms interacting with one another and with physical environments across scales ranging from soil microbes to global biogeochemical cycles. Controlled laboratory experiments are sometimes possible, but field ecology often requires observational and quasi-experimental designs.

The cycle of inquiry begins with observation: noticing a pattern or phenomenon in nature. From observation, a researcher develops a hypothesis — a testable statement about what is causing or explaining the pattern. A well-formed hypothesis must be falsifiable: there must be some possible result that could contradict it. For example, noticing that roadside vegetation appears stunted near winter-salted roads might lead to the hypothesis: “Salt applied to roads in winter affects the growth of plants along the road.” This is testable either by observing plants along salted versus unsalted roads, or by designing a controlled experiment comparing growth under both conditions.

A critical companion to the working hypothesis is the null hypothesis: a statement that there is no significant difference or effect. For the road salt example, the null hypothesis would be “Salt applied to roads in winter has no effect on the growth of plants along the road.” Statistical testing in ecology generally works by asking how likely the observed data would be if the null hypothesis were true. If that probability is very low (conventionally, p < 0.05), the null hypothesis is rejected.

Hypotheses must be tractable. A hypothesis like “a significant change in plant growth along highways over the past 50 years has occurred due to road salt” is far harder to test — it would require historical data spanning five decades and would be confounded by the many other variables (land use, climate, pollution) that have changed over that period. Good scientific questions are focused and answerable with available methods and data.

Data Collection and Statistical Reasoning

After formulating a hypothesis, researchers design a study and collect data. Key principles include replication (measuring multiple individuals or plots, not just one), careful documentation of methods (so others can repeat the work), and attention to potential sources of bias or confounding variables (other factors that could explain the observed pattern).

Data are rarely self-explanatory. Raw measurements must be summarized, and the appropriate summary depends on the question. In a study comparing plant heights on salted versus unsalted roads, presenting the raw height of every individual plant would obscure the pattern; calculating a mean with some measure of variation (such as standard deviation or standard error) allows comparison across groups. Figures and tables in scientific papers are not decorations — they are the principal vehicle for communicating quantitative patterns. A good figure includes a title, clearly labeled axes, a legend, and (for maps) a scale bar, north arrow, and the geographic locations of study sites.

Statistical significance — indicated by a p-value below a chosen threshold — tells you that an observed difference is unlikely to have arisen by chance. However, statistical significance does not by itself tell you whether the difference is ecologically meaningful. A very large sample can make a tiny, biologically trivial difference statistically significant. Good ecological thinking requires integrating statistical results with biological reasoning.

Part II — Scientific Writing

Why Scientific Communication Matters

Ecology, like all science, is a cumulative and collaborative enterprise. Every study builds on the work that preceded it and creates the foundation for work that will follow. This makes effective communication not a peripheral skill but a central one. Research that cannot be clearly communicated to others — whether in methods, results, or interpretation — cannot be incorporated into the broader body of knowledge.

Scientific journal articles are the primary medium through which ecological findings are disseminated. They serve three interrelated purposes: they disseminate new findings including methods, results, and discussion; they suggest implications and possible applications of known and new findings; and they develop new questions to be addressed in future research. Every section of a scientific article is designed to serve one or more of these purposes.

Structure of a Scientific Article

Most ecological journals require the same core sections, though the exact format (e.g., word limits, heading styles, citation format) varies by journal. These sections are:

Abstract · Keywords · Introduction · Methods · Results · Discussion · References

Each section has a distinct function, and writing all of them well requires understanding those functions deeply.

The Abstract

The abstract is the first section a reader encounters and, practically speaking, the only section most readers will read in full. Despite its brevity, it is one of the most demanding sections to write. A good abstract provides a concise summary of the entire article: why the study was conducted (context and hypothesis), how it was conducted (brief methods), what was found (key results), and what those findings mean (main conclusions). Because it synthesizes all sections, the abstract is conventionally written last, even though it appears first. Abstracts typically run 150–300 words in ecology journals.

Keywords

Keywords are placed directly after the abstract and serve an indexing function: they allow other researchers to find the paper through database searches. Good keywords are concepts, methods, organisms, or theories central to the paper’s content — not generic terms like “plants” or “roads” that would return thousands of irrelevant results, but more specific phrases like “road salt,” “winter road maintenance,” and “salt damage to vegetation.” Keywords should reflect what distinguishes the paper from others in the broader literature.

The Introduction

The introduction follows a characteristic funnel structure: it opens broadly and narrows progressively toward the specific study. A well-written introduction accomplishes four things: it provides general background on the problem; it introduces the study’s context and explains why the work is needed; it clearly states the hypothesis (and often the null hypothesis); and it briefly introduces the study location and the general approach to testing the hypothesis.

Think of the introduction as a narrative that guides the reader from the general landscape of the problem to the specific doorway of the study. For the road salt example, one might open with the broad environmental consequences of winter road maintenance, then narrow to evidence of plant damage in Ontario, and finally arrive at the specific study sites in Waterloo Region. Each sentence builds on the previous one, progressively focusing the reader’s attention.

References are used extensively in the introduction to situate the study within existing knowledge. There is rarely a hypothesis worth testing that has no prior literature. Citing that literature serves two functions: it gives credit to prior work, and it demonstrates that the study fills a genuine gap or extends previous knowledge in a meaningful way.

The Methods

The methods section answers a simple but demanding question: could someone else replicate this study? It describes the study location, the equipment used, the field and laboratory procedures followed, and how data were analyzed. Maps of study locations — showing the geographic context, sampling sites, scale, and north arrow — are standard components of ecological methods sections. Every methodological choice should be described with enough precision that the reader can evaluate its appropriateness and, if needed, reproduce the work.

The methods section is also the foundation for interpreting results. A reader who cannot understand how data were collected cannot properly evaluate what those data mean. Methods are typically written in the past tense and passive voice (e.g., “Three plants were randomly selected at each site”) because the focus is on what was done, not on the investigator doing it.

The Results

The results section presents what was found, without interpretation or opinion. It is organized to guide the reader through the findings in a logical order — not simply as a list, but as a narrative that highlights key patterns. Text in the results identifies and describes trends; figures (graphs, maps, photographs) and tables display large amounts of data concisely so that patterns are visually apparent.

An important distinction: the results section reports data as they pertain to the hypothesis. Tangential findings — interesting as they might be — belong either in a footnote or in a future study. The discipline of staying focused on what was hypothesized is one of the hallmarks of good scientific writing. Results are never described with phrases like “this proves the hypothesis” — science does not prove; it supports or fails to support.

Data should be presented in summary form. Displaying every raw measurement obscures rather than reveals patterns. For a study with three sampling sites per road type and three plants per site, the most informative presentation is a table showing the mean (and ideally a measure of variability) for each road type, not a table of 18 individual measurements.

The Discussion

The discussion is often the most intellectually demanding section and the one where the writer’s understanding of the science is most visible. Its structure is roughly the inverse of the introduction: it begins with the specific findings of the study, then situates those findings in the broader context of the relevant literature, and ends with the broad implications of the work.

The discussion serves six interrelated functions. First, it interprets the data: what do the numbers actually mean? Second, it assesses support for the hypothesis: do the findings support the original prediction, fail to support it, or yield a mixed picture? (Remember — results “support” or “fail to support” a hypothesis; they do not “prove” or “disprove” it.) Third, the discussion compares findings to prior work: does this study agree with similar research? If not, why might there be discrepancies (different species, different climates, different concentrations of the variable being studied)? Fourth, it acknowledges limitations: every study has them, and they must be stated, not apologized for. Common limitations in ecological work include restricted sample sizes due to logistical constraints, geographically specific study sites that limit generalizability, and incomplete data collection due to weather or seasonal constraints. Crucially, the discussion must explain how those limitations might affect the interpretation of results — simply listing them is insufficient. Fifth, the discussion states a broad conclusion that the study contributes to. And sixth, it suggests future directions that flow naturally from the current findings.

One of the most common errors in discussion writing is including personal opinions. Scientific writing is not the place for statements like “salt is obviously a very bad chemical and we should stop using it.” Such language reveals advocacy rather than analysis. Recommendations for action, if included at all, should be grounded in evidence, qualified appropriately, and distinguished from the scientific findings themselves. Similarly, claims should be supported by citations. Stating that “salt has been shown to have deleterious effects on plants” without citing the studies that showed it is an unsubstantiated assertion.

Citations and Peer Review

The reference list is not a formality — it is a map of the intellectual landscape in which the study was conducted. APA format is used in ENVS 200. The basic tenets of citation practice are simple: cite any non-original ideas that do not qualify as common knowledge; paraphrase rather than directly quote (direct quotes must be in quotation marks); and list every source cited at the end of the article in the reference list. Citations appear where needed across the paper — heavily in the introduction and discussion, possibly in the methods if describing established protocols, and rarely (or never) in the abstract and results.

A crucial distinction in scientific writing is between peer-reviewed and non-peer-reviewed sources. Peer review is the process by which a submitted manuscript is evaluated by independent experts in the field before publication. Reviewers assess the methodological rigor, the validity of conclusions, and the significance of the findings. Peer review does not guarantee that a published paper is correct — reviewers miss things, methods have flaws, and results sometimes fail to replicate — but it substantially raises the quality threshold compared to non-reviewed sources. When conducting ecological research, peer-reviewed journal articles (accessible through the UW library and platforms like Google Scholar) are the primary scholarly currency.

Part III — Introduction to Ecology

The Scope of Ecology: Scale and Hierarchy

Ecology is not a single-scale discipline. Ecologists work across a nested hierarchy of biological organization, from individual organisms — their physiology, behavior, and responses to environmental conditions — up through populations (groups of individuals of the same species in a defined area), communities (assemblages of populations of different species interacting in the same area), ecosystems (communities plus their abiotic environment, linked by flows of energy and matter), and the biosphere (the sum of all ecosystems on Earth). Understanding ecological patterns often requires moving between these scales simultaneously: a population trend may only make sense in the context of the community’s predator–prey dynamics, which in turn depend on ecosystem-level nutrient availability.

The Pope’s 2015 encyclical Laudato Si’ — an unusual but apt reference — captures this multi-scale reality: “Ecology studies the relationship between living organisms and the environment in which they develop. It cannot be emphasized enough how everything is interconnected.” This interconnectedness is both an empirical observation and a philosophical orientation that shapes how ecological questions are framed.

Organisms and Their Environments

Every organism exists within a set of conditions (abiotic factors that affect physiology, such as temperature, pH, and light) and resources (things consumed by organisms, such as nutrients, water, and food). The range of conditions and resources within which an organism can survive and reproduce defines its ecological niche — classically conceptualized as an n-dimensional hypervolume in which each dimension represents one environmental variable. The fundamental niche is the full range the organism could theoretically occupy; the realized niche is the subset actually occupied once the effects of competitors, predators, and other species are taken into account.

Organisms respond to environmental gradients through response curves: graphical representations of performance (growth, survival, reproduction) as a function of a single environmental variable. Most response curves are unimodal — performance is highest at an intermediate value and declines toward both extremes. Organisms have evolved a remarkable variety of strategies for dealing with conditions at the extremes of their tolerance: avoiders evade harsh conditions through migration, dormancy, or microhabitat selection; tolerators possess physiological or biochemical adaptations (such as antifreeze proteins or heat-shock proteins) that allow survival under extreme conditions.

Ectotherms — organisms whose body temperature is determined primarily by the external environment — include most invertebrates, fish, amphibians, and reptiles. Their metabolic rates and activity levels vary strongly with ambient temperature. Endotherms — birds and mammals — maintain a relatively constant internal temperature through metabolic heat production, allowing activity across a broader range of external temperatures but at considerably higher energetic cost.

The Human Footprint: Anthropogenic Biomes

One of the most important insights of modern ecology is that there are few, if any, truly wild places remaining on Earth. Ecologist Erle Ellis and colleagues have proposed the concept of anthropogenic biomes — a reclassification of Earth’s land surface based not on climatic and vegetation zones (the traditional biome concept) but on the actual human footprint. Dense settlements, villages, irrigated croplands, rangelands, populated forests, and remote wildlands now constitute the dominant categories of land cover on the planet. This framing does not diminish the importance of remaining wild areas; it does underscore that ecological understanding cannot proceed as if human activity were a marginal overlay on an otherwise pristine natural world. We are embedded within the systems we study.

Part IV — Biodiversity I: Concepts, Measurement, and Importance

What Is Biodiversity?

Biodiversity — a contraction of “biological diversity” — refers to the variety of life on Earth and the ecological processes that sustain it. It operates at three nested levels. Genetic diversity is the variation in genetic information within and among populations of the same species; it is the raw material of evolution and provides the adaptive potential that allows populations to respond to environmental change. Species diversity is the variety of species in a given area — the level most commonly invoked in everyday discussion, and the focus of most ecological measurement. Ecosystem diversity encompasses the variety of habitats, communities, and ecological processes across the landscape; it includes not just which species are present but how they interact and how energy and matter flow between them.

Conservation biologist Edward O. Wilson estimated that Earth harbors somewhere between 5 and 100 million species, of which fewer than 2 million have been formally described and named. This extraordinary cataloguing gap means that species are going extinct faster than science can discover them — a sobering reality that underscores the urgency of biodiversity research.

Species Richness and Evenness

The simplest measure of species diversity is species richness (S): a count of the number of distinct species in a defined area or sample. Richness is intuitive and easy to communicate, but it is an incomplete picture. Consider two forest plots, each containing four species. In the first plot, one species makes up 97% of all individual trees and the other three together account for 3%. In the second plot, each species contributes approximately 25% of individuals. Both plots have the same species richness, but they are ecologically very different communities.

This is where evenness becomes essential. Evenness measures how equitably the total abundance (or biomass, or energy) is distributed among species. An evenness value of 1 indicates perfect equality — every species is equally common. An evenness value near 0 indicates extreme dominance by one or a few species. A community with high richness and low evenness can, in some respects, be less diverse than a community with moderate richness and high evenness.

Diversity Indices

To combine richness and evenness into a single metric, ecologists use diversity indices. The two most widely used are the Shannon diversity index and the Simpson diversity index.

The Shannon diversity index (H’) is borrowed from information theory, where it quantifies the uncertainty of predicting the identity of a randomly selected individual from a community. It is calculated as:

H’ = −Σ (pᵢ × ln pᵢ)

where pᵢ is the proportion of individuals belonging to species i, and the sum is taken over all species present. H’ increases as both richness and evenness increase. A community with many species of equal abundance has the highest H’ for its richness; a community dominated by one species has an H’ approaching 0. In practice, most ecological communities have H’ values between 1.5 and 3.5, though values outside this range occur.

The Simpson diversity index (D) quantifies the probability that two randomly selected individuals from a community belong to different species. It is often expressed in its complement form (1 − D) or as an inverse (1/D) to make it positively correlated with diversity. The raw Simpson index is:

D = Σ pᵢ²

A high D means the community is dominated by a few species (you have a high probability of picking the same species twice); therefore, the complement (1 − D) or the reciprocal (1/D) are more interpretively intuitive.

These indices, while powerful, are abstractions. They reduce rich biological information to a single number, which inevitably entails trade-offs and assumptions. They are most useful when comparing communities with one another or tracking change in diversity over time, rather than as standalone measures of ecological health.

Species evenness is often calculated separately from richness using Pielou’s J statistic:

J = H’ / H’max = H’ / ln(S)

where H’max = ln(S) is the maximum possible Shannon index for a community with S species (achieved when all species are equally abundant). J ranges from 0 to 1.

Alpha, Beta, and Gamma Diversity

Diversity can be measured at multiple spatial scales, and ecologists distinguish three conceptual levels. Alpha diversity (α-diversity) is the diversity within a single site or habitat — what most people mean by “local diversity.” Beta diversity (β-diversity) quantifies the turnover in species composition between sites: how different are two communities from each other? High beta diversity means many species are restricted to particular habitats, so protecting one site captures relatively little of the total regional biodiversity. Gamma diversity (γ-diversity) is the total diversity across an entire landscape or region — the union of all species found across all sites. The relationship γ = α × β (conceptually, though the exact formulation depends on the metric used) shows that regional diversity is a product of both local richness and turnover among sites.

Understanding these scales is crucial for conservation planning. Protecting a few large areas with high alpha diversity does not substitute for a network of areas distributed across habitats if beta diversity is high.

Gradients and Patterns of Species Richness

Species richness is not randomly distributed across the planet. Several robust macroecological patterns have been documented.

The latitudinal diversity gradient — the tendency for species richness to be highest near the equator and to decline toward the poles — is one of ecology’s oldest and most reliably documented patterns. It holds across most taxonomic groups and most continents. The causes remain debated; leading hypotheses invoke greater energy availability in the tropics (the energy hypothesis: more solar energy supports more productivity, which can support more species), longer evolutionary history with fewer mass extinctions in tropical refugia, higher rates of speciation in the tropics, and the greater stability of tropical climates over geological time.

The species-area relationship describes the tendency for larger areas to contain more species, typically following a power-law curve: S = cA^z, where S is species richness, A is area, c is a constant, and z is typically around 0.25–0.35 for biogeographic regions. This relationship has profound conservation implications — habitat loss does not eliminate species in direct proportion, but it does reduce species numbers, and very small habitat fragments often cannot sustain viable populations of area-sensitive species.

The intermediate disturbance hypothesis (IDH), developed by Joseph Connell, proposes that species diversity is maximized at intermediate levels of physical disturbance. At low disturbance, competitive exclusion — the tendency for the best competitor to eliminate weaker ones — reduces diversity. At high disturbance, only the most disturbance-tolerant species survive. At intermediate levels, disturbance prevents any single species from achieving competitive dominance, allowing more species to coexist. The IDH has had enormous influence on conservation and management thinking, though its generality has been questioned and empirical support is mixed in some systems.

The Role of Productivity

The productivity hypothesis proposes that species richness increases with primary productivity — that more energy-rich environments support more species. The relationship is not always monotonic; in some systems (particularly grasslands), very high productivity reduces richness because a few fast-growing species outcompete the rest. This unimodal relationship — low diversity at both very low and very high productivity — is one of the most studied patterns in community ecology and remains actively contested. Eutrophication, the enrichment of aquatic systems with nitrogen and phosphorus (often from agricultural runoff and sewage), provides a real-world demonstration of the diversity-reducing effects of excess productivity: the algal blooms that follow nutrient loading shade out other aquatic plants, deplete oxygen (causing the paradox of enrichment), and ultimately simplify the community.

Biodiversity and Ecosystem Function

Why does biodiversity matter beyond its intrinsic value? Decades of experimental and observational work have established that biodiversity and ecosystem function are linked, though the mechanisms and the generality of the relationship continue to be studied. Higher species diversity tends to increase ecosystem productivity (the total amount of biomass produced), stability (the tendency to maintain function in the face of perturbations), and resistance to invasion by non-native species. The mechanisms include niche complementarity — diverse communities use available resources more completely — and sampling effects — communities with more species are more likely to include highly productive species.

Classification and Naming of Organisms

Ecologists need a shared, stable vocabulary for referring to organisms. The Linnaean classification system assigns each species a unique binomial name (a practice called binomial nomenclature): a genus name and a species epithet, both in Latin or latinized Greek, italicized in text (e.g., Branta canadensis for the Canada Goose). Classification is hierarchical: Kingdom → Phylum/Division → Class → Order → Family → Genus → Species (and with subspecies and variety below that). This hierarchy is meant to reflect evolutionary history — closely related organisms should be classified near one another — though our understanding of evolutionary relationships continues to be revised as molecular genetic tools produce new phylogenetic evidence.

The concept of “species” itself is surprisingly contentious. The most widely used definition is the Biological Species Concept: a species is a group of organisms that can potentially interbreed in nature to produce fertile offspring and are reproductively isolated from other such groups. Pre-zygotic isolation prevents the formation of hybrid offspring (through differences in timing of reproduction, habitat use, courtship behavior, or incompatible reproductive structures); post-zygotic isolation reduces the fitness of hybrid offspring even when they form (hybrids may be inviable, sterile, or otherwise reproductively disadvantaged). The Biological Species Concept works well for sexually reproducing animals but poorly for bacteria, many plants (which hybridize extensively), and extinct organisms known only from fossils.

The taxonomy of organisms — the science of naming, classifying, and describing — is a fundamental backbone of ecology. You cannot study the distribution of a species, its ecological role, or its conservation status without knowing which species you are talking about. Lab work in ENVS 200 includes practice in species identification using field guides and dichotomous keys, with a focus on local Ontario flora and fauna.

Native, Exotic, and Invasive Species

Not all species in a given location arrived there through natural processes. A native species is one that existed in an area prior to European settlement. In Ontario, this designation is nuanced: a species can be native to the province but not to a particular ecological zone within it (e.g., a species native to the Carolinian zone in southwestern Ontario is not necessarily native to the Boreal zone of the north).

An exotic species (also called non-native, alien, or introduced) is one that has been established in an area through human activity, either deliberately (introduced for agriculture, horticulture, or biological control) or inadvertently (stowaways in cargo, ballast water, or soil). Most exotic species fail to establish persistent populations; a small fraction become invasive species, spreading aggressively and causing ecological or economic harm. Invasive species succeed in part because they leave behind the natural enemies — predators, pathogens, herbivores — that regulated their populations in their native range. European buckthorn (Rhamnus cathartica), for example, is an invasive shrub in Ontario’s forest edges and riparian zones, notorious for re-sprouting vigorously after cutting. Its management illustrates the challenge of controlling invasive species: different removal methods (complete root removal, cutting only, cutting plus herbicide application) differ in both effectiveness and efficiency, and the best approach often depends on context.

Naturalized gardens represent a strategy for restoring some of the ecological functions of native plant communities in urban settings. By modeling plantings after local natural communities — sunny meadow gardens, woodland understory gardens — naturalized gardens support native pollinators, birds, and other wildlife that depend on native plants, while reducing the inputs (water, fertilizer, pesticides) required by conventional urban lawns.

Citizen Science and iNaturalist

Biodiversity monitoring at large scales requires more observers than professional scientists can provide. Citizen science — the engagement of non-professional volunteers in systematic data collection — has become an increasingly important component of ecological research. The iNaturalist platform allows users to upload geotagged photographs of organisms, which are then identified by the community and verified by expert reviewers. The resulting database contains tens of millions of observations of hundreds of thousands of species worldwide, providing spatially extensive occurrence data that would be impossible to gather through traditional survey methods alone.

iNaturalist observations contribute to our understanding of species distributions, phenology (the timing of seasonal events), and the spread of invasive species. They also function as a tool for biodiversity education, encouraging careful observation of the natural world and familiarity with local species. In ENVS 200, students use iNaturalist to record wildlife observations on and around the University of Waterloo campus — documenting mammals, birds, plants, lichens, fungi, and invertebrates — as part of the first lab exercise.

Part V — Field Methods and Lab Safety

Ecological Field Methods

Ecological fieldwork relies on a toolkit of methods adapted to different questions and organisms. Understanding these methods — their assumptions, their strengths, and their limitations — is as important as understanding the biological concepts they are used to investigate.

Transects are survey lines along which observations are recorded at fixed intervals or within fixed-width strips. They are commonly used to document species occurrence, abundance, and habitat associations along environmental gradients. Quadrats — rectangular or square plots of defined area — are used to count or measure organisms in a standardized way, allowing density and cover estimates to be extrapolated to larger areas. Mark-recapture methods estimate population size by capturing individuals, marking them (with paint, tags, or other non-harmful identifiers), releasing them, and then recapturing a second sample: the proportion of marked individuals in the second sample gives an estimate of total population size.

Basal area — the cross-sectional area of a tree stem at breast height (1.3 m above ground, or DBH = diameter at breast height) — is a standard metric in forest ecology. It integrates both the number of stems and their size, providing a measure of the “bulk” of each species in the stand. Relative abundance, density, dominance, and basal area can be combined into an importance value that reflects each species’ overall ecological role in the community.

Density of trees in a woodland plot can be estimated using the point-quarter method: at each sampling point, the nearest tree in each of four quadrants (90° sectors around the point) is identified and its distance measured. The average distance and the known area then allow density to be estimated.

Succession

Succession is the process by which one ecological community replaces another over time, eventually arriving at a relatively stable climax community in dynamic equilibrium with the local environment. Primary succession begins on surfaces that have never been colonized — bare rock exposed by a retreating glacier, a new volcanic island — and may take centuries to develop a mature soil and forest community. Secondary succession begins after an incomplete disturbance of an existing community — a forest fire, a windthrow gap, an abandoned agricultural field — and proceeds more rapidly because soil, seed banks, and root systems may partially persist.

Succession is not a deterministic march toward a single endpoint. The pathway of succession depends on the priority effect (which species arrive first and establish before others), the nature of the disturbance (fire versus flooding versus wind create different starting conditions), and the regional species pool. In mid-successional stages, species richness tends to be high because early-successional and mid-successional species coexist; in late succession, competitive exclusion by a few dominant canopy species may reduce richness. In urban woodlots, succession is complicated by ongoing disturbances (fragmentation, invasive species, altered hydrology) that may arrest or divert successional trajectories.

The edge effect describes the tendency for species diversity and organism density to be elevated at the boundary between two ecological communities (the ecotone). Edge habitats support species of both adjacent communities as well as species specifically adapted to edge conditions (edge species). However, edges also expose interior-forest species to predators, parasites, and invasive species at higher rates, so the net effect of increasing edge on biodiversity is context-dependent.

Stream Ecology

Running-water (lotic) and standing-water (lentic) ecosystems differ fundamentally in their physical structure and the organisms they support. Lotic systems are characterized by directional flow that transports suspended materials, high oxygen content (generated through turbulence at riffles), and organisms adapted to resist or avoid current — often flattened body forms, suction cups, or behavioral flow-seeking. Lentic systems show vertical stratification of temperature, light, and oxygen; suspended materials settle out; and the biota respond to gradients of light and nutrients.

Watersheds (also called catchments or drainage basins) are the land areas that funnel precipitation and snowmelt into a river system. Everything that happens on a watershed — land use, urbanization, agriculture, atmospheric deposition — ultimately affects the stream at its center. The riparian zone, the transitional area between aquatic and terrestrial systems along a stream bank, is ecologically disproportionately important: it filters runoff, provides habitat, supplies organic matter to the stream as leaf litter, and moderates stream temperature through shading. Eutrophication — the enrichment of a water body with nitrogen and phosphorus — accelerates in urbanized and agricultural watersheds, where nutrient loading from fertilizer, sewage, and stormwater drives algal blooms, oxygen depletion, and community simplification.

Benthic invertebrates — bottom-dwelling animals without backbones — are widely used as indicator species of stream water quality. Their value as bioindicators derives from several properties: they are relatively sedentary (so they integrate conditions at the local site over weeks to months), they include species with varying tolerances for pollution, and they are diverse and abundant enough to allow community-level analyses. Sensitive taxa (stonefly larvae, mayfly larvae, caddisfly larvae) occur only in clean, well-oxygenated water; tolerant taxa (midge larvae, tubifex worms) dominate in degraded conditions. The ratio of sensitive to tolerant taxa provides a rapid, inexpensive index of stream health.

Dissolved oxygen (DO) concentration in water depends on temperature, salinity, and turbulence. Cold water holds more dissolved gas than warm water; high biological oxygen demand (from decomposition of organic matter) depletes DO. Salmonids and stoneflies require high DO (typically > 7 mg/L); warm-water fish like carp and catfish tolerate much lower concentrations. pH affects the solubility of metals (lower pH mobilizes toxic aluminum from soils) and the activity of microorganisms; most stream macroinvertebrates are sensitive to acidification.

Wetlands

Wetlands — transitional ecosystems between fully terrestrial and fully aquatic systems — are among the most ecologically productive and threatened habitats on Earth. Ontario’s wetland classification distinguishes marshes (dominated by emergent herbaceous vegetation like cattails and bulrushes, with water at or above the soil surface), swamps (dominated by woody vegetation — trees or shrubs — with seasonally or permanently flooded soils), fens (peat-forming wetlands with groundwater seepage, less acidic than bogs, often dominated by sedges and tamarack), and bogs (peat-forming, precipitation-fed, highly acidic, dominated by sphagnum mosses and acid-loving ericaceous plants). The lagg is the sharp ecotonal zone between the acidic peat of a bog and the surrounding mineral soil, representing an abrupt chemical and biological transition.

Wetlands perform critical ecosystem services: they store carbon as peat (making them net carbon sinks that help moderate climate), filter nutrients and contaminants from groundwater and surface water, recharge aquifers, buffer against flooding by absorbing runoff, and provide habitat for a disproportionately high fraction of biodiversity — including numerous species listed as at-risk in Ontario and Canada.

Field Safety

Effective ecological fieldwork requires not only scientific skill but also situational awareness and preparation for physical hazards. Several risks are particularly relevant to field ecology in southern Ontario.

Heat stress becomes significant during warm-season fieldwork. Both water-depletion heat exhaustion (characterized by thirst, weakness, and headache) and salt-depletion heat exhaustion (characterized by muscle cramps and dizziness) can progress to life-threatening heat stroke if untreated. Prevention requires regular hydration even before thirst develops, light and loose-fitting clothing, sun protection (hat and sunscreen), and monitoring of the heat index — the combined effect of temperature and humidity on perceived heat.

Ticks — particularly the blacklegged tick (Ixodes scapularis), the vector of Lyme disease — are prevalent in brushy and grassy habitats across southern Ontario. Ticks are sometimes as small as a poppy seed and difficult to spot on skin or clothing. They begin burrowing into the skin after approximately 24 hours of attachment, so post-fieldwork tick checks are essential. Lyme disease typically manifests one to four weeks after a bite with flu-like symptoms (fever, headache, muscle and joint pain, fatigue) and, in about 70–80% of cases, the characteristic bull’s-eye rash at the bite site. Prompt tick removal with fine-tipped tweezers — grasping as close to the skin as possible and pulling straight out, without squeezing — and preservation of the removed tick for testing can reduce transmission risk and facilitate diagnosis.

Mosquitoes can transmit West Nile virus, though serious illness in humans is relatively rare. Wasps and bees may sting when disturbed; allergic reactions (anaphylaxis) can be life-threatening and require immediate emergency response. Poison ivy (Toxicodendron radicans) is recognizable by its trifoliate leaf arrangement (the terminal leaflet on a longer stalk, flanked by two sessile lateral leaflets) and causes a severe contact dermatitis in most people through the oily resin urushiol; avoidance and protective clothing are the best strategies.

Lightning poses serious risk during summer thunderstorms. The 30-30 rule provides a practical guideline: if the interval between a lightning flash and its associated thunder is less than 30 seconds, seek shelter immediately and do not resume outdoor activity until 30 minutes after the last lightning is observed. When caught in the open, avoid high ground, isolated tall objects, and metal — and spread out from others to reduce the risk that a single strike affects multiple people.

Water safety deserves particular attention in stream ecology fieldwork. Bank stability, water depth, current velocity, and turbidity may all be difficult to assess visually. Clay banks erode and slump; fast, murky water obscures depth; even shallow but fast-flowing water can knock a person off their feet. No ecological measurement is worth a safety risk.

Part VI — Threats to Biodiversity

The Biodiversity Crisis

The current rate of species extinction is estimated to be 100–1,000 times higher than the background rate observed in the fossil record — a pace that many biologists characterize as the sixth mass extinction event in Earth’s history. Unlike the previous five, this one is driven by a single species: Homo sapiens. The proximate causes are well-documented and interacting.

Habitat loss and fragmentation is the leading cause of species extinction globally. As habitats are cleared, degraded, or divided into isolated fragments, populations lose the area, connectivity, and resources they require. Smaller populations are more vulnerable to demographic uncertainty (random variation in birth and death rates), environmental uncertainty (unpredictable events like drought or disease), and genetic erosion (loss of allelic diversity through inbreeding and genetic drift). The extinction vortex describes the self-reinforcing feedback: small populations decline in size, which increases inbreeding, which reduces fitness and fecundity, which further shrinks the population. Once a population enters the vortex, it is difficult to reverse.

Overexploitation — harvesting species faster than they can reproduce — drove the historic decline of many large vertebrates (bison, passenger pigeon, Atlantic cod) and continues to threaten fish stocks, large predators, and species harvested for traditional medicine, the pet trade, and luxury markets. The concept of maximum sustainable yield (MSY) attempts to identify the harvest rate at which a population can be removed without long-term decline. In practice, MSY is difficult to estimate reliably and politically difficult to enforce.

Introduced and invasive species represent the second leading cause of extinction for animals and a major cause for plants. Invasive species alter community structure through predation (introduced cats and rats have devastated island bird populations), competition, disease (chestnut blight, white-nose syndrome in bats), and hybridization. Their impacts are often irreversible once established at large scale.

Climate change interacts with all other threats, shifting species ranges poleward and upslope, altering the timing of seasonal events (phenological mismatch), increasing the frequency and intensity of extreme weather, and changing precipitation patterns in ways that affect habitat quality. Species with limited dispersal ability or specialized habitat requirements are particularly vulnerable. The fossil pollen record shows that past climate changes drove dramatic range shifts in tree species — spruce, for example, retreated northward after the Last Glacial Maximum — but those changes occurred over millennia; contemporary climate change is occurring over decades, potentially outpacing the ability of many species to track their shifting climate envelopes.

Pollution takes multiple forms in its impact on biodiversity: nutrient enrichment (eutrophication), toxic contaminants (pesticides, heavy metals), light pollution, noise pollution, and plastic waste. Biomagnification — the progressive increase in contaminant concentration up the food chain — means that top predators can accumulate toxin concentrations orders of magnitude higher than ambient levels, even when ambient concentrations seem negligible.

Conservation Approaches

Conservation biology is the applied science of protecting and restoring biodiversity. Its toolkit includes protected areas (parks, reserves, conservation areas), habitat restoration, management of invasive species, captive breeding and reintroduction for critically endangered species, and the application of population viability analysis to assess extinction risk and guide management.

Protected areas remain the cornerstone of conservation strategy, but their effectiveness depends on size, location, management, and connectivity. Isolated reserves function as ecological islands, subject to the same species-area relationship that governs natural islands: smaller reserves support fewer species and suffer higher extinction rates. Complementarity selection — designing reserve networks so that each new reserve adds maximally to the biodiversity already protected — is more efficient than simply protecting the largest or most charismatic areas.

Increasingly, conservation recognizes that protecting biodiversity is inseparable from sustaining ecosystem services — the benefits that functioning ecosystems provide to human well-being. These include provisioning services (food, water, timber, medicine), regulating services (climate regulation, flood control, water purification, pollination), supporting services (nutrient cycling, soil formation), and cultural services (recreation, aesthetic experience, spiritual values). The framing of biodiversity conservation in terms of ecosystem services has proved rhetorically powerful, though it also raises difficult questions about whose values are counted and what happens when ecosystem services and biodiversity protection conflict.

Key Terms

The following vocabulary was introduced in the course materials and readings for Weeks 1–2. Students should be able to define each term and explain its significance in an ecological context.

Scientific method and writing: hypothesis, null hypothesis, replication, statistical significance (p-value), peer review, abstract, keywords, introduction, methods, results, discussion, APA citation format.

Ecology foundations: ecology, biosphere, ecosystem, community, population, organism, anthropogenic biome, ecoliteracy.

Organism-level ecology: conditions, resources, response curve, fundamental niche, realized niche, ectotherm, endotherm, avoider, tolerator.

Biodiversity measurement: species richness, evenness, Shannon diversity index (H’), Simpson diversity index (D), Pielou’s J, alpha diversity, beta diversity, gamma diversity.

Classification: binomial nomenclature, taxonomy, Linnaean hierarchy, biological species concept, pre-zygotic isolation, post-zygotic isolation.

Biodiversity patterns and processes: latitudinal diversity gradient, species-area relationship, intermediate disturbance hypothesis, productivity hypothesis, eutrophication, niche complementarity.

Species and conservation: native species, exotic species, invasive species, naturalized garden, iNaturalist, citizen science, habitat loss, extinction vortex, overexploitation, biomagnification, protected area, ecosystem services.

Field methods: transect, quadrat, mark-recapture, basal area, DBH, density, succession (primary, secondary), climax community, edge effect, ecotone, watershed, riparian zone, lotic, lentic, benthic invertebrates, dissolved oxygen, eutrophication.

Wetlands: marsh, swamp, fen, bog, lagg, peat.