Conservation Biology - Exam Review

Easter Island

A cautionary ecological case study of human overexploitation. Deforestation of native palms and overhunting led to ecological collapse, loss of ecosystem services, and societal decline, demonstrating that finite island ecosystems have strict carrying capacities.

Channel Islands

An archipelago off southern California that serves as a classic system illustrating apparent competition, trophic cascades, and the complex impacts of invasive species.

Island Foxes, Feral Pigs, and Golden Eagles

• Invasive feral pigs provided an abundant food source that attracted mainland golden eagles to colonize the Channel Islands.

• The diurnal native island foxes became incidental secondary prey; hyperpredation by golden eagles drove fox populations toward near-extinction.

• Native bald eagles (which ate primarily fish/carrion and maintained territories against golden eagles) had previously been extirpated by DDT, leaving an open niche.

Conservation Biology

A mission-driven, multidisciplinary crisis discipline dedicated to evaluating human impacts on biodiversity and developing practical strategies to prevent species extinctions and maintain healthy ecological processes.

Marion Island

A sub-Antarctic island where introduced house mice decimated native invertebrate populations and began attacking breeding albatross chicks, demonstrating how single invasive introductions can trigger massive disruption in naive ecosystems.

Biodiversity

The total variety of life across all structural and functional levels of biological organization, typically measured across genes, species, and ecosystems.

Three Elements of Biodiversity

• Genetic Diversity: Heritable variation within and between populations of a species.

• Species (Organismal) Diversity: The variety and abundance of different species inhabiting an area.

• Ecosystem/Ecological Diversity: The variety of distinct habitats, biological communities, and ecological processes across landscapes.

Species Concepts

• Biological Species Concept (BSC): A group of individuals that can breed among themselves in the wild and do not breed with individuals of another group

• Morphological (Typological) Species Concept: A group of individuals that is morphologically, physiologically, or biochemically distinct from other groups in some important characteristic

• Phylogenetic (Evolutionary) Species Concept: A group of individuals that share unique similarites of their DNA and hence their evolutionary past

Cryptic Diversity

The existence of distinct, reproductively isolated species that appear virtually identical in morphology and can only be resolved using genetic tools.

Hybridization

Interbreeding between individuals of genetically distinct populations or species, which can result in hybrid zones, speciation, or the genetic swamping and extinction of rare taxa.

Speciation

The evolutionary process by which populations diverge to form distinct, reproductively isolated species (e.g., allopatric speciation via geographic barriers, sympatric speciation within a shared range).

Richness (S)

The raw count of distinct species present in a defined community.

Diversity

A composite metric incorporating both species richness and their relative abundances (evenness; e.g., Shannon-Wiener or Simpson indices).

Rivet Hypothesis

Proposed by Paul and Anne Ehrlich; analogizes species in an ecosystem to rivets in an airplane wing. Losing a few rivets may cause minimal functional change, but as species loss continues, a critical threshold is crossed, precipitating abrupt ecological collapse.

Keystone Species

A species whose ecological impact on community structure and function is disproportionately large relative to its low biomass or abundance (e.g., sea otters regulating sea urchin populations to preserve kelp forests).

Dominant Species

A species with a large ecological impact simply due to high total biomass or abundance (e.g., reef-building corals, dominant forest canopy trees).

Mutualisms

Interspecific interactions where both participating species derive a net fitness benefit (e.g., plants and their specialized pollinators, mycorrhizal fungi and plant root systems).

Ecosystem Engineer

An organism that directly modulates the availability of resources for other species by physically creating, modifying, maintaining, or destroying habitats:

Umbrella Species

A species with extensive home-range or habitat requirements such that protecting its natural habitat automatically secures protection for numerous co-occurring species.

Species-Area Relationship, S=cAz

Describes how species richness (S) scales with habitat area (A), where c is a taxon-specific scaling constant and z reflects the slope on a log-log plot (typically 0.20 to 0.35 for terrestrial habitat patches and islands).

Sampling Artifact / Passive Sampling

Larger areas sample more individual organisms, inherently capturing more species by chance.

Habitat Heterogeneity

• Larger physical areas encompass a broader variety of microhabitats, soil types, elevations, and niches.

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Colonization-Extinction Dynamics (Island Biogeography)

Larger areas support larger population sizes (reducing stochastic extinction rates) and provide larger target areas for dispersing immigrants.

Speciation-Extinction Equilibrium

On macro-geographic scales, larger regions allow broader distributions, increasing opportunities for vicariance and allopatric speciation while lowering extinction risk.

Latitudinal Gradient in Species Richness (LDG)

The global pattern where biological diversity peaks in the tropics and steadily declines toward the poles across most taxonomic groups.

Four Groups of Mechanisms to Explain LDG

• Null models (geometric constraints on species ranges),  

Null Model: a pattern–generating model based on randomization of ecological data. The randomization produces a pattern that would be expected in the absence of a particular mechanism 

• Ecological hypotheses (productivity and carrying capacity) 

• Species – energy hypothesis – Tropics more productive; more productivity more individuals/area; more individuals contain more species 

• Historical hypotheses (geologic time and area available for diversification),  

• Time-and-area hypothesis – tropical environments are older and bigger 

•  Evolutionary hypotheses (differences in speciation and extinction rates). 

Tropics as a “cradle” for the generation of new taxa or a “museum” for the preservation of existing diversity 

Elevational Gradient in Species Richness

Patterns of species turnover along mountain slopes, typically displaying either a monotonic decline with increasing altitude or a mid-elevation hump (peaking at intermediate elevations where ecotones overlap and temperature/moisture balance is optimal).

Indicator Species

A species whose presence, absence, population size, or physiological status reflects the health, ecological integrity, or environmental contamination of a given ecosystem.

Intermediate Disturbance Hypothesis (IDH)

Predicts that local species diversity peaks at intermediate frequencies or intensities of ecological disturbance. High disturbance eliminates disturbance-intolerant species, whereas low disturbance permits dominant competitors to competitively exclude weaker species.

Discovering Species

The ongoing process of surveying, describing, and cataloging undescribed taxa using museum collections, morphological taxonomy, environmental DNA (eDNA), and genomic barcoding.

Ecosystem Function

The primary biological and geochemical processes that operate within an ecosystem, including biomass production, nutrient cycling, water filtration, and carbon sequestration.

Shape of Bio-Eco Func Relationships

• Most BEF curves show a saturating (asymptotic) response: adding species increases ecosystem function rapidly at low diversity levels, but the rate of functional gain plateaus at higher richness because of functional redundancy among species.

Cedar Creek Experiment

David Tilman's long-term grassland plots in Minnesota manipulating plant species richness. The experiment demonstrated that plots with higher plant diversity exhibited higher primary productivity and showed greater drought resistance and resilience over time.

Diversity-Productivity

The principle that communities containing higher plant species richness produce higher aggregate aboveground biomass, primarily driven by complementary resource use.

Niche Differentiation (Complementarity)

Species use limited resources (nutrients, rooting depths, light spectra) in functionally different ways or facilitate one another, maximizing resource capture.

Sampling (Selection) Effect

Species-rich communities have a mathematically higher probability of including a disproportionately productive or high-performing species by chance.

Diversity-Stability

Species-rich communities exhibit lower aggregate temporal variability in total biomass in response to environmental disturbances.

Portfolio Effect

When species respond asynchronously to change, the ecosystem stability increases

Diversity-Invasion

The hypothesis (first popularized by Charles Elton) that species-rich native communities are more resistant to colonization by non-native species because available niches and limiting resources are more fully occupied.

Diversity-Invasion Paradox:

• At small local scales (experimental plots), diversity negatively correlates with invasion success due to competition and resource depletion.

• At broad spatial scales (landscapes/regions), native diversity positively correlates with invasive richness because favorable abiotic conditions (high resources, mild climate) support high numbers of both native and non-native species.

Diversity-Diversity

The trophic pattern where plant diversity directly promotes the diversity of higher trophic levels (herbivores, parasitoids, predators, pollinators, and soil mutualists).

Ecological Economics

• A subfield that models the human economy as a wholly dependent subsystem embedded within the finite global biosphere, emphasizing physical limits to growth, non-market values, and intergenerational sustainability.

Tragedy of the Commons

Proposed by Garrett Hardin; the depletion or degradation of an open-access, unmanaged shared resource because individual actors act rationally in self-interest to maximize immediate personal harvest.

Externalities

hidden costs to economic exchanges

Cost-Benefit Analysis (CBA)

compares the values gained against the costs of the project or resources use

Barriers to Ecological Economics

• Difficulties in calculating costs

• Perverse subsidies

• Discount rates - assigning a lower current value to resources used in the future on the grounds that it is better for society to hsve money now and invest it for greater wealth

Ecosystem Services

• The direct and indirect benefits that healthy natural ecosystems provide to human societies, categorized by the Millennium Ecosystem Assessment into provisioning (food, timber, clean water), regulating (climate, flood control), supporting (nutrient cycling, soil formation), and cultural (recreation, spiritual value).

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Existence Value

The non-use value people derive solely from knowing that a species, wilderness area, or ecosystem continues to exist, independent of any current or future use.

Direct Use Value

Tangible value derived from the direct harvesting, consumption, or non-consumptive physical use of biological resources (e.g., harvesting timber, commercial fishing, ecotourism).

Indirect Use Value

Functional benefits derived from ecosystem processes that support human wellbeing without direct physical consumption (e.g., wetlands purifying drinking water, forests stabilizing slopes against landslides).

Option Value

The economic value of preserving a species, gene pool, or natural habitat for potential future discovery and use (e.g., bioprospecting wild plants for life-saving pharmaceuticals).

Environmental Ethics

The branch of philosophy that evaluates the moral relationship between human beings and the natural world, determining whether moral consideration extends beyond humans to animals, plants, and ecosystems.

Ethics and the Endangered Species Act (ESA)

The ESA embodies an ecocentric and deontological ethic: it legally codifies that imperiled species possess an intrinsic right to exist that takes precedence over short-term economic gains, making species preservation a federal imperative regardless of direct utility.

Three Views on Species Rights:

• Anthropocentric: Moral standing belongs exclusively to humans; species and natural environments only hold value to the extent that they serve human utility and interests.

• Biocentric (Individualistic): Moral standing extends to all individual living organisms capable of suffering or possessing a "will to live" (sentience/individual life-centered).

• Ecocentric (Holistic): Moral standing resides primarily in ecological wholes—populations, communities, species, and functional ecosystems—emphasizing stability, integrity, and beauty (as articulated in Aldo Leopold's Land Ethic).

Ethical Arguments for Preserving Biodiversity

• Intrinsic Value: Species have inherent worth and a right to exist independent of human valuation.

• Intergenerational Justice: Present generations bear a moral obligation to leave a functioning, biodiverse planet for future human generations.

• Biophilia: Humans share an evolutionary affinity for life; safeguarding biodiversity supports human psychological and spiritual well-being.

Enlightened Self-Interest

An anthropocentric viewpoint recognizing that safeguarding biodiversity and ecological processes is ultimately essential for our own species' long-term survival, economic prosperity, and health.

Trophy Hunting Costs and Benefits

• Benefits:

  • Generates substantial revenue for anti-poaching enforcement, game guards, and habitat monitoring.

  • Incentivizes private landowners and rural communities to preserve vast tracts of wilderness rather than converting wildland to livestock grazing or agriculture.

  • Provides local employment and meat distribution to indigenous communities.

• Costs:

  • Targeted selective harvest of dominant males with large horns/manes can disrupt social dynamics, alter evolutionary traits, and cause pride takeovers with subsequent infanticide (e.g., in lions).

  • Corruption, mismanagement, and poorly monitored hunting quotas can depress target wildlife populations.

Trophy Hunting Ethical Arguments For and Against:

• For (Utilitarian / Pragmatic): Hunting a limited number of individual animals generates revenue and territorial protection that conserves viable populations, intact habitats, and broader biodiversity across the landscape.

• Against (Deontological / Animal Rights): Killing sentient, highly intelligent wild animals for recreational sport or trophies is fundamentally unethical, regardless of economic outcomes.