BY103 Environmental Science Midterm Review: Predators, Prey, and Biodiversity

Vocabulary practice flashcards covering keystone predators, competitive exclusion, trophic cascades, intertidal field studies, and the Yellowstone wolf reintroduction for the BY103 Environmental Science midterm review.

Keystone Predator

A top predator that keeps the dominant competitor in check, preventing it from monopolizing resources and thereby preserving the diversity of other species in the ecosystem.

Dominant Competitor

A species—such as mussels on a rocky shore or elk in Yellowstone—that expands to take over available space or food resources when freed from top-predator control.

Fast Loss

The rapid drop in community biodiversity (e.g., losing $2$ species per year in the reef simulation) that happens when a top predator is removed and the dominant competitor rapidly displaces other species.

Slow Recovery

The gradual pace at which biodiversity rebuilds (e.g., regaining only $1$ species per year in the reef model) following predator reintroduction, constrained by the need for space to be cleared and new species to arrive from nearby.

Robert Paine's Sea Star Experiment

A real-world intertidal study where removing the predatory sea star Pisaster caused rocky shore diversity to collapse from $17$ species to approximately $2$ species as mussels took over, while control areas maintained $16$ to $20$ species.

Pisaster

The genus of predatory sea star studied by Robert Paine on rocky shores that acts as a keystone predator by consuming mussels to open space for other marine organisms.

Sea Star Wasting Disease

A disease event in $2013$ that killed massive numbers of sunflower sea stars in Northern California, triggering an approximately $60\text{-fold}$ increase in purple urchins ($2014$ to $2015$) and the loss of over $90\%+$ of bull kelp across $217\text{ miles}$ of coastline.

Indirect Effect

An ecological relationship where one species influences another across multiple trophic levels without directly consuming it, such as sharks reducing sea lion populations, which in turn permits fish numbers to increase.

Control Group

A baseline comparison group in an experiment that is unmanipulated, such as Run $1$ (no sharks) in the food chain tray model or Paine's undisturbed rocky shore plots where sea stars remained.

Predator-Prey Lag

The cyclical delay between prey population changes and predator population responses; in Run $1$, prey (fish) peaked at Year $6$ with $8$ individuals, while predators (sea lions) peaked $2\text{ years}$ later at Year $8$ with $4$ individuals.

The Reef Show Setup

A $16\text{-square}$ model of a rocky shoreline initialized with $6$ mussels, $8$ different animal species, and $2$ empty squares, totaling $9$ kinds of organisms (with all mussels counted collectively as $1$ kind).

Fates Swap (Act 2)

The mid-simulation reversal between Year $5$ and Year $6$ where disease eliminated sea stars from Board A (causing species to drop from $13$ to $3$ by Year $10$) and sea stars returned to Board B (causing species to climb from $1$ to $6$ by Year $10$), with the lines crossing at Year $9$ at $5$ kinds each.

Simultaneous Updating Rule

The modeling rule requiring all population counts for a given year to be calculated solely from the prior year's numbers, preventing newly calculated values from influencing other species within the same turn.

Population Limits (Ocean Model)

The boundary constraints set in the food chain simulation preventing numbers from moving beyond fixed values: fish are restricted to $2$ through $12$, sea lions to $1$ through $5$, and sharks to $1$ through $4$.

Yellowstone Wolf Reintroduction

The release of $31$ wolves into Yellowstone in $1995$ and $1996$ ($\sim 70\text{ years}$ after extirpation), correlating with northern elk herd drops from $17{,}000$ to $3{,}915$ (by $2013$), young aspen browsing decreasing from $100\%$ to under $20\%$, and beaver colonies expanding from $1$ to $12$.

Confounding Factors (Yellowstone)

External variables present in the Yellowstone ecosystem—including human hunting, predation by bears and cougars, and drought—that complicate attributing vegetation and elk changes exclusively to wolves due to the lack of a wolf-free control area.

2024 Colorado State Study

A study reporting that willows in Yellowstone remained short in plots lacking fences or beaver dams, indicating that certain claims regarding full ecological recovery driven entirely by wolf restoration were exaggerated.