When Resources Run Short
Aligned to MS-LS2-1 — Next Generation Science Standards.
What this lesson teaches
Organisms compete for resources like food, water, sunlight, and space. When a resource becomes scarce, populations that depend on it usually shrink, and when it is plentiful, those populations often grow — the data reveal these patterns.
Worked examples
Example 1
During a drought, a pond shrinks and its plants die back; the data show fish and frog numbers falling as their food and oxygen decline, then rising again after the rains return and resources recover.
Example 2
Introduce a competitor and the same thing happens without any drought: two species needing the same food cannot both stay at full numbers.
Example 3
Populations rarely sit still. Predator and prey numbers usually cycle, with the predator peak lagging the prey peak.
Practice questions
- Track how many birds visit a feeder that is full versus nearly empty over several days.
- Graph a set of population numbers against rainfall data and describe the pattern you see.
- Explain, using evidence from your graph, how a change in one resource affected the size of a population.
Watch the lesson
Every lesson comes with a video taught in English and Spanish — the same video the QR code in the printed workbook opens.
▶ Watch this lessonEn español
Cuando los recursos escasean
Los organismos compiten por recursos como comida, agua, luz solar y espacio. Cuando un recurso se vuelve escaso, las poblaciones que dependen de él suelen reducirse, y cuando es abundante, esas poblaciones a menudo crecen — los datos revelan estos patrones.
Ejemplo 1: Durante una sequía, un estanque se encoge y sus plantas mueren; los datos muestran que el número de peces y ranas baja al disminuir su alimento y oxígeno, y luego sube de nuevo cuando regresan las lluvias y se recuperan los recursos.
Ejemplo 2: Introduce un competidor y pasa lo mismo sin ninguna sequía: dos especies que necesitan el mismo alimento no pueden mantenerse las dos en números plenos.
Ejemplo 3: Las poblaciones rara vez se quedan quietas. Los números de depredador y presa normalmente oscilan, con el pico del depredador retrasado respecto al de la presa.
More Ecosystems: Interactions, Energy & Dynamics lessons
Teach this lesson today
An AI tutor that guides with questions instead of just giving answers — all K–12 core subjects, every child in the family.
Start free — no card required