In AP Biology, species richness is the number of different species present in a community. It's one piece of biodiversity, and higher richness generally makes an ecosystem more resilient to environmental change (Topic 8.6).
Species richness is simply a head count of the different species living in a community. If a prairie has 40 plant species and a nearby plot has 12, the first plot has greater species richness. That's it, just the number of distinct species, not how many individuals of each.
In the CED, this idea shows up under biodiversity (Topic 8.6). The big takeaway is the connection to resilience. Ecosystems with more component parts and more diversity among those parts tend to bounce back from disturbances better than simple, low-diversity ones (EK 8.6.A.1). Think of richness like a backup system: when many species are doing similar jobs, losing one doesn't break the whole machine.
Species richness lives in Unit 8: Ecology, Topic 8.6 Biodiversity. It's the concrete metric behind learning objective AP Bio 8.6.A, which asks you to describe how ecosystem diversity relates to resilience. Per EK 8.6.A.1, low-diversity systems (natural or artificial, like a monoculture cornfield) are often less able to handle environmental change. The flip side connects to AP Bio 8.6.B and keystone species, where pulling one critical species out can collapse an ecosystem regardless of how many other species are present. So richness isn't just trivia, it's the variable you reason with when you predict how a community responds to disturbance.
Keep studying AP® Biology Unit 8
Species Diversity (Unit 8)
Species richness is one ingredient in species diversity. Diversity counts the number of species AND how evenly individuals are spread among them, so richness is the 'how many kinds' half of the full diversity picture.
Keystone Species (Unit 8)
Richness tells you how many species are present, but a keystone species reminds you that not all species count equally. Remove a keystone and the ecosystem can collapse even when overall richness looked high (EK 8.6.B.1).
Genetic Diversity (Unit 7-8)
Richness is diversity between species; genetic diversity is variation within a single species. Both buffer against change, and both connect back to natural selection from Unit 7, where variation is the raw material that lets populations adapt.
Producers (Unit 8)
Producers form the base of every food web, so the richness of producer species often sets the ceiling for diversity at higher trophic levels. More plant species can support more consumers (EK 8.6.A.2).
Expect species richness in Unit 8 multiple-choice stems built around data: a study finds plots with higher plant species richness show more stable ecosystem functions over time, and you pick the concept it supports (the answer ties richness to resilience). You'll also see experimental-design questions, like choosing the best setup to test how prairie biodiversity affects recovery from extreme weather, where the right design manipulates richness and measures stability. On FRQs, you'd use richness to justify a prediction: explain why a more diverse community recovers faster from disturbance, or why removing a species (especially a keystone) shifts long-term structure. The skill is reasoning from richness to a resilience outcome, not just defining the word.
Species richness is only the count of different species. Species diversity goes further by also factoring in evenness, meaning how the individuals are distributed among those species. A community with 10 species where one species dominates has the same richness but lower diversity than one with 10 evenly balanced species.
Species richness is just the number of different species in a community, nothing about abundance or evenness.
Higher species richness generally makes ecosystems more resilient to environmental change, while low-diversity systems are often more fragile (EK 8.6.A.1).
Richness is one component of species diversity, which also includes how evenly individuals are spread across species.
A high richness count can still hide vulnerability if a keystone species is present, because losing that one species can collapse the system (EK 8.6.B.1).
On the exam, use richness to predict resilience and stability, not just to define a vocabulary word.
Producer richness often sets the foundation for diversity higher up the food web (EK 8.6.A.2).
It's the number of different species present in a community. In the CED (Topic 8.6) it's used to reason about how diverse ecosystems tend to be more resilient to environmental change.
No. Richness is just the count of species, while diversity also accounts for evenness, meaning how individuals are distributed among those species. Two communities can have identical richness but different diversity if one is dominated by a single species.
Usually, but not guaranteed. Greater richness generally increases resilience (EK 8.6.A.1), yet losing a single keystone species can still collapse an ecosystem regardless of how rich it is (EK 8.6.B.1).
When many species fill overlapping roles, the loss of one doesn't break the whole system, so richer communities recover from disturbances like droughts or storms more reliably than low-diversity ones.
It shows up in Unit 8 data-analysis and experimental-design questions, often asking you to connect higher richness to greater stability or resilience, or to design a study testing that relationship in something like a prairie ecosystem.
Connect this key term to the AP exam workflow: review the course, practice questions, and check related study tools.
Review units, study guides, and course resources.
Check this vocabulary in multiple-choice context.
Apply key concepts in written AP responses.
Estimate the exam score you are working toward.
Review the highest-yield facts before practice.
Put the full course together before test day.