Species-Area Relationship Calculators

0 calculators tagged with “Species-Area Relationship”

The species-area relationship (SAR) describes the empirical observation that larger habitat areas support more species. The relationship follows a power law: S = c × A^z, where S is species richness, A is area, c is a constant related to the study region, and z is the slope (typically 0.20–0.35 in island systems, 0.12–0.20 for nested samples within continuous habitats). The SAR is the empirical foundation of island biogeography theory (MacArthur and Wilson 1967) and has profound implications for conservation — habitat fragmentation reduces effective area, predicting species loss.

All Calculators

No calculators found for this topic.

SAR Formula

S = c × A^z

Linearized form: log(S) = log(c) + z × log(A). z = slope of log(S) vs. log(A) regression; c = intercept (species richness at A = 1). Example: z = 0.25 means doubling area increases species richness by ~19% (2^0.25 − 1).

z Values

  • True oceanic islands: z ≈ 0.30–0.40 (high isolation increases turnover)
  • Continental habitat islands (forest fragments): z ≈ 0.20–0.30
  • Nested samples within continuous habitats: z ≈ 0.10–0.20
  • Global scale: z ≈ 0.25 for most taxonomic groups

Island Biogeography Theory

MacArthur and Wilson (1967) proposed that island species richness is determined by the balance between immigration (decreasing as richness increases) and extinction (increasing as richness increases). Equilibrium species number = intersection of immigration and extinction curves. Larger islands: lower extinction rates → more species. Closer islands: higher immigration → more species. Empirically tested and confirmed by Simberloff and Wilson's mangrove island defaunation experiments.

Conservation Implications

Habitat loss predicts proportional species loss: if z = 0.25, a 90% reduction in area predicts loss of ~44% of species (1 − (0.1)^0.25). This framework guides minimum habitat patch size requirements and corridor design in landscape conservation planning.

Glossary

Species-Area Relationship (SAR)
S = c × A^z; the power-law relationship between habitat area and species richness; z ≈ 0.25 for islands; predicts species loss from habitat reduction.
z-Value (SAR)
The slope of log(S) vs. log(A); typically 0.20–0.35 for island systems and 0.10–0.20 for nested continental samples; determines sensitivity of species richness to area loss.
Island Biogeography Theory
MacArthur and Wilson (1967) model predicting island species richness as equilibrium between immigration and extinction rates; larger and closer islands have more species.

Frequently Asked Questions

The species-area relationship (SAR) is the empirical pattern that larger areas contain more species, following the power law S = c × A^z. On a log-log plot, this is linear: log(S) = log(c) + z × log(A). z is typically 0.25 for island systems and 0.15 for nested continental samples. SAR applies across taxa (plants, birds, insects) and spatial scales. It underpins island biogeography theory and is used to predict species loss from habitat destruction.

z is the slope of the log(S) vs. log(A) regression — the rate at which species richness increases with area. z = 0.25 means that for every 10-fold increase in area, species richness roughly doubles (10^0.25 = 1.78). Higher z (0.35–0.40) is typical of true oceanic islands with high isolation and turnover; lower z (0.10–0.20) characterizes nested samples within continuous habitats where all species have equal access to all areas. The value of z determines how severely species loss is predicted to follow habitat loss.

MacArthur and Wilson's (1967) theory predicts that island species richness reaches an equilibrium between immigration (new species arriving) and extinction (resident species going locally extinct). Two predictions: (1) Larger islands have higher equilibrium richness — lower per-species extinction rates (more resources, larger populations). (2) Islands closer to the mainland have higher richness — higher immigration rates replenishing extinctions. The theory was empirically confirmed by Simberloff and Wilson's defaunation and recolonization experiments on small mangrove islands in the Florida Keys.

Habitat fragmentation reduces the effective area of habitat patches, predicting species loss via the SAR: if z = 0.25 and habitat is reduced by 90% (remaining 10%), predicted remaining species = (0.10)^0.25 = 0.56 = 56% of original species (44% loss). Fragmentation also creates edge effects, increases isolation, and reduces immigration to compensate for extinctions — potentially steepening effective z above the landscape-level value. Conservation applications: minimum viable reserve size, SLOSS debate (Single Large Or Several Small reserves), and wildlife corridors to maintain immigration and reduce isolation effects.