The green outline is a sampling quadrat โ a fixed-size frame ecologists lay over a habitat to count individuals without surveying the whole site. Every plant marker in the field belongs to one of the species-pool colours; only markers inside the quadrat (bright, upright) count toward the indices below โ everything outside (dim, low) is the part of the community the survey never sees. Species are drawn from a rank-abundance model, so the pool is realistically uneven: a few species are common, most are rare.
S = distinct species counted inside the quadrat
p_i = n_i / N (relative abundance of species i)
H' = โ ฮฃ p_i ยท ln(p_i) (Shannon diversity)
J = H' / ln(S) (Pielou's evenness, 0-1)
- Quadrat size โ a bigger frame samples more individuals and usually finds more species, the same species-area effect that makes real biodiversity surveys sensitive to plot size.
- Species pool โ how many species exist in the wider community the quadrat is dropped into; a richer pool raises the ceiling on S and H'.
- Abundance dominance โ how lopsided the underlying abundances are. Low dominance keeps species roughly equally common (J near 1); high dominance lets one or two species take over, so a small quadrat may sample only the dominant species even from a rich pool.
- Resample plot โ draws a brand-new random community with the current settings, showing how much a single quadrat placement can vary by chance alone.
Real-world relevance: exactly this trade-off โ quadrat size vs. survey effort vs. estimated diversity โ governs how conservation biologists design field inventories, and why H' and J (not raw species counts) are used to compare sites surveyed at different scales.