Extended Formula Derivation

The two core diet composition metrics share the same numerator (n_i) but differ in their denominator. Frequency of occurrence (%FO) uses the total number of scat samples (N) as the denominator, treating each scat as a Bernoulli trial that either contains or does not contain prey item i. Percent occurrence (%PO) uses the sum of all prey hits across all items (∑n_j), so each prey item's share is normalised to total prey occurrences rather than to total scats.

Because a single scat can contain multiple prey items, the sum of %FO across all prey items often exceeds 100%, while the sum of %PO is always exactly 100%. This is why both metrics should be reported together — %FO answers "how many scats contained this prey?" while %PO answers "what fraction of the diet does this prey item make up?"

Assumptions

• Scats are correctly identified to the predator species (use genetic confirmation when sympatric carnivores overlap).
• Prey remains are correctly identified from hair, bone, feather, scale, or seed fragments.
• Differential digestion among prey is not corrected for in raw %FO and %PO — small/soft prey may be under-detected.
• Sampling effort is sufficient to reach the asymptote of a cumulative prey-item curve (typically ≥ 50–100 scats).
• Each scat is treated as an independent observation; collect across spatial and temporal replicates to avoid pseudo-replication.

Limitations

• %FO and %PO do not estimate biomass consumed — large prey items contribute disproportionately to nutrition but may appear in fewer scats.
• Highly digestible prey (e.g., small mammals consumed whole) may be over-represented relative to large prey.
• Hair-only identification cannot distinguish scavenging from predation.
• Insect remains may be over-represented because of their indigestible chitinous exoskeletons.
• For biomass-corrected estimates, apply correction factors from Floyd, Mech & Jordan (1978) or Ackerman, Lindzey & Hemker (1984).

Use this calculator when:

• ✓ You have collected scats from a known predator species and identified prey remains in each sample.
• ✓ You want to summarise diet composition as %FO and %PO for a manuscript, thesis, or report.
• ✓ You want to compare diet between seasons, sites, or sex/age classes within a species.
• ✓ Your sampling effort is at or near the cumulative prey-item asymptote (typically ≥ 50 scats).

Do NOT use this calculator when:

• ✗ Sample sizes are very small (< 30 scats) — confidence intervals become uninformative.
• ✗ You need biomass estimates — apply published correction factors first.
• ✗ You want to test diet selectivity — combine with prey-availability data and use Manly's α or Ivlev's E.
• ✗ Predator species identification is uncertain — confirm scat origin with genetic methods.

Real-world USA examples:

1. Coyote diet in Yellowstone (Wyoming) — quantifying ungulate vs small-mammal contributions across summer and winter.
2. Bobcat scat analysis in Texas Hill Country — assessing the role of cottontail and small rodents during drought years.
3. Gray wolf diet on Isle Royale (Michigan) — long-term moose dependency and beaver subsidy.
4. Mountain lion scat in Idaho — evaluating mule deer reliance versus elk during winter.

Sampling design guidance:

• Collect 50–100 scats per season per site.
• Plot a cumulative prey-item curve to confirm sample size adequacy.
• Stratify by season and habitat type to capture diet shifts.
• Store scats frozen or in alcohol; process under sterile conditions.

1. Enter your data — Paste scat counts (e.g., 52, 48, 55, 61, 47) into the textarea, or use Column Entry for labelled prey items, or upload a CSV/Excel file.
2. Choose a sample dataset — Five USA carnivore datasets are pre-loaded for testing.
3. Set the study area — Optional but recommended; populates reporting templates and the PDF cover.
4. Edit the group name — Default is "Coyote (Canis latrans)"; change to your study species.
5. Enter total scats (N) — Required for %FO calculation; defaults to the dataset's reported N.
6. Configure thresholds — Choose diet-diversity threshold and minor-prey cutoff.
7. Click "Run Scat Diet Analysis" — Computes %FO and %PO for every prey item, with diet tier classification.
8. Read the four colourful charts — %FO bar, %PO donut, cumulative contribution, and diet profile scatter.
9. Read the diet composition table — Each row shows raw count, %FO, %PO, and diet tier (primary/secondary/incidental).
10. Read the detailed interpretation and conclusion — Plain-language paragraphs with study area substitution.
11. Copy a reporting example — Five styles (ecology journal, thesis, plain-language, conference abstract, monitoring) plus a research poster panel.
12. Export — Download Doc (.txt) or PDF for archiving.