Table 1.
Scientific names, abbreviations, monoculture and mixture biomass productivity, R* indices of competitive ability (one-time measures of resource concentration in monoculture at peak biomass) and grazing impacts on biomass and seeds (the log difference between grazed and ungrazed plots) for the 11 focal species. All values are block averages; standard errors are in parentheses. R* values with different superscripted letters are significant from each other based on Tukey HSD tests (P < 0.05)
| Ungrazed biomass (g m−2) |
R* (resource concentrations in monocultures) |
Grazing impacts (ln(grazed) − ln(ungrazed)) |
||||||
|---|---|---|---|---|---|---|---|---|
| Species (abbreviation) | Mono | Mixture | DIN (μg g−1)* | P (μg g−1)† | H2O (%)‡ | Light (%)§ | Biomass (ln(g)) | Seed (ln(g)) |
| Native | ||||||||
| Amsinckia menziesii (Am) | 374.3 (±22.2) | 13.22 (±4.07) | 10.2 (±4.48)a,b | 18.07 (±3.84) | 12.0 (±1.17) | 46.2 (±4.46)a,b | −1.764 (±0.45) | −3.615 (±0.47) |
| Calandrinia ciliata (Cc) | 40.40 (±15.8) | 17.13 (±8.83) | 6.35 (±2.32)a,b | 13.59 (±2.65) | 11.6 (±0.77) | 87.6 (±6.17)d | −1.419 (±0.24) | −4.685 (±0.62) |
| Clarkia purpurea (Cp) | 486.9 (±41.6) | 99.24 (±15.5) | 3.07 (±0.94)a | 11.46 (±2.73) | 12.5 (±0.40) | 41.5 (±3.93)a | −3.269 (±0.10) | −5.654 (±0.90) |
| Vulpia microstachys (Vmi) | 292.7 (±33.9) | 35.07 (±10.0) | 6.92 (±1.84)a,b | 14.29 (±1.69) | 10.7 (±0.85) | 44.3 (±7.85)a,b | −2.105 (±0.54) | −5.029 (±0.47) |
| Vulpia octoflora (Vo) | 204.7 (±21.1) | 3.318 (±0.82) | 14.8 (±5.64)b | 19.81 (±2.01) | 11.6 (±1.11) | 74.2 (±6.56)c,d | −2.781 (±0.83) | −5.030 (±0.50) |
| Exotic | ||||||||
| Avena barbata (Ab) | 511.1 (±185.2) | 12.60 (±8.64) | 5.31 (±1.14)a,b | 11.25 (±1.53) | 11.2 (±0.71) | 60.8 (±7.18)a–c | −2.545 (±0.62) | −4.237 (±0.72) |
| Bromus hordeaceus (Bh) | 343.7 (±109.5) | 44.56 (±12.34) | 4.20 (±0.41)a,b | 12.54 (±2.08) | 11.7 (±0.53) | 46.3 (±1.82)a,b | −1.544 (±0.36) | −3.885 (±0.20) |
| Hordeum murinum (Hm) | 192.8 (±30.3) | 5.023 (±1.75) | 7.45 (±2.31)a,b | 12.55 (±2.00) | 12.4 (±1.00) | 80.4 (±3.37)c,d | −1.018 (±0.36) | −1.312 (±0.23) |
| Lamarckia aurea (La) | 315.0 (±26.3) | 6.315 (±2.65) | 3.77 (±0.56)a,b | 12.97 (±2.04) | 10.3 (±0.69) | 68.4 (±5.99)b–d | −2.087 (±0.25) | −3.319 (±0.16) |
| Polypogon monspeliensis (Pm) | 88.36 (±34.2) | 0.509 (±0.51) | 14.4 (±5.25)a,b | 14.31 (±3.26) | 11.3 (±1.16) | 85.8 (±2.28)c,d | −0.360 (±0.38) | −2.184 (±0.44) |
| Vulpia myuros (Vmy) | 275.6 (±60.8) | 61.92 (±20.3) | 3.50 (±0.48)a,b | 13.66 (±1.33) | 9.9 (±0.31) | 63.4 (±7.39)a–d | −1.726 (±0.24) | −3.677 (±0.45) |
R* values for nitrogen, i.e. dissolved inorganic nitrogen (DIN), are based on the sum of nitrate and ammonium concentrations. Species differ significantly in R* measurements of nitrate (F = 2.48, d.f. = 10, P = 0.02) and DIN (F = 2.059, d.f. = 10, P = 0.05).
Species do not differ significantly in R* measurements of P (F = 1.60, d.f. = 10, P = 0.14).
Species do not differ significantly in R* measurements of soil moisture (F = 1.87, d.f. = 10, P = 0.08).
R* for light is calculated by dividing PAR at the soil surface by PAR immediately above the plant canopy, and multiplying this number by 100 (the per cent of light that reaches the soil surface in monoculture); we assume that the lower this value, the more competitive the species is for light. Species differ significantly in R* measurements of light (F = 9.88, d.f. = 10, P < 0.001).