Table 5.
Mixed model effects of white-tailed deer a) access/exclusion and b) population density on introduced, native and total plant species richness based on floristic composition data collected from deer-access (unfenced) and deer-exclusion (fenced) plots at 23 sites in east-central and north-eastern USAa. Proportion introduced plant species richness was evaluated based on the interaction of the deer effect with total species richness; a significant interaction indicates that the ratio of introduced to total plant species richness (i.e. proportion introduced) varies with the deer effect. For random effect results, see Supporting Information—Table S3. P values and LSmeans treatment test results are in bold print if significant at the alpha level α < 0.05.
| Introduced species richness | Native species richness | Total species richness | |
|---|---|---|---|
| a) Deer access/exclusion | |||
| Intercept (SE) | 0.4 (0.2) | 3.2 (0.2) | 4.0 (0.3) |
| DA/DE coefficient (SE) | –0.04 (0.07) | 0.39 (0.06) | 0.32 (0.06) |
| F statistic (DFn,DFd) | 0.31 (1,220) | 46 (1,222) | 25 (1,222) |
| P value | 0.6 | <0.001 | <0.001 |
| LSmeans treatment test | – | DE > DA | DE > DA |
| DA estimate (LCI–UCI) | – | 3.2 (2.7–3.8) | 4.0 (3.4–4.5) |
| DE estimate (LCI–UCI) | – | 3.6 (3.1–4.1) | 4.3 (3.7–4.8) |
| Total species richness coefficient (SE) | 0.044 (0.004) | – | – |
| F statistic (DFn,DFd) | 160 (1,397) | – | – |
| P value | <0.001 | – | – |
| DA/DE * Total species richness coefficient (SE) | 2 × 10−4 (0.003) | – | – |
| F statistic (DFn,DFd) | 0.004 (1,219) | – | – |
| P value | 0.9 | – | – |
| n | 404 | 446 | 446 |
| # Sites | 18 | 23 | 23 |
| b) Deer density | |||
| Intercept (SE) | 0.2 (0.4) | 3.9 (0.4) | 4.5 (0.5) |
| DD coefficient (SE) | 0.005 (0.007) | –0.020 (0.009) | –0.01 (0.01) |
| F statistic (DFn,DFd) | 0.64 (1,22) | 5.1 (1,19) | 2.1 (1,19) |
| P value | 0.4 | 0.04 | 0.2 |
| Total species richness coefficient (SE) | 0.031 (0.008) | – | – |
| F statistic (DFn,DFd) | 15 (1,183) | – | – |
| P value | <0.001 | – | – |
| DD * Total species richness coefficient (SE) | 3 × 10−4 (1 × 10−4) | – | – |
| F statistic (DFn,DFd) | 3.9 (1,185) | – | – |
| P value | 0.049 | – | – |
| n | 190 | 211 | 211 |
| # Sites | 17 | 22 | 22 |
aSquare-root transformations of species richness were used to meet the assumption of homogeneity of residuals. SE = standard error; DA = deer access; DE = deer exclusion; DFn = degrees of freedom, numerator; DFd = degrees of freedom, denominator; LCI = lower confidence interval; UCI = upper confidence interval; n = number of observations; DD = deer density.