Table 1. Hypotheses, predictions, and covariates used to estimate factors influencing elk abundance and recruitment.
| Hypothesis | Prediction | Covariates |
|---|---|---|
| 1) Winter severity: | ||
| a) Temperature | As winter temperatures decrease, abundance and recruitment decrease | Mean winter temperature, mean monthly minimum winter temperature (November–March) |
| b) Snow | As snow depth or total snowfall increases, abundance and recruitment decrease | Mean snow depth, total snowfall (November–March) |
| 2) Spring bottleneck: | ||
| a) Spring quality | As spring temperature and/or precipitation increases, abundance and recruitment increase | Mean spring temperature, total spring precipitation (April–May) |
| b) Spring timing | As the last spring freeze is later, abundance and recruitment decrease | Last spring freeze |
| c)Winter duration | As winter duration increases, abundance and recruitment decrease | Winter duration (# days between first fall freeze and final spring freeze) |
| 3) Maternal carry-over: | ||
| a) Summer quality | As growing degree days, summer temperatures and/or summer precipitation increase, abundance and recruitment increase in the following year | Mean summer temperature, total summer precipitation, growing degree days (June–August; t-1) |
| b) Summer Productivity | As SPEI decreases, abundance and recruitment increase in the following year | 6-month SPEI calculated in July (forest SPEI), 3-month SPEI calculated in September (grassland SPEI) (t-1) |
| c) Fall quality | As fall temperatures and/or precipitation increase, abundance and recruitment increase in the following year | Mean fall temperature, total fall precipitation (September–October; t-1) |
| d) Fall timing | As the first fall freeze is later, abundance and recruitment increase in the following year | First fall freeze (t-1) |
| 4) Predation: | ||
| As abundance of brown bears increases, recruitment decreases | Reconstructed brown bear abundance | |
| 5) Timber Harvest: | ||
| a) Timber harvest increases habitat suitability | As area of timber harvest or young timber stands increases, recruitment increases | Square kilometers of timber stands age <1, 1–5, 6–30, and >30 years since harvest, square kilometers of all harvested area |
| b) Timber harvest decreases habitat suitability | As area of timber harvest or young timber stands increases, recruitment decreases | Square kilometers of timber stands age <1, 1–5, 6–30, and <30 years since harvest, square kilometers of all harvested area |
Hypotheses and predictions were tested on elk early calf recruitment (calves per 100 adult females in July–August) and population counts of elk on Afognak and Raspberry islands, Alaska, USA. Predictors for the year prior to the composition and population counts are represented as t-1. SPEI is the standardized precipitation evapotranspiration index (see methods for details).