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We lack a strong understanding of how organisms with complex life histories respond to climate variation. Many stream-associated species have multi-stage life histories that are likely to influence the demographic consequences of floods and droughts. However, tracking stage specific demographic responses requires high-resolution, long-term data that are rare. We used eight years of capture-recapture data for the headwater stream salamander Gyrinophilus porphyriticus to quantify the effects of flooding and drying magnitude on stage-specific vital rates and population growth. Drying reduced larval recruitment but increased the probability of metamorphosis (i.e., adult recruitment). Flooding reduced adult recruitment but had no effect on larval recruitment. Larval and adult survival declined with flooding but were unaffected by drying. Annual population growth rates (lambda, ) declined with flooding and drying. Lambda also declined over the study period (2012 – 2021), although mean was 1.0 over this period. Our results indicate that G. porphyriticus populations are resilient to hydrologic variation due to compensatory effects on recruitment of larvae vs. adults (i.e., reproduction vs. metamorphosis). Complex life cycles may enable this resilience to climate variation by creating opportunities for compensatory demographic responses across stages. However, more frequent and intense hydrologic variation in the latter half of this study contributed to a decline in over time, suggesting that increasing environmental variability poses a threat even when demographic compensation occurs.
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The Demographic Basis of Population Growth: A 32‐Year Transient Life Table Response Experiment
ABSTRACT It has recently been recognised that populations are rarely in demographic equilibrium, but rather in a ‘transient’ state. To examine how transient dynamics influence our empirical understanding of the links between changes in demographic rates and population growth, we conducted a 32‐year study of Columbian ground squirrels. The population increased rapidly for 10 years, followed by a 2‐year crash, and a gradual 19‐year recovery. Transient life table response experiment (LTRE) analysis showed that demographic stochasticity accounted for approximately one‐fourth of the variation in population growth, leaving the majority to be explained by environmental influences. These relatively small rodents appeared to have a slow pace of life. But unlike the general pattern for large mammals with slow life histories, ground squirrel survival did not exhibit low variation associated with environmental ‘buffering’; instead, survival varied substantially over time and contributed substantially (78%) to changes in abundance over the long‐term study, with minor contributions from reproduction and unstable stage structure.
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- Award ID(s):
- 2209765
- PAR ID:
- 10566721
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Ecology Letters
- Volume:
- 27
- Issue:
- 12
- ISSN:
- 1461-023X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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