Improved viability of populations with diverse life-history portfolios

Abstract

A principle shared by both economists and ecologists is that a diversified portfolio spreads risk, but this idea has little empirical support in the field of population biology. We found that population growth rates (recruits per spawner) and life-history diversity as measured by variation in freshwater and ocean residency were negatively correlated across short time periods (one to two generations), but positively correlated at longer time periods, in nine Bristol Bay sockeye salmon populations. Further, the relationship between variation in growth rate and life-history diversity was consistently negative. These findings strongly suggest that life-history diversity can both increase production and buffer population fluctuations, particularly over long time periods. Our findings provide new insights into the importance of biocomplexity beyond spatio-temporal aspects of populations, and suggest that maintaining diverse life-history portfolios of populations may be crucial for their resilience to unfavourable conditions like habitat loss and climate change.

Figure 1.

Relationships between life-history diversity and recruits per spawner (RPS), and life-history diversity and the s.d. in RPS at five time periods in nine watersheds of Bristol Bay, Alaska. Measures of both life-history diversity and RPS are residuals from regressions that accounted for variation in spawner density in different regimes of the PDO. Lines indicate slopes of the relationship of life-history diversity and RPS. Open circle, Alagnak; open square, Egegik; small filled circle, Igushik; large filled circle, Kvichak; large filled triangle, Naknek; plus, Nushagak; filled square, Togiak; small filled triangle, Ugashik; open triangle, Wood.

Figure 2.

Slope of the relationship between residual life-history diversity and (a) residual RPS at five time periods and (b) s.d. in residual RPS at four time periods. Slopes were generated by the best mixed model (table 1) that included life-history diversity.