Evol Ecol Res 17: 355-372 (2016)     Full PDF if your library subscribes.

Consumptive and non-consumptive effects of predation
by introduced northern pike on life-history traits in threespine stickleback

David C. Heins¹, Helen Knoper¹ and John A. Baker²

¹Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, Louisiana, USA and  ²Department of Biology, Clark University, Worcester, Massachusetts, USA

Correspondence: D.C. Heins, Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, LA 70118, USA.
e-mail: heins@tulane.edu

ABSTRACT

Background: Non-native, predatory northern pike (Esox lucius) are spreading into lakes of south-central Alaska and were illegally introduced into Scout Lake in 2001 or 2002. Pike preyed on native threespine stickleback (Gasterosteus aculeatus) in the lake, subjecting them to higher mortality rates.

Hypotheses: Life-history theory predicts evolutionary changes in threespine stickleback females arising from consumption by predators, including reduced body size, earlier age of reproduction, increased reproductive effort (greater clutch mass and clutch size), and, under some conditions, smaller offspring. Alternatively, energetically costly, non-consumptive predation-risk effects resembling food limitation – such as predator avoidance, reduced foraging efficiency, and chronic stress – might cause phenotypically plastic responses inconsistent with life-history theory.

Methods: We measured changes in length, body mass, clutch mass, clutch size, and egg mass during an 11-year (1999–2009) study. In analyses of clutch mass, clutch size, and egg mass, we used body mass to correct for female size.

Results: Consistent with predictions from life-history theory, the mean size and age of reproducing females declined, with one decline in size following the initial pike introduction and another after sport-fish stocking of salmonids was discontinued. The principal age at reproduction gradually shifted from two years to one year of age, with few females surviving to reproduce in a second year. Clutch mass and clutch size declined, suggesting non-consumptive predation-risk effects resembling those of nutrient deprivation. Egg mass showed an overall decline, with a moderate, temporary increase near the end of the study period.

Keywords: food limitation, invasive species, nutrient deprivation, physiological stress, predation risk, reproduction, threespine stickleback.

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