Does the Year-to-Year Variation in the Diet of Eagle and Ural Owls Support the Alternative Prey Hypothesis?

The alternative-prey hypothesis predicts that predation on goose eggs will be most severe the year following a lemming peak. We tested this by investigating how predators of goose eggs responded to lemming abundance on the Kent Peninsula, Nunavut, Canada, where nest success of white-fronted geese (Anser albifrons frontalis) and Canada geese (Branta canadensis hutchinsii) fluctuates widely. The main predators of both goose eggs and lemmings are arctic foxes (Alopex lagopus), glaucous gulls (Larus hyperboreus), and parasitic jaegers (Stercorarius parasiticus). Foxes responded functionally to lemming density: in prime goose-nesting areas they spent less time foraging during the peak lemming year than during the increase, and were seen foraging in prime nesting areas less often during the peak than during the decline. However, numbers of fox sightings in the study area during the nesting period did not differ significantly among years. The total response (functional × numerical) of gulls was lowest at the lemming peak and highest during the increase. The total response of parasitic jaegers did not vary significantly among years. Hence, we predicted that the number of nests lost to all predators combined should be lowest at the peak and possibly highest during the increase. During the 3 years of this study, loss of Canada goose nests was lowest at the peak but highest during the decline, and annual losses of white-fronted goose nests varied little. In cycles prior to this study, nest loss was high in declines but not particularly low during peaks. Several factors may alter the functional and numerical responses of predators, obscuring the simple pattern of nest loss predicted by the alternative-prey hypothesis.

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Diet variation of common buzzards in Finland supports the alternative prey hypothesis

Ecography ◽

10.1034/j.1600-0587.2001.240304.x ◽

2001 ◽

Vol 24 (3) ◽

pp. 267-274 ◽

Cited By ~ 21

Author(s):

Vitali Reif ◽

Risto Tornberg ◽

Sven Jungell ◽

Erkki Korpimäki

Keyword(s):

Alternative Prey ◽

Alternative Prey Hypothesis ◽

Diet Variation

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Patterns in grouse and Woodcock Scolopax rusticola hunting yields from central Norway 1901-24 do not support the alternative prey hypothesis for grouse cycles

Ibis ◽

10.1111/j.1474-919x.2006.00566.x ◽

2006 ◽

Vol 148 (4) ◽

pp. 678-686 ◽

Cited By ~ 7

Author(s):

VIDAR SELÅS

Keyword(s):

Alternative Prey ◽

Scolopax Rusticola ◽

Alternative Prey Hypothesis

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Calf/female ratio and population dynamics of wild forest reindeer in relation to wolf and moose abundances in a managed European ecosystem

PLoS ONE ◽

10.1371/journal.pone.0259246 ◽

2021 ◽

Vol 16 (12) ◽

pp. e0259246

Author(s):

Ilpo Kojola ◽

Ville Hallikainen ◽

Samuli Heikkinen ◽

Jukka T. Forsman ◽

Tuomas Kukko ◽

...

Keyword(s):

Population Size ◽

Prey Species ◽

Apparent Competition ◽

Alternative Prey ◽

Wolf Population ◽

Female Ratio ◽

Competition Hypothesis ◽

Alternative Prey Hypothesis ◽

Reindeer Population ◽

Eastern Finland

Background The alternative prey hypothesis describes the mechanism for apparent competition whereby the mortality of the secondary prey species increases (and population size decreases decreases) by the increased predation by the shared predator if the population size of the primary prey decreases. Apparent competition is a process where the abundance of two co-existing prey species are negatively associated because they share a mutual predator, which negatively affects the abundance of both prey Here, we examined whether alternative prey and/or apparent competition hypothesis can explain the population dynamics and reproductive output of the secondary prey, wild forest reindeer (Rangifer tarandus fennicus) in Finland, in a predator-prey community in which moose (Alces alces) is the primary prey and the wolf (Canis lupus) is the generalist predator. Methods We examined a 22-year time series (1996–2017) to determine how the population size and the calf/female ratio of wild forest reindeer in Eastern Finland were related to the abundances of wolf and moose. Only moose population size was regulated by hunting. Summer predation of wolves on reindeer focuses on calves. We used least squares regression (GLS) models (for handling autocorrelated error structures and resulting pseudo-R2s) and generalized linear mixed (GLMs) models (for avoidance of negative predictions) to determine the relationships between abundances. We performed linear and general linear models for the calf/female ratio of reindeer. Results and synthesis The trends in reindeer population size and moose abundance were almost identical: an increase during the first years and then a decrease until the last years of our study period. Wolf population size in turn did not show long-term trends. Change in reindeer population size between consecutive winters was related positively to the calf/female ratio. The calf/female ratio was negatively related to wolf population size, but the reindeer population size was related to the wolf population only when moose abundance was entered as another independent variable. The wolf population was not related to moose abundance even though it is likely to consist the majority of the prey biomass. Because reindeer and moose populations were positively associated, our results seemed to support the alternative prey hypothesis more than the apparent competition hypothesis. However, these two hypotheses are not mutually exclusive and the primary mechanism is difficult to distinguish as the system is heavily managed by moose hunting. The recovery of wild forest reindeer in eastern Finland probably requires ecosystem management involving both habitat restoration and control of species abundances.

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