DOI: 10.5061/dryad.vhhmgqnvg
title: Wild reindeer, wolf and moose population dynamics in Eastern Finland

description: Background. The alternative prey hypothesis describes the mechanism for
 apparent competition whereby the mortality of the secondary prey species
 increases (and population size 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.
description: Population counts in field 1996-2017, wild reindeer total counts
 from a helicopter in winter, calf/female ratio in reindeer based on field
 observations in autumn, moose sightings by hunting clubs, wolf estimates
 based on GPS telemetry and snow tracking.
description: For years when reindeer were not counted (1997, 2002, 2004), the
 population size was estimated as the mean of the population size before
 and after these years.