Demographic routes to variability and regulation in bird populations.
There is large interspecific variation in the magnitude of population fluctuations, even among closely related species. The factors generating this variation are not well understood, primarily because of the challenges of separating the relative impact of variation in population size from fluctuations in the environment. Here, we show using demographic data from 13 bird populations that magnitudes of fluctuations in population size are mainly driven by stochastic fluctuations in the environment. Regulation towards an equilibrium population size occurs through density-dependent mortality. At small population sizes, population dynamics are primarily driven by environment-driven variation in recruitment, whereas close to the carrying capacity K, variation in population growth is more strongly influenced by density-dependent mortality of both juveniles and adults. Our results provide evidence for the hypothesis proposed by Lack that population fluctuations in birds arise from temporal variation in the difference between density-independent recruitment and density-dependent mortality during the non-breeding season.
Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
Bernt-Erik
BE
Sæther
Department of Biology, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
Vidar
V
Grøtan
Department of Mathematical Sciences, Centre for Biodiversity Dynamics, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway.
Steinar
S
Engen
Department of Zoology, University of Oxford, South Parks Road, OX1 3PS Oxford, UK.
Tim
0000-0001-9371-9003
T
Coulson
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA.
Peter R
PR
Grant
Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), Wageningen, The Netherlands.
Marcel E
ME
Visser
Department of Biology, University Hill, University of Turku, FI-02700 Turku, Finland.
Jon E
JE
Brommer
Department of Ecology and Evolutionary Biology, Princeton University, Princeton, New Jersey 08544, USA.
B
B
Rosemary Grant
Department of Animal Ecology, Evolutionary Biology Centre, Uppsala University, Norbyvägen 18D, SE-752 36 Uppsala, Sweden.
Lars
L
Gustafsson
Department of Animal &Plant Sciences, University of Sheffield, Western Bank, Sheffield S10 2TN, UK.
Ben J
BJ
Hatchwell
Aurebekksveien 61, NO-4516 Mandal, Norway.
Kurt
K
Jerstad
Department of Biosciences, Environmental and Marine Biology, Åbo Akademi University, FI-02700 Turku, Finland.|Coastal Zone Research Team, Novia University of Applied Sciences, Raseborgsvägen 9, FI-10600 Ekenäs, Finland.
Patrik
P
Karell
Bird Ecology Unit, Department of Biosciences, University of Helsinki, FI-00014 Helsinki, Finland.
Hannu
H
Pietiäinen
Department of Ecology and Evolution, Biophore, University of Lausannne, 1024 Lausanne, Switzerland.
Alexandre
A
Roulin
Department of Ecology and Natural Resource Management, Norwegian University of Life Sciences, NO-1432, Ås, Norway.
Ole W
OW
Røstad
Centre d'Etudes Biologiques de Chizé, CNRS-UPR 1934, 79360 Villiers en Bois, France.
Henri
H
Weimerskirch
D000818:Animals; D000864:Antarctic Regions; D044822:Biodiversity; D001717:Birds / Q000502:physiology*; D017753:Ecosystem; D005260:Female; D005828:Genetics, Population; D008297:Male; D015233:Models, Statistical; D011156:Population Density; D011157:Population Dynamics; D011158:Population Growth; D013045:Species Specificity; D013269:Stochastic Processes; D020305:Strigiformes; D013997:Time Factors