Capercaillie breeding success in relation to forest habitat and predator abundance

Ecological theory suggests that along productivity gradients, abundances of organisms within trophic levels will increase in a stepwise pattern from producers to consumers. To test this theory I investigated changes in abundance of soil arthropods at three trophic levels: microphytophages, represented by Collembola, predacious mites (Acari) that feed on Collembola, and three groups of macroarthropods (spiders, ants, and centipedes) that were observed to feed on mites. Changes in abundance were monitored along a gradient in vegetation structure from grass to shrub to forest in the Canadian prairies. I controlled for temporal variation in abundance among years and surveys within a year. As predicted, (i) numbers of Collembola did not change with increases in productivity; (ii) mite numbers were greatest in the shrublands; and (iii) numbers of macroarthropod predators increased from grassland to shrubland, and there was a nonsignificant increase in numbers of spiders and centipedes in forest habitat. Contrary to predictions, macroarthropod numbers were not significantly greater in forest habitat, and ant numbers actually declined. Possible explanations for the lack of increase in macroarthropod predator abundance in the forest habitat with the greatest productivity include decreased ground-level humidity and greater abundance of macroarthropod predators and parasites in forest environments.

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Effects of habitat and introduced mammalian predators on the breeding success of Yellow-eyed Penguins Megadyptes antipodes, South Island, New Zealand

Pacific Conservation Biology ◽

10.1071/pc990016 ◽

1999 ◽

Vol 5 (1) ◽

pp. 16 ◽

Cited By ~ 7

Author(s):

Hiltrun Ratz ◽

Brian Murphy

Keyword(s):

New Zealand ◽

Breeding Success ◽

East Coast ◽

Marked Effect ◽

Forest Edge ◽

Introduced Predators ◽

Mammalian Predators ◽

Predator Abundance ◽

Breeding Seasons ◽

Predator Guild

The endemic Yellow-eyed Penguin Megadyptes antipodes is threatened by habitat loss and introduced predators on mainland New Zealand. Nine colonies in the Catlins (south-east coast of South Island) were studied to measure breeding success, penguin abundance, and predator abundance in three successive breeding seasons (1991/92 to 1993/94). Nest numbers increased in all nine colonies in the three years despite predation (probably by Stoats Mustefa erminea) being the most important cause of breeding failure. Larger colonies with higher breeding success were in small gullies with limited shrubs and bushes rather than in the most intact mature forest colonies hitherto assumed to be optimal habitat for the birds. Penguin nests were concentrated near the forest edge, but predators were not, so the predation risk was not elevated near the forest edge. Fragmentation of the original forest habitat had no observable adverse effect on breeding success. Stoats dominated the predator guild, while Ferrets M. furo and Feral Cats Felis catus were rare. Trapping to kill predators early in the season had no marked effect on subsequent predation losses, but trapping intervention when a predation outbreak occurred curtailed further chick deaths. A simple population model predicts that Yellow-eyed Penguins populations will grow provided the average total chicks loss is less than 43% per season, or at least 0.85 chick per nest fledges each year. This requires predation losses to be less than 34%.

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Predation on artificial ground nests in relation to abundance of rodents in two types of forest habitats in the Tatra Mountains (southern Poland)

Wildlife Research ◽

10.1071/wr17134 ◽

2019 ◽

Vol 46 (3) ◽

pp. 205

Author(s):

Marcin Matysek ◽

Karol Zub ◽

Robert Gwiazda ◽

Filip Zięba ◽

Maciej Klimecki ◽

...

Keyword(s):

Small Mammals ◽

Breeding Success ◽

Myodes Glareolus ◽

Alternative Prey ◽

Tatra Mountains ◽

Forest Habitat ◽

Artificial Nests ◽

The Tatra Mountains ◽

Forest Habitats ◽

Ground Nesting

Context The breeding success of ground-nesting birds is strongly related to the predation rate. Many predators feed primarily on rodents when the densities of rodents are high and change to alternative prey (eggs or young birds) when the main prey populations decrease. Aims During a 3-year study, predation on an artificial nest was related to population dynamics of small mammals in coniferous and deciduous forests in the Tatra Mountains (western Carpathians). Methods Small mammals were captured using the live traps. In deciduous forest habitats, we placed 36 traps and, in coniferous forest habitats, we placed 18 traps. In total, 174 artificial nests imitating broods of hazel grouse (Tetrastes bonansia) were located randomly in both types of forest habitat between 2012 and 2014. Predators of the artificial nests were identified by camera-traps at 87 nests. Key results Most of the artificial nests were lost to predation by mammals. The most numerous species of rodents in both types of forest habitat were the yellow-necked mouse (Apodemus flavicollis) and the bank vole (Myodes glareolus). A significant decrease in the number of rodents was followed by a considerable increase of predation on artificial nests. There were no significant differences in the rates of predation between the two forest-habitat types. Conclusions Our results support the alternative prey hypothesis and suggest that the breeding success of ground-nesting birds in the forests of the Tatra Mountains varies strongly from year to year, depending on the abundance of rodents. Implications Increasing of rodents’ density may result in lower predation pressure on eggs of ground-nesting birds. This finding may help modify recommendations for conservationists and forest managers to optimize their effort to save populations of Galliformes.

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