Table 4.

Predicted and observed effects of prey dynamics on family structure in 146 arctic fox (Vulpes lagopus) litters

Prey dynamics	Food abundance	Predation pressure	Predictions of the resource dispersion hypothesis	Cost–benefit of accepting joiners according to Hersteinsson’s model	Joiner perspective	Proportion complex families	Observation
Low year	Low	Low	Low tolerance to joiners	Low	[Unclear]	–	[Lack of data as non-breeding foxes are difficult to observe]
Increase year	Medium/high	Low	Moderate or high tolerance to joiners	Moderately positive (Moderate cost and low predation)	Low incentive to join	8% (n = 78)	Few litters with joiners, but candidate joiners are limited (few yearlings)
Peak year	High	Low	High tolerance to joiners	Moderately positive (Low cost, low predation)	Moderate incentive to join	28% (n = 50)	Prediction supported
Decrease year	High/low	High	Low tolerance to joiners, depending on timing	Positive (High cost, high predation)	Potentially strong incentive to join	44% (n = 18)	High proportion of litters with joiners, but few litters in total. No resolution to determine timing