Restoration and intensive management have no effect on evolutionary strategies

Abstract

The European bison Bison bonasus is the largest extant terrestrial mammal on the European continent; however, the species went extinct in the wild in 1919. Restoration started in 1929 in Poland's Białowież a Primeval Forest using captive individuals sourced from zoological gardens and breeding centres. Of the 7 founders, 2 individuals contributed 85% to the genetic make-up of the lowland line of the species. The Białowież a bison population numbered 820 in 2008, but very low genetic diversity and a high level of management have raised questions as to whether it still conforms to evolutionary predictions. We tested whether the sex ratio of European bison calves conformed to the Trivers-Willard hypothesis at the population level, i.e. whether it became increasingly female-biased as bison condition deteriorated following increased population density. We found that increased population density and reduced female body mass led to increasing female-biased calf sex ratios, whereas mast years (abundant food resources) corresponded to male-biased sex ratios. Despite the high degree of inbreeding and management, European bison are still responding as expected to variations in female body condition; however, the precautionary principle cautions managers of small populations that artificial selection can alter the evolutionary strategy of wildlife even though we did not detect this in the Białowież a bison population. KEY WORDS: Body condition · Local resource competition hypothesis · Maternal investment · Reproductive success · Sex ratio manipulation · Trivers-Willard hypothesis · European bison · UngulatesResale or republication not permitted without written consent of the publisher

Pattern of parasite egg shedding by European bison (Bison bonasus) in the Białowieża Primeval Forest, Poland

“…The invasion of a new, dangerous parasite in the endangered population of bison in the BPF is alarming in light of the observed decline in their physical condition and the increasingly female-biased calf sex ratio. This is as predicted by TriversWillard hypothesis and may be associated with an increase in parasitic load especially the invasive A. sidemi (Hayward et al 2011). In recent years, the presence of A. sidemi was confirmed genetically in cattle (Moskwa et al 2015).…”

Risk perception by endangered European bison Bison bonasus is context (condition) dependent

“…Despite the risk of starvation conservation managers perceive of European bison (Hayward et al 2011), there was a surprisingly large proportion of hay remaining at the end of winter (*58 % of available hay), even though a large amount is wasted during foraging through trampling etc. This suggests that the meadows surrounding Białowie_ za Primeval Forest may have provided sufficient food for the local bison herds to persist through the essentially average winter, in regard to temperature, duration and snow depth, of 2007-2008.…”

Movements of European bison (Bison bonasus) beyond the Białowieża Forest (NE Poland): range expansion or partial migrations?

“…Data on cows was from 1992 (first observations of mixed groups out of the forest) to 2010, whilst the data concerning bulls was divided into two periods. The first period is from 1964 to 1989 ( n  = 167), when the main part of the population (mixed groups and the majority of bulls) used the central part of the forest, had even calf sex ratio and exhibited a slow increase (Hayward et al 2011). In the second period from 1990 to 2010 ( n  = 562), the population began to rapidly increase that led to increased dispersal rates, decrease in female body condition and female-biased calf sex ratio (Hayward et al 2011).…”