Determinants of lifetime reproduction in female brown bears: early body mass, longevity, and hunting regulations

Abstract

Abstract. In iteroparous mammals, conditions experienced early in life may have longlasting effects on lifetime reproductive success. Human-induced mortality is also an important demographic factor in many populations of large mammals and may influence lifetime reproductive success. Here, we explore the effects of early development, population density, and human hunting on survival and lifetime reproductive success in brown bear (Ursus arctos) females, using a 25-year database of individually marked bears in two populations in Sweden. Survival of yearlings to 2 years was not affected by population density or body mass. Yearlings that remained with their mother had higher survival than independent yearlings, partly because regulations prohibit the harvest of bears in family groups. Although mass as a yearling did not affect juvenile survival, it was positively associated with measures of lifetime reproductive success and individual fitness. The majority of adult female brown bear mortality (72%) in our study was due to human causes, mainly hunting, and many females were killed before they reproduced. Therefore, factors allowing females to survive several hunting seasons had a strong positive effect on lifetime reproductive success. We suggest that, in many hunted populations of large mammals, sport harvest is an important influence on both population dynamics and life histories.

Maternal Natal Environment and Breeding Territory Predict the Condition and Sex Ratio of Offspring

“…The condition and sex ratio of offspring were also associated with the quality of a female’s current breeding territory. Territory quality and resource abundance during development can affect life-history trajectories in a variety of taxa (Haywood and Perrins 1992; Lindström 1999; Millon et al 2011; Douhard et al 2013; Zedrosser et al 2013; but see also Drummond and Ancona 2015). For example, in great tits ( Parus major ), the long-term survival and reproductive success of neonates are negatively correlated with the altitude and positively correlated with the size of the territories on which they are reared, and to a greater extent for male than for female offspring (Wilkin and Sheldon 2009).…”

The quantification of reproductive hormones in the hair of captive adult brown bears and their application as indicators of sex and reproductive state

“…Our interest in reproduction is because of its importance as an attribute of health (i.e. reproduction may be suppressed or cease when health is compromised) and biological fitness in individual animals (Eberhardt, 2002; Zedrosser et al ., 2013), and because it is required as a measurement to estimate reproductive rates at the population level (Garshelis et al ., 2005). Our specific research objectives were to:

Develop laboratory procedures and establish performance specifications to quantify reproductive steroid hormone (testosterone, progesterone, estradiol) concentrations in brown bear hair.

Determine if the hair concentrations of reproductive hormones, as well as cortisol, another steroid hormone, are correlated with each other.

Evaluate if the method of hair collection, plucked which provides samples that include follicles, or shaved which provides samples composed only of hair shafts, is related to the concentrations of reproductive hair hormones in a consistent manner (e.g.

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Can concentrations of steroid hormones in brown bear hair reveal age class?

“…We recognized, however, that the median age threshold could also be higher, because of variation among individual bears in the timing of sexual maturation (Schwartz et al , 2003). In this regard, several studies of brown bears in the study areas from where we obtained samples have also used 4 or 5 years as the adult-age threshold (Zedrosser et al , 2013; Gosselin et al , 2015; Sorensen et al , 2015; Kite et al , 2016). …”