# Comparative analyses of life-history strategies in Asiatic and African wild asses using a demographical approach.

Abstract. Trade-offs such as the ones between reproduction and longevity or present and future reproduction are believed to shape reproductive patterns. We here used zoo data to investigate trade-offs and life histories in four taxa of Asiatic (Equus hemionus ssp.) and African wild asses (Equus africanus ssp.). All taxa showed even in captivity peak birth rates during the periods of highest food availability in their natural environments. Sex-specific survival rates with females living longer than males were evident in kulan and onager but not in kiang and Somali wild ass, pointing towards different life-history strategies even among closely related taxa. Females achieved their highest reproductive output earlier in life than males, which is typical for polygynous mating systems. Offspring number and longevity were positively rather than negatively correlated. Taken together evidence for reproductive trade-offs was weak, though the length of the reproductive period was negatively related to birth rates within the reproductive period. Birth intervals increased with female age, probably reflecting detrimental effects of senescence. Despite several limitations, zoo data seem to be useful to better understand the reproductive biology of endangered, rare or cryptic species.Key words: life-history, trade-off, post-reproductive phase, reproductive phase, birth interval

Introduction

Life histories comprehend all life stages of an individual from birth to death, including age- or stage-specific patterns of reproduction, survival and death. A major objective is to understand how these traits were formed by natural selection in an evolutionary comparative way (Stearns 1989, Roff 2002, Flatt & Heyland 2011). Key life history traits are for instance longevity, age at first reproduction, number and quality of offspring or parental care (Stearns 1989, Roff2002, Flatt & Heyland 2011). All these traits are thought to be constrained by trade-offs, as limited resources can only be allocated once and, consequently, augmenting one feature will have negative effects on others (Roff 2002, Stearns 1989, Zera & Harshman 2001, Flatt & Heyland 2011). A classical trade-off is the one between present and future reproduction, meaning that an increase in present reproduction can only be achieved at the expense of reduced future reproduction opportunities, for instance because it reduces longevity (Stearns 1989, Zera & Harshman 2001, Roff 2002). Longevity, however, may strongly affect individual fitness especially in iteroparous, long-lived species due to positive correlations with reproductive output (Newton 1989, Stearns 1989, Zera & Harshman 2001). Hence, longevity and reproduction are expected to be traded off against each other, although positive correlations have been repeatedly found as high-quality individuals may be able to strongly invest into both (Bell & Koufopanou 1986, Clutton-Brock 1988, Newton 1989). Thus, the above trade-off warrants an optimal distribution of reproductive events throughout lifetime, including birth intervals and birth rates. Birth intervals are regarded as an indicator of the mother's performance, with high-quality females being able to afford short intervals (Duncan et al. 1984). Resource-allocation trade-offs may further be modulated by other factors such as population density. This is because density increases competition, typically reducing food availability and storage reserves in turn reducing reproductive potential (Fowler 1987, Stewart et al. 2005).

Though understanding life-history trade-offs is obviously important, appropriate data are often not available. This is especially true for cryptic, rare or endangered species. Against this background we here make use of zoo data gathered for four highly endangered equids, for which hardly any other data are available. We investigate three Asiatic wild ass subspecies (kulan, Equus hemionus kulan, onager, E. h. onager, and kiang, E. h. holdereri) and the African Somali wild ass (Equus africanus somalicus) to get some insights into their life histories. Striking advantages of zoo data are their accuracy and their availability even for endangered, non-domestic species (e.g. Pohle 1971-2014, Pohle 1973-2014, Pelletier et al. 2009). Using such data may not only enhance our general understanding of life-history trade-offs, but also breeding protocols and thus offspring production aiding reintroduction or conservation projects for these highly endangered equids (Nowak 1999, Bahloul et al. 2001, Feh et al. 2001, Moehlmann 2005).

Specifically, we address the following questions here: 1) Do births show age-specific variation and seasonal patterns even under beneficial zoo conditions? 2) Are reproduction and longevity traded-off against each other or are they positively correlated? 3) Are there sex differences in survival patterns, which may reflect differential investment into reproduction? 4) Are high offspring numbers/birth rates associated with lower offspring quality? 5) Do birth intervals dependent on female age as a matter of ongoing senescence, or the sex of the previous offspring due to differential maternal investment?

Material and Methods

Study organisms

We here studied three Asiatic wild asses (Equus hemionus), namely kulan (E. h. kulan Groves & Mazak, 1968), onager (E. h. onager Boddaer, 1785), and kiang (E. h. holdereri Moorcroft, 1841), as well as the African Somali wild ass (Equus africanus somalicus Sclater, 1885). Asiatic wild asses live in (semi-)desert and steppe habitats of Russia, Turkmenia and Kazakhstan (kulan), Iran (onager), and Southern China (kiang; Groves & Mazak 1968, Nowak 1999, Oakenfull et al. 2000). Concomitantly, they are able to survive extended periods of time with minimum food and water supply (Klingel 1998, Nowak 1999). Adult females and immatures live in groups of up to 400 individuals and are led by an old female, while adult males tend to live alone (Klingel 1998, Nowak 1999). Kulan and onager are highly endangered due to poaching, habitat destruction, and competition with domestic animals (Dathe 1971, Saltz & Rubenstein 1995, Bahloul et al. 2001, Moehlmann 2005). Kulans mainly persist in (semi-)wild populations in central Asia, and onagers are nowadays restricted to a few protected sites in Iran (Klingel 1998, Bahloul et al. 2001, Moehlmann 2005). Compared with both above taxa, the kiang seems to be less endangered (Nowak 1999, Moehlmann 2005). Historically, Equus africanus was distributed throughout northern Africa, but is now critically endangered and restricted to Ethiopia, Eritrea, and Somalia (Lang & Lehmann 1972, Dathe 1973, Gippoliti 2014). The Somali wild ass also inhabits (semi-) arid bush- and grassland.

[FIGURE 1 OMITTED]

Data acquisition and analyses

Because of their high endangerment, the World Association of Zoos and Aquaria decided to establish international studbooks for Asiatic (Pohle 1971-2014) and African wild asses (Pohle 1973-2014). These studbooks include data on > 1800 kulan, 900 onager, 350 kiang, and 620 Somali wild ass individuals. The extant zoo populations were founded by 130 kulan, 55 onager, 10 kiang, and 11 Somali wild asses (Pohle 1971-2014, Pohle 1973-2014). The data collected in the studbooks include sex, date of birth, date of death, transfer dates, locations, and the identity of parents for all individuals kept in zoos at a global scale. These data form the basis for all further analyses (cf. Table 1). We calculated lifespan as the period between birth and death, and post-reproductive phase as the period between the birth of the last offspring and the individual's death. Only data from animals that 1) had already died, 2) originate from the northern hemisphere (because of possible climatic and light cycle influences on mortality rates), and 3) from institutions where no management, culling or contraception as it was the case in the past were applied were included in subsequent analyses. Note that most of the data presented here stem from 1955-1995 i.e. the period during which males and females were typically kept together and unconstrained reproduction was allowed.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

Statistical analyses

All statistical tests have been computed using SPSS 13.0 or Minitab 16. The distribution of births in relation to season (month, Fig. 1) and in relation to male and female age across species and sexes (Fig. 2) were tested against each other using Kolmogorov-Smirnov tests. Survival curves of males and females were statistically compared with Wilcoxon-Gehan tests (Fig. 3). Heritability of longevity was estimated as the slope of mid-parent versus mid-offspring regressions (Table 2). To investigate effects of 1) reproductive traits on longevity (Table 3), 2) reproductive traits on the length of the reproductive and post-reproductive phase, respectively (Table 4), and 3) the impact of age at reproduction on birth intervals (Table 5) we used linear mixed models including individual identity (ID), keeping and density (if applicable) as random (or repeated) covariates. We calculated "individual density" as the median group size experienced by a given individual during its entire life span, keeping as the location where the animal lived the majority of its lifespan and ID as the identity number of a certain individual.

Results

Births in relation to season and age

In terms of the distribution of birth rates across the season, all four taxa showed similar patterns with peaks between May and July (Fig. 1). In Somali wild asses, though, births appeared to be more scattered throughout the season than in the other three taxa. Sex differences, with birth rates peaking at a later age in males than in females, were significant in all four taxa (Kolmogorov-Smirnov test: all P-values < 0.001; Fig. 2). Accordingly, first reproduction took place at an age of three years in kulan males, two years in kulan females, three years in onager males, two years in onager females, two years in kiang males, three years in kiang females, four years in male and two years in female Somali wild asses. Birth distributions in relation to age for males were very similar across species, the only significant difference occurring between kiang and Somali wild ass (Z = 5.6, P < 0.001), with the distribution being more peaked in kiang. The same pattern of a more peaked birth distribution, being significantly different from all other species (all P-values < 0.004), also prevailed in female kiang. Furthermore, the distribution of births in kulan females differed from those in onager and Somali wild ass (both P-values < 0.001). All other comparisons were non-significant.

Sex- and species-specific variation in survival rates Mean longevity was 5.1 [+ or -] 0.3 and 8.7 [+ or -] 0.4 years in kulan males and females, 5.7 [+ or -] 0.4 and 9.4 [+ or -] 0.5 years in onager males and females, 5.8 [+ or -] 0.6 and 6.6 [+ or -] 1.0 years in kiang males and females, and 6.8 [+ or -] 0.8 and 6.5 [+ or -] 1.0 years in male and female Somali wild asses. Accordingly, kulan (Wilcoxon-Gehan: 24.2, df = 1, P < 0.001) and onager females (Wilcoxon-Gehan: 20.6, P < 0.001) showed significantly higher survival rates than their male counterparts, which was not the case in kiang (P = 0.431) and Somali wild ass (P = 0.660; Fig. 3). Across species, male survival rates did not differ significantly (all P-values > 0.3). In contrast, kulan and onager females had significantly higher survival rates than kiang and Somali wild ass females (kulan vs. kiang: Wilcoxon-Gehan: 7.2, P = 0.007; kulan vs. Somali wild ass: Wilcoxon-Gehan: 5.4, P = 0.021; onager vs. kiang: Wilcoxon-Gehan: 6.3, P = 0.012; onager vs. Somali wild ass: Wilcoxon-Gehan: 5.3, P = 0.022; all other combinations non-significant: P > 0.6). Throughout, mortality rates were not significantly affected by male or female density (after Bonferroni correction; range of P-values 0.022-0.983, n = 16 analyses). Parent-offspring regressions indicated significant heritability for longevity in kulan and onager and an according tendency in kiang (Table 2).

Reproduction and longevity

Mean offspring number per breeding individual was 7 [+ or -] 0.5 in kulan males and 4 [+ or -] 0.2 in kulan females, 7 [+ or -] 0.6 and 4 [+ or -] 0.2 in onager males and females, 7 [+ or -] 1.3 and 3 [+ or -] 0.3 in kiang males and females, and 9 [+ or -] 1.3 and 4 [+ or -] 0.3 in Somali wild ass males and females. Maximum offspring number amounted to 42 and 16 in kulan males and females, 36 and 13 in onager males and females, 28 and 10 in kiang males and females, and 38 and 10 in Somali wild ass males and females. Offspring number was significantly positively related to longevity in kulan males and females, onager males and females, and Somali wild ass males and females, but not in kiang males and females, while birth rate was not significantly related to longevity throughout (Table 3).

The length of reproductive phase (Table 4) correlated significantly positively with longevity and offspring number in all taxa, and with birth rate throughout the entire lifespan in two out of four taxa. Reproductive phase tended to be negatively related to post-reproductive phase in kulan and onager, and to birth rate within the reproductive phase in one out of four cases (plus two according tendencies). No significant relations were found between offspring surviving > 100 days and the length of the reproductive phase. Age at first reproduction was significantly negatively related to the length of the reproductive phase in kiang only. Throughout, effects of female identity, keeping, and density had no significant influence.

Similar to above, the length of the post-reproductive phase was significantly positively related to female longevity in all four taxa (Table 4). Additionally, birth rate throughout the entire lifespan was significantly negatively associated with the length of the post-reproductive in kulan and onager. Relationships between other reproductive traits and the length of the post-reproductive were non-significant throughout, as were effects of female identity, keeping, and density. Birth intervals increased significantly with age in all four taxa, while the sex of the previous offspring had no significant impact (Table 5). Effects of individual ID were significant throughout, while those of keeping or density were not. Regarding the relationship between birth rate throughout the entire lifespan and the percentage of offspring surviving > 100 days, a significantly negative relationship was found in kulan females only ([F.sub.1,209] = 15.8, P < 0.0001; all other P-values > 0.46).

Discussion

Births in relation to season and age

All four taxa showed a seasonal distribution of births peaking in spring and early summer (May to July), though the distribution appeared to be less peaked in Somali wild asses compared with the other taxa. Asiatic wild asses live in Asian regions where rainfalls peak usually in spring. Thus, the majority of young are born 1-2 months after peak rainfall, i.e. within the period of highest food availability (Siegmund 2006). At the same time, females are in good condition within this period of time (Prins 1996). The Przewalski horse (Equus przewalski), a related equid with similar biology, also shows a peak of births between May and July (Volf 1996). In Somalia and Eritrea, the home of the Somali wild ass, most rain falls in May, October and November, which may explain the more scattered birth pattern. Anyway, our data clearly suggest that the wild asses studied are well synchronized with the ecological conditions within their natural environments, despite being kept under favourable conditions throughout the year. Compared with females, males are typically older when they reproduce for the first time. This pattern is characteristic for polygynous mating systems, in which males compete directly for access to females (sexual bimaturism: Badyaev 2002, Taborsky & Brockmann 2010). Accordingly, males reach their highest reproductive output later than females.

Sex- and species-specific variation in survival rates

In kulan and onager but not in kiang and Somali wild ass, females lived longer than males as has been also found in other mammals and birds (Promislow 1992). This difference is caused by females of both former taxa living longer than their male counterparts as well as kiang and Somali wild ass females, while male longevity did not differ significantly across taxa throughout. A shorter male lifespan may originate from the need to monopolize females, which depends on resource holding potential (i.e. is strength; Klingel 1977, Badyaev 2002, Taborsky & Brockmann 2010). Therefore, males have to accumulate more body mass and, thus, need more energy (Clutton-Brock et al. 1997, Badyaev 2002, Taborsky & Brockmann 2010). Nevertheless, they are typically able to monopolize females in their "best years" only, reducing benefits of living particularly long. In females, in contrast, longevity is often positively related to offspring number (see below). Why kiang and Somali wild ass did not show sexual differences in mortality rates is currently unclear, while the very similar patterns found for onager and kulan may reflect their close relatedness. Both taxa can hardly be distinguished phenotypically and are fully hybridisable (Dathe 1971). Longevity showed a low heritability in kulan and onager and an according tendency in kiang, which is typical for fitness-related traits (Falconer 1981, Kruuk et al. 2000, Akesson et al. 2008).

Reproduction and longevity

High reproductive investment and longevity are often believed to be traded-off against each other (Clutton-Brock 1988, Newton 1989, Kirkpatrick & Turner 2007). In our study, though, longevity and the length of the reproductive period were positively related (except in kiang for the correlation with longevity). Such patterns of positive rather than negative correlations have been found repeatedly (Bell & Koufopanou 1986, Clutton-Brock 1988, Newton 1989). They presumably reflect that individuals getting older have more time to produce offspring, and that high-quality individuals may afford to strongly invest into both longevity and reproduction (Bell & Koufopanou 1986, Clutton-Brock 1988, Newton 1989). In this context, it should be noted that birth rate was not related to longevity, showing that birth rates were similar in animals differing in lifespan, corroborating the first conclusion above. Additionally, the length of the reproductive period was positively related to birth rate throughout the entire lifespan in two taxa, supporting the second conclusion.

Reproductive and post-reproductive phase jointly contributed to longevity (Cohen 2004, Turbill & Ruf 2010), although the two were negatively correlated in two taxa. A prolonged post-reproductive phase may have, e.g. in humans, benefits for the group (Judge & Carey 2000, Reznick et al. 2006, Lahdenpera et al. 2014), which may also apply to equids (Klingel 1977, 1998, Volf 1996). Interestingly, the length of the reproductive period and birth rate within the reproductive period (i.e. mean birth intervals) were negatively correlated in three taxa, suggesting a trade-off between the two. Thus, it appears that a fixed number of offspring can be produced within a longer or shorter time period, but that high birth rates cannot be sustained over longer periods (Grange et al. 2004, Barnier et al. 2012).

Birth intervals depend mainly on the delay of conception after birth (Puschmann 2003, Barnier et al. 2012). In plains zebra (Equus quagga ssp.) a longer birth interval after male than female offspring has been found, indicating that sons may be more costly than daughters (Clements et al. 2011, Barnier et al. 2012), based on a higher demand for food and care (Trivers & Willard 1973, Cameron & Linklater 2000, Barnier et al. 2012). In our study, however, such relationships were not evident throughout. However, birth interval increased with increasing female age, suggesting detrimental effects of ongoing senescence (Clutton-Brock 1984).

Conclusions

We here used zoo-derived data to explore life-history trade-offs and reproductive patterns in four equid taxa. Captive populations experience highly favourable conditions and are largely relieved from seasonal constraints (e.g. food, climate, predators). Even though birth rates clearly showed seasonal variation matching the food availability in their natural habitats. We therefore assume that data derived from zoo populations may be at least to some extent useful to understand animal life histories. Interestingly, females lived longer than males in two of the taxa only, indicating divergent life-history strategies even amongst these closely related taxa. Offspring number and longevity were positively rather than negatively correlated, indicating that high-quality individuals can afford to invest into both at a time. Evidence for trade-offs, in contrast, was very weak. As an example, the length of the reproductive period was negatively related to birth rate within the reproductive period.

This may suggest that a fixed number of offspring can be produced within a longer or shorter period, but that high birth rates cannot be sustained over extended time periods. Despite several limitations, zoo data seem to be useful to better understand the reproductive biology of endangered, rare or cryptic species.

Acknowledgements

We would like to thank Claus Pohle, manager of the international studbook for Asiatic and African wild asses since 1966, Dr. Bernhard Blaszkiewitz, director emeritus, Berlin, and Dr. Frank Brandstatter, director of Dortmund Zoo, for their support and valuable discussions on mammal life histories, Dr. Doris Schuhmann and Bodo Brandt for linguistic revisions, and Sebastian Graf for kind help with statistics and software.

Literature

Akesson M., Bensch S., Hasselquist D. et al. 2008: Estimating heritabilities and genetic correlations, comparing the "animal model" with parent-offspring regression using data from a natural population. PLoS ONE 1: e739.

Badyaev A.A. 2002: Growing apart. An ontogenetic perspective on the evolution of sexual size dimorphism. Trends Ecol. Evol. 17: 369-378.

Bahloul K., Pereladova O.B., Soldatova N. et al. 2001: Social organization and dispersion of introduced kulans (Equus hemionus kulan) and Przewalski horses (Equus przewalski) in the Bukhara Reserve, Uzbekistan. J. Arid Environ. 47: 309-323.

Barnier F., Grange S., Ganswindt A. et al. 2012: Interbirth interval in zebras is longer following the birth of male foals than after female foals. Acta Oecol. 42:11-15.

Bell G. & Koufopanou V. 1986: The cost of reproduction. Oxf. Surv. Evol. Biol. 3: 83-131.

Cameron E.Z. & Linklater W.L. 2000: Individual mares bias investment in sons and daughters in relation to their condition. Anim. Behav. 60: 359-367.

Clements M.N., Clutton-Brock T.H., Albon S.D. et al. 2011: Gestation length variation in a wild ungulate. Funct. Ecol. 25: 691-703.

Clutton-Brock T.H. 1984: Reproductive effort and terminal investment in iteroparous animals. Am. Nat. 123: 212-229.

Clutton-Brock T.H. 1988: Reproductive success. Studies of individual variation in contrasting breeding systems. University of Chicago Press, Chicago, U.S.A.

Clutton-Brock T.H., Rose K.E. & Guinness F.E. 1997: Density-related changes in sexual selection in red deer. Proc. R. Soc. Lond. B 264:1509-1516.

Cohen A.A. 2004: Female post-reproductive lifespan, a general mammalian trait. Biol. Rev. 79: 733-750.

Dathe H. 1971: Introduction for the setting up of international studbook of the Asiatic wild ass. In: Pohle C. (ed.), International studbook for Asiatic wild asses, 1st ed. Berlin: 8-13.

Dathe H. 1973: Introduction for the setting up of international studbook of the African wild ass. In: Pohle C. (ed.), International studbook for African wild asses. 1st ed. Berlin: 6-7.

Duncan P., Harvey P.H. & Wells S.M. 1984: On lactation and associated behaviour in a natural herd of horses. Anim. Behav. 32:255-263.

Falconer D.S. 1981: Introduction to quantitative genetics, 2nd ed. Longman, London.

Feh C., Munkhtuya B., Enkhbold S. & Sukhbaatar T. 2001: Ecology and social structure of the Gobi khulan (Equus hemionus subsp.) in the Gobi B National Park, Mongolia. Biol. Conserv. 101: 51-61.

Flatt T. & Heyland A. 2011: Mechanisms of life history evolution. The genetics and physiology of life history traits and trade-offs. Oxford University Press, Oxford.

Fowler C.W. 1987: A review of density dependence in populations of large mammals. Curr Mammal. 1: 401-441.

Gippoliti S. 2014: The forgotten donkey's history. Remarks on African wild asses of the Giardino Zoologico in Rome and their relevance for Equus africanus (von Heuglin & Fitzinger, 1866) taxonomy and conservation. Zool. Gart. 83: 146-153.

Grange S., Duncan P., Gaillard J.M. et al. 2004: What limits the Serengeti zebra population? Oecologia 140: 523-532.

Groves C.P. & Mazak V. 1968: On some taxonomic problems of Asiatic wild asses with the description of a new subspecies (Perissodactyla; Equidae). Z. Saugetierkd. 32: 321-355.

Judge D.S. & Carey J.R. 2000: Postreproductive life predicted by primate patterns. J. Gerontol. A 55: B201-B209.

Kirkpatrick J.F. & Turner A. 2007: Immunocontraception and increased longevity in equids. Zoo Biol. 26: 237-244.

Klingel H. 1977: Observations on social organization and behaviour of African and Asiatic wild asses (Equus africanus and E. hemionus). Ethology 44: 323-331.

Klingel H. 1998: Observations on social organization and behaviour of African and Asiatic wild asses (Equus africanus and Equus hemionus). Appl. Anim. Behav. Sci. 60: 103-113.

Kruuk L.E.B., Clutton-Brock T.H., Slate J. et al. 2000: Heritability of fitness in a wild mammal population. Proc. Natl. Acad. Sci. U.S.A. 97: 698-703.

Lahdenpera M., Mar K.U. & Lummaa V. 2014: Reproductive cessation and post-reproductive lifespan in Asian elephants and pre-industrial humans. Front. Zool. 11: 54.

Lang E.M. & Lehmann E. 1972: Wildesel in Vergangenheit und Gegenwart. Zool. Gart. 41: 157-167.

Moehlman P.D. 2005: Endangered wild equids. Sci. Am. 292: 86-93.

Newton I. 1989: Lifetime reproductive success in birds. Academic Press, London.

Nowak R.M. 1999: Walker's mammals of the world. Smithsonian Institution Press, Washington.

Oakenfull E.A., Lim H.N. & Ryder O.A. 2000: A survey of equid mitochondrial DNA, implications for the evolution, genetic diversity and conservation of Equus. Conserv. Genet. 1: 341-355.

Pelletier F., Reale D., Watters J. et al. 2009: Value of captive populations for quantitative genetics research. Trends Ecol. Evol. 24: 263-270.

Pohle C. 1971-2014: International studbook for Asiatic wild asses, vol. 1-16. Berlin.

Pohle C. 1973-2014: International studbook for African wild asses, vol. 1-41. Berlin.

Prins H.H. 1996: Ecology and behaviour of the African buffalo. Social inequality and decision making. Wildlife ecology and behaviour series 1, Chapman & Hall, London.

Promislow D.E.L. 1992: Senescence in natural populations of mammals, a comparative study. Evolution 45: 1869-1887.

Puschmann W. 2003: Zootierhaltung. Saugetiere. Harri Deutsch Verlag, Frankfurt am Main.

Reznick D., Bryant M. & Holmes D. 2006: The evolution of senescence and post-reproductive lifespan in guppies (Poecilia reticulata). PLoS Biol. 4: e7.

Roff D.A. 2002: The evolution of life histories, 7th vol. Sinauer, New York.

Saltz D. & Rubenstein D.I. 1995: Population dynamics of a reintroduced Asiatic wild ass (Equus hemionus) herd. Ecol. Appl. 5: 327-335.

Siegmund A. 2006: Diercke spezial, Angewandte Klimageographie. Klimatabellen und ihre Auswertung. Westermann, Braunschweig.

Stearns S.C. 1989: Trade-offs in life-history evolution. Funct. Ecol. 3: 259-268.

Stewart K.M., Bowyer R.T., Dick B.L. et al. 2005: Density-dependent effects on physical condition and reproduction in North-American elk, an experimental test. Oecologia 143: 85-93.

Taborsky M. & Brockmann H.J. 2010: Alternative reproductive tactics and life history phenotypes. In: Kappeler P. (ed.), Animal behaviour, evolution and mechanisms. Springer, Berlin: 537-586.

Trivers R.L. & Willard D.E. 1973: Natural selection of parental ability to vary the sex-ratio of offspring. Science 191: 249-263.

Turbill C. & Ruf T. 2010: Senescence is more important in the natural lives of long- than short-lived mammals. PLoS ONE 5: e12019.

Volf J. 1996: Das Urwildpferd Equus przewalski. Neue Brehm Bucherei 249. Westarp Wissenschaften, Magdeburg.

Zera A.J. & Harshman L.G. 2001: The physiology of life history trade-offs in animals. Annu. Rev. Ecol. Evol. Syst. 32: 95-126.

Benjamin IBLER (1,2*) and Klaus FISCHER (1)

(1) Zoological Institute and Museum, University of Greifswald, Loitzer Str. 26, D-17489 Greifswald, Germany; e-mail: benjamin. ibler@gmx. de

(2) City of Dortmund, Dortmund Zoological Garden, Mergelteichstr. 80, D-44225 Dortmund, Germany

Received 4 January 2017; Accepted 5 June 2017

(*) Corresponding Author

Table 1. Summary of parameters (including categories and units) used to investigate life-history patterns in Asiatic and African wild asses. Parameter Categories/units Sex male, female Longevity (days) Age at first reproduction (days) Length of reproductive phase (days) Length of post-reproductive phase (days) Offspring number number Birth interval (days) Birth rate per year throughout the entire lifespan (number/year) Birth rate per year throughout the reproductive phase (number/year) Percentage of offspring surviving > 100 days (%) Mean longevity of offspring (days) Table 2. Results of parent-offspring regressions to estimate the heritability of longevity. Heritabilities were estimated as the slope of midparents versus mid-offspring linear regressions. Only P-values < 0.025 are significant after applying a sequential Bonferroni correction. Longevity Slope F P n Kulan 0.11 8.0 0.005 333 Onager 0.20 17.0 < 0.001 216 Kiang 0.20 4.2 0.047 46 Somali wild ass 0.05 0.2 0.656 43 Table 3. Linear mixed models for the effects of offspring number and birth rate, respectively, on breeding male and female longevity in kulan, onager, kiang, and Somali wild ass. Offspring number reflects the absolute number of offspring sired (for males) or born (for females) throughout the entire lifespan, and birth rate the number of offspring sired or born divided by the respective individual's longevity. For each factor, a separate model was constructed owing to strong correlations among traits. Data were tested for normality and transformed if necessary. The respective reproductive parameter was included as fixed covariate, and individual ID, keeping, and density as random variables. Parameters not shown in the table have been removed during model construction due to redundancy. Only P-values < 0.001 are significant after applying a sequential Bonferroni correction. Effects Estimate [+ or -] 1 SE Kulan Intercept 5633.0 [+ or -] 546.0 Males Offspring number 95.5 [+ or -] 20.1 n = 157 ID (random) 2.7 [+ or -] 4.0 Keeping 71.2 [+ or -] 126.5 Density 621.9 [+ or -] 1196.9 Kulan Intercept 6550.7 [+ or -] 520.9 Males Birth rate (lifespan) -224.5 [+ or -] 309.4 n = 157 ID (random) 4.1 [+ or -] 6.0 Keeping 5.8 [+ or -] 38.6 Density 945.7 [+ or -] 1803.3 Kulan Intercept 6943.7 [+ or -] 525.6 Females Offspring number 175.0 [+ or -] 43.3 n = 214 ID (random) 2.6 [+ or -] 4.1 Keeping 206.6 [+ or -] 435.5 Kulan Intercept 7734.8 [+ or -] 450.6 Females Birth rate (lifespan) -2897.9 [+ or -] 1018.7 n = 213 ID (random) 5.7 [+ or -] 8.5 Keeping 395.3 [+ or -] 704.9 Onager Intercept 6186.4 [+ or -] 722.1 Males Offspring number 129.6 [+ or -] 30.3 n = 96 ID (random) 13.0 [+ or -] 19.5 Keeping 7999.0 [+ or -] 11947.9 Density 30419.2 [+ or -] 50482.8 Onager Intercept 8055.9 [+ or -] 782.3 Males Birth rate (lifespan) -471.1 [+ or -] 579.0 n = 93 ID (random) 21.2 [+ or -] 31.4 Keeping 10865.0 [+ or -] 16248.8 Density 13104.5 [+ or -] 29998.0 Onager Intercept 5451.5 [+ or -] 488.9 Females Offspring number 383.3 [+ or -] 63.1 n = 144 ID (random) 10.8 [+ or -] 16.5 Onager Intercept 9081.5 [+ or -] 538.3 Females Birth rate (lifespan) -3026.9 [+ or -] 1314.0 n = 145 ID (random) 41.2 [+ or -] 59.4 Keeping 412.4 [+ or -] 836.1 Kiang Intercept 9329.3 [+ or -] 856.7 Males Offspring number 79.5 [+ or -] 47.7 n = 22 ID (random) 499.8 [+ or -] 782.3 Density 27088.5 [+ or -] 40958.4 Kiang Intercept 9747.8 [+ or -] 846.5 Males Birth rate (lifespan) 943.0 [+ or -] 1043.4 n = 22 ID (random) 632.5 [+ or -] 969.6 Density 28112.4 [+ or -] 42721.0 Kiang Intercept 7057.8 [+ or -] 1078.1 Females Offspring number 227.9 [+ or -] 161.1 n = 21 ID (random) 472.4 [+ or -] 723.7 Kiang Intercept 10387.2 [+ or -] 1170.2 Females Birth rate (lifespan) -5524.2 [+ or -] 3561.8 n = 20 ID (random) 1633.1 [+ or -] 2455.1 Somali wild ass Intercept 13864.6 [+ or -] 2130.5 Males Offspring number 91.1 [+ or -] 24.2 n = 23 ID (random) 449.0 [+ or -] 734.8 Density 55232.7 [+ or -] 95744.7 Somali wild ass Intercept 15911.7 [+ or -] 2443.4 Males Birth rate (lifespan) 1502.6 [+ or -] 691.2 n = 23 ID (random) 738.6 [+ or -] 1146.4 Density 50406.0 [+ or -] 94400.9 Somali wild ass Intercept 5086.7 [+ or -] 1195.2 Females Offspring number 689.1 [+ or -] 99.1 n = 32 Keeping (random) 2328.4 [+ or -] 7277.6 Density 84183.3 [+ or -] 184242.3 Somali wild ass Intercept 10014.9 [+ or -] 2551.4 Females Birth rate (lifespan) 2555.2 [+ or -] 3770.8 n = 32 ID (random) 384.0 [+ or -] 692.7 df F Wald Z P Kulan 1,38 106.5 < 0.0001 Males 1,155 22.6 < 0.0001 n = 157 0.7 0.4997 0.6 0.5734 0.5 0.6034 Kulan 1,8 158.2 < 0.0001 Males 1,133 0.2 0.4694 n = 157 0.7 0.4949 0.1 0.8814 0.5 0.6000 Kulan 1,79 174.5 < 0.0001 Females 1,200 16.3 0.0001 n = 214 0.6 0.5202 0.5 0.6352 Kulan 1,205 294.1 < 0.0001 Females 1,211 8.1 0.0049 n = 213 0.7 0.5037 0.6 0.5904 Onager 1,96 73.4 < 0.0001 Males 1,94 18.3 < 0.0001 n = 96 0.7 0.5050 0.7 0.5032 0.6 0.5468 Onager 1,81 10.3 < 0.0001 Males 1,89 -0.8 0.4181 n = 93 0.7 0.4982 0.7 0.5037 0.4 0.6622 Onager 1,109 124.3 < 0.0001 Females 1,142 63.1 < 0.0001 n = 144 0.7 0.5134 Onager 1,113 284.6 < 0.0001 Females 1,142 5.3 0.0227 n = 145 0.7 0.4881 0.5 0.6218 Kiang 1,22 118.6 < 0.0001 Males 1,20 47.7 0.1110 n = 22 0.6 0.5229 0.7 0.5084 Kiang 1,21 132.6 < 0.0001 Males 1,20 0.8 0.3768 n = 22 0.7 0.5142 0.7 0.5105 Kiang 1,21 42.9 < 0.0001 Females 1,21 2.0 0.1719 n = 21 0.7 0.5139 Kiang 1,20 78.8 < 0.0001 Females 1,19 3.4 0.1372 n = 20 0.7 0.5059 Somali wild ass 1,7 42.4 < 0.0001 Males 1,21 14.1 < 0.0001 n = 23 0.6 0.5412 0.6 0.5640 Somali wild ass 1,15 42.4 < 0.0001 Males 1,20 4.7 0.0416 n = 23 0.6 0.5194 0.5 0.5934 Somali wild ass 1,14 18.1 0.0009 Females 1,31 48.4 < 0.0001 n = 32 0.3 0.7490 0.5 0.6477 Somali wild ass 1,19 15.4 0.0009 Females 1,30 0.5 0.5031 n = 32 0.6 0.5794 Table 4. Reproductive parameters and the length of the reproductive phase and the post-reproductive phase. Effects of various reproductive parameters (cf. Table 1) on the length of the reproductive phase and the post-reproductive phase, respectively, using linear mixed models for kulan, onager, kiang, and Somali wild ass females. For each factor, a separate model was constructed owing to strong correlations among traits. Data were tested for normality and transformed if necessary. The respective reproductive parameter was included as fixed covariate, and individual ID, keeping, and density as random variables. Parameters not shown in the table have been removed during model construction due to redundancy. Only P-values < 0.0005 are significant after applying a sequential Bonferroni correction. Repro-ductive Effects phase Kulan Intercept Female Female longevity n = 212 ID (random) Density n = 212 Intercept Post-reproductive phase ID (random) Keeping Density n = 212 Intercept Offspring number ID (random) n = 211 Intercept Birth rate (lifespan) ID (random) Keeping n = 163 Intercept Birth rate (reproductive phase) ID (random) Density n = 212 Intercept Percentage offspring surviving > 100 days ID (random) Keeping Density n = 212 Intercept Age at first reproduction ID (random) Keeping Density Onager Intercept Female Female longevity n = 140 ID (random) n = 140 Intercept Post-reproductive phase ID (random) Keeping n = 138 Intercept Offspring number ID (random) n = 137 Intercept Birth rate (lifespan) ID (random) Keeping n = 138 Intercept Birth rate (reproductive phase) ID (random) Keeping n = 212 Intercept Percentage offspring surviving > 100 days ID (random) Keeping Density n = 139 Intercept Age at first reproduction ID (random) Keeping Kiang Intercept Female Female longevity n = 21 Intercept n = 21 Post-reproductive phase ID (random) Density n = 21 Intercept Offspring number n = 20 Intercept Birth rate (lifespan) Density (random) n = 19 Intercept Birth rate (reproductive phase) n = 20 Intercept Percentage offspring surviving > 100 days Density (random) n = 21 Intercept Age at first reproduction ID (random) Somali wild ass Intercept Female Female longevity n = 31 Intercept n = 31 Post-reproductive phase n = 31 Intercept Offspring number n = 29 Intercept Birth rate (lifespan) n = 24 Intercept Birth rate (reproductive phase) ID (random) Keeping Density n = 31 Intercept Percentage offspring surviving > 100 days ID (random) Density n = 31 Intercept Age at first reproduction Postrepro-ductive phase Effects Kulan Intercept Female Female longevity n = 215 ID (random) Density n = 230 Intercept Number of offspring Density (random) n = 213 Intercept Birth rate (lifespan) Density (random) n = 163 Intercept Birth rate (reproductive phase) Density (random) n = 230 Intercept Percentage offspring surviving > 100 days Density (random) n = 214 Intercept Age at first reproduction Density (random) Onager Intercept Female Female longevity n = 147 ID (random) n = 147 Intercept Number of offspring n = 145 Intercept Birth rate (lifespan) ID (random) n = 162 Intercept Birth rate (reproductive phase) Density (random) n = 147 Intercept Percentage offspring surviving > 100 days n = 141 Intercept Age at first reproduction Kiang Female Intercept n = 22 Female longevity n = 21 Intercept Number of offspring n = 20 Intercept Birth rate (lifespan) ID (random) n = 19 Intercept Birth rate (reproductive phase) n = 20 Intercept Percentage offspring surviving > 100 days ID (random) n = 21 Intercept Age at first reproduction ID (random) Somali wild ass Intercept Female Female longevity n = 32 Intercept n = 32 Number of offspring n = 32 Intercept Birth rate (lifespan) Keeping (random) n = 24 Intercept Birth rate (reproductive phase) n = 32 Intercept Percentage offspring surviving > 100 days Density (random) n = 31 Intercept Age at first reproduction ID (random) Repro-ductive Estimate [+ or -] 1 SE df F phase Kulan -66.6 [+ or -] 370.4 1,202 < 0.1 Female 0.4 [+ or -] < 0.1 1,212 89.9 n = 212 1.3 [+ or -] 2.0 1881.2 [+ or -] 2763.1 n = 212 3232.8 [+ or -] 284.7 1,160 128.9 -0.2 [+ or -] 0.1 1,210 8.1 4.3 [+ or -] 6.3 112.6 [+ or -] 248.2 1100.9 [+ or -] 1702.0 n = 212 1478.3 [+ or -] 242.3 1,133 37.2 291.9 [+ or -] 27.3 1,212 114.7 0.7 [+ or -] 1.1 n = 211 1167.6 [+ or -] 314.0 1,138 13.8 6016.3 [+ or -] 722.6 1,209 69.3 1.3 [+ or -] 2.1 56.0 [+ or -] 157.1 n = 163 5252.4 [+ or -] 232.6 1,161 509.8 -2667.1 [+ or -] 226.5 1,160 138.6 3515.3 [+ or -] 225.5 -209.3 [+ or -] 58.7 n = 212 4329.6 [+ or -] 566.4 1,206 58.4 -1791.6 [+ or -] 613.0 1,208 8.5 3.8 [+ or -] 5.7 78.3 [+ or -] 199.6 1803.6 [+ or -] 2690.9 n = 212 3668.8 [+ or -] 356.6 1,199 105.8 -0.4 [+ or -] 0.1 1,210 10.6 3.6 [+ or -] 5.4 128.2 [+ or -] 269.6 927.5 [+ or -] 1459.1 Onager 1684.0 [+ or -] 456.4 1,84 13.6 Female 0.5 [+ or -] 0.1 1,133 107.6 n = 140 3.5 [+ or -] 5.6 n = 140 6646.1 [+ or -] 355.3 1,45 349.8 -0.2 [+ or -] 0.1 1,138 8.2 28.8 [+ or -] 41.5 251.1 [+ or -] 541.1 n = 138 2781.2 [+ or -] 332.6 1,47 69.9 506.0 [+ or -] 43.5 1,121 135.2 2.3 [+ or -] 4.0 n = 137 5104.0 [+ or -] 464.7 1,83 120.6 3710.9 [+ or -] 1123.6 1,136 10.9 21.8 [+ or -] 31.7 197.2 [+ or -] 462.0 n = 138 6480.5 [+ or -] 537.0 1,103 145.6 -534.6 [+ or -] 1078.1 1,137 0.2 28.4 [+ or -] 41.1 293.1 [+ or -] 610.6 n = 212 4329.6 [+ or -] 566.4 1,206 58.4 -1791.6 [+ or -] 613.0 1,208 8.5 3.8 [+ or -] 5.7 78.3 [+ or -] 199.6 1803.6 [+ or -] 2690.9 n = 139 6576.7 [+ or -] 421.7 1,83 243.2 -0.2 [+ or -] 0.1 1,137 2.5 26.7 [+ or -] 38.6 159.9 [+ or -] 424.4 Kiang -557.9 [+ or -] 729.1 1,21 0.6 Female 0.6 [+ or -] 0.1 1,21 41.8 n = 21 5371.9 [+ or -] 785.7 1,6 46.7 n = 21 < 0.1 [+ or -] 0.3 1,18 < 0.1 225.3 [+ or -] 359.0 6661.0 [+ or -] 20379.1 n = 21 1467.5 [+ or -] 668.8 1,21 4.8 483.5 [+ or -] 118.2 1,21 16.7 n = 20 5421.9 [+ or -] 1242.9 1,20 19.0 1879.5 [+ or -] 3203.8 1,19 0.3 36798.7 [+ or -] 60164.6 n = 19 5732.0 [+ or -] 424.5 1,19 182.3 -2587.0 [+ or -] 641.7 1,19 16.3 n = 20 3741.2 [+ or -] 1118.1 1,19 11.2 3956.3 [+ or -] 1522.5 1,19 6.8 78183.1 [+ or -] 116382.9 n = 21 8572.8 [+ or -] 944.6 1,20 82.4 -1.8 [+ or -] 0.4 1,20 18.3 497.0 [+ or -] 723.6 Somali wild ass -420.9 [+ or -] 601.1 1,31 0.5 Female 0.5 [+ or -] 0.1 1,31 34.8 n = 31 2575.7 [+ or -] 505.7 1,31 25.9 n = 31 0.1 [+ or -] 0.2 1,31 0.1 n = 31 -215.3 [+ or -] 319.1 1,31 0.5 564.9 [+ or -] 50.2 1,31 126.5 n = 29 -291.6 [+ or -] 344.0 1,29 0.7 21532831.8 [+ or -] 2028108.4 1,29 112.7 n = 24 6979.2 [+ or -] 1751.2 1,20 15.9 -2388.1 [+ or -] 558.7 1,16 18.3 188.4 [+ or -] 408.3 189.8 [+ or -] 6478.3 69082.0 [+ or -] 143337.9 n = 31 5329.9 [+ or -] 2286.2 1,6 5.4 -473.4 [+ or -] 1478.2 1,28 0.1 125.7 [+ or -] 300.5 12566.7 [+ or -] 62398.5 n = 31 3632.2 [+ or -] 951.3 1,31 14.6 -0.5 [+ or -] 0.5 1,31 1.2 Postrepro-ductive phase Estimate [+ or -] 1 SE df F Kulan -1175.1 [+ or -] 329.5 1,126 12.7 Female 0.5 [+ or -] < 0.1 1,212 136.3 n = 215 0.3 [+ or -] 0.6 522.1 [+ or -] 821.2 n = 230 2163.7 [+ or -] 187.7 1,208 132.9 -64.5 [+ or -] 30.2 1,216 4.6 373.1 [+ or -] 664.9 n = 213 3817.8 [+ or -] 286.5 1,136 177.6 -6065.1 [+ or -] 683.3 1,213 78.8 0.6 [+ or -] 1.0 n = 163 1714.1 [+ or -] 156.7 1,78 119.7 -26.1 [+ or -] 54.6 1,163 0.2 319.9 [+ or -] 569.8 n = 230 1258.5 [+ or -] 494.7 1,229 6.5 822.6 [+ or -] 555.6 1,229 2.2 804.0 [+ or -] 1259.5 n = 214 1834.9 [+ or -] 326.2 1,180 0.1 [+ or -] 0.1 1,214 717.7 [+ or -] 1152.6 Onager -1733.0 [+ or -] 460.2 1,85 14.2 Female 0.5 [+ or -] 0.1 1,137 74.5 n = 147 3.4 [+ or -] 5.4 n = 147 1793.3 [+ or -] 241.7 1,147 55.0 -56.2 [+ or -] 49.5 1,147 1.3 n = 145 3726.9 [+ or -] 353.5 1,90 111.1 -6599.1 [+ or -] 945.5 1,145 48.7 2.6 [+ or -] 4.3 n = 162 1608.4 [+ or -] 266.6 1,155 36.4 109.1 [+ or -] 277.0 1,161 0.2 332.6 [+ or -] 588.2 n = 147 1464.1 [+ or -] 351.9 1,147 17.3 141.7 [+ or -] 441.7 1,147 0.1 n = 141 1438.8 [+ or -] 301.0 1,141 22.8 0.1 [+ or -] 0.1 1,141 0.2 Kiang Female -1198.2 [+ or -] 558.8 1,22 4.6 n = 22 0.3 [+ or -] 0.1 1,22 21.0 n = 21 572.5 [+ or -] 586.9 1,21 1.0 133.7 [+ or -] 103.8 1,21 1.7 n = 20 3619.5 [+ or -] 792.5 1,20 20.9 -5817.8 [+ or -] 2422.7 1,19 5.8 466.5 [+ or -] 728.2 n = 19 2312.0 [+ or -] 543.6 1,19 18.1 -622.1 [+ or -] 692.5 1,18 0.8 n = 20 2020.1 [+ or -] 1105.5 1,19 18.7 -359.3 [+ or -] 1490.5 1,20 19.9 150.6 [+ or -] 309.4 n = 21 2230.1 [+ or -] 971.5 1,21 5.3 -0.3 [+ or -] 0.4 1,21 0.3 60.5 [+ or -] 109.6 Somali wild ass -1081.9 [+ or -] 498.2 1,32 4.7 Female 0.4 [+ or -] 0.1 1,32 27.8 n = 32 635.9 [+ or -] 548.9 1,32 1.3 n = 32 110.7 [+ or -] 86.6 1,32 1.6 n = 32 3230.6 [+ or -] 853.3 1,31 14.3 -4373.2 [+ or -] 2183.5 1,31 4.0 5092.0 [+ or -] 9385.1 n = 24 -0.3 [+ or -] 681.0 1,24 < 0.1 1793.7 [+ or -] 678.3 1,24 7.0 n = 32 2320.8 [+ or -] 1623.1 1,11 2.0 1441.0 [+ or -] 1115.0 1,30 1.7 78.3 [+ or -] 170.7 n = 31 3813.2 [+ or -] 1500.2 1,19 6.5 0.5 [+ or -] 0.4 1,30 1.8 179.0 [+ or -] 317.4 Repro-ductive Wald Z P phase Kulan 0.8575 Female < 0.0001 n = 212 0.7 0.5063 0.7 0.4960 n = 212 < 0.0001 0.0049 0.7 0.4960 0.5 0.6501 0.6 0.5177 n = 212 < 0.0001 < 0.0001 0.6 0.5231 n = 211 0.0003 < 0.0001 0.6 0.5259 0.4 0.7215 n = 163 < 0.0001 < 0.0001 0.7 0.5012 0.7 0.5064 n = 212 < 0.0001 0.0039 0.7 0.4985 0.4 0.6948 0.7 0.5027 n = 212 < 0.0001 0.0013 0.7 0.4986 0.5 0.6345 0.6 0.5250 Onager 0.0004 Female < 0.0001 n = 140 0.6 0.5345 n = 140 < 0.0001 0.0048 0.7 0.4883 0.5 0.6426 n = 138 < 0.0001 < 0.0001 0.6 0.5545 n = 137 < 0.0001 0.0012 0.7 0.4914 0.4 0.6695 n = 138 < 0.0001 0.6208 0.7 0.4893 0.5 0.6312 n = 212 < 0.0001 0.0039 0.7 0.4985 0.4 0.6948 0.7 0.5027 n = 139 < 0.0001 0.1197 0.7 0.4898 0.4 0.7064 Kiang 0.4526 Female < 0.0001 n = 21 0.0005 n = 21 0.8990 0.6 0.5303 0.3 0.7438 n = 21 0.0396 0.0005 n = 20 0.0022 0.5642 0.6 0.5408 n = 19 < 0.0001 0.0007 n = 20 0.0034 0.0176 0.7 0.5017 n = 21 < 0.0001 0.0004 0.7 0.4922 Somali wild ass 0.4890 Female < 0.0001 n = 31 < 0.0001 n = 31 0.7037 n = 31 0.5048 < 0.0001 n = 29 0.4036 < 0.0001 n = 24 0.0007 0.0006 0.5 0.6445 < 0.1 0.9766 0.5 0.6298 n = 31 0.0003 0.7511 0.4 0.6757 0.2 0.8404 n = 31 0.0006 0.2752 Postrepro-ductive phase P Kulan 0.0005 Female < 0.0001 n = 215 0.6 0.5603 0.6 0.5250 n = 230 < 0.0001 0.0337 0.6 0.5748 n = 213 < 0.0001 < 0.0001 0.6 0.5316 n = 163 < 0.0001 0.6326 0.6 0.5745 n = 230 < 0.0001 0.1401 0.6 0.5232 n = 214 < 0.0001 0.5264 0.6 0.5335 Onager < 0.0001 Female < 0.0001 n = 147 0.6 0.5355 n = 147 < 0.0001 0.2586 n = 145 < 0.0001 < 0.0001 0.6 0.5440 n = 162 < 0.0001 0.6944 0.6 0.5718 n = 147 0.0001 0.7488 n = 141 < 0.0001 0.6943 Kiang Female 0.0433 n = 22 0.0001 n = 21 0.3405 0.2117 n = 20 0.0004 0.0265 0.6 0.5218 n = 19 < 0.0001 0.3811 n = 20 0.0836 0.8120 0.5 0.6264 n = 21 0.0321 0.4856 0.6 0.5808 Somali wild ass 0.0374 Female < 0.0001 n = 32 0.2553 n = 32 0.2099 n = 32 0.0006 0.0540 0.5 0.5874 n = 24 0.9997 0.0142 n = 32 0.1805 0.2061 0.5 0.6463 n = 31 0.0198 0.1909 0.6 0.5728 Table 5. Effects of age at each reproductive event and the sex of the previous offspring on birth interval using linear mixed models. Birth interval was included as fixed covariate, age at first reproduction as covariate, sex of the previous offspring as fixed factor, animal ID as repeated, keeping and density as random variables. Data were tested for normality and transformed if necessary. Parameters not shown in the table have been removed during model construction due to redundancy. Only P-values < 0.007 are significant after applying a sequential Bonferroni correction. Effects Estimate [+ or -] 1 SE Kulan Intercept 512.87 [+ or -] 69.33 n = 997 Age at reproduction 0.08 [+ or -] 0.01 Sex previous offspring 67.26 [+ or -] 30.43 ID (repeated) 230242.82 [+ or -] 10306.87 Keeping (random) 5.19 [+ or -] 8.22 Density (random) 6.20 [+ or -] 12.00 Onager Intercept 419.21 [+ or -] 65.91 n = 564 Age at reproduction 0.10 [+ or -] 0.02 Sex previous offspring 22.83 [+ or -] 49.48 ID (repeated) 344962.42 [+ or -] 20542.21 Kiang Intercept 218.41 [+ or -] 87.19 n = 252 Age at reproduction 0.13 [+ or -] 0.02 Sex previous offspring 26.92 [+ or -] 63.00 ID (repeated) 247931.38 [+ or -] 22087.48 Somali wild ass Intercept 355.51 [+ or -] 60.07 n = 312 Age at reproduction 0.09 [+ or -] 0.01 Sex previous offspring 5.84 [+ or -] 46.44 ID (repeated) 166274.33 [+ or -] 13312.60 df F Wald Z P Kulan 1,160 54.7 < 0.0001 n = 997 1,996 74.5 < 0.0001 1,995 4.9 0.0273 22.3 < 0.0001 0.6 0.5279 0.5 0.6047 Onager 1,564 40.5 < 0.0001 n = 564 1,564 44.0 < 0.0001 1,564 0.2 0.6447 16.8 < 0.0001 Kiang 1,252 6.3 0.0129 n = 252 1,252 41.9 < 0.0001 1,252 0.2 0.6695 11.2 < 0.0001 Somali wild ass 1,312 35.0 < 0.0001 n = 312 1,312 33.1 < 0.0001 1,312 < 0.1 0.9000 12.5 < 0.0001

Printer friendly Cite/link Email Feedback | |

Author: | Ibler, Benjamin; Fischer, Klaus |
---|---|

Publication: | Folia Zoologica |

Article Type: | Report |

Date: | Aug 1, 2017 |

Words: | 8450 |

Previous Article: | Sexual segregation in the Darwin's wild sheep, Ovis ammon darwini, (Bovidae, Artiodactyla), in the Mengluoke mountains of Xinjiang, China. |

Next Article: | Diet of adult and juvenile wildcats in Southern Tuscany (Central Italy). |

Topics: |