Patterns of body size in hares

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The genus Lepus (https://en.wikipedia.org/wiki/Hare) contains about 32 species. These vary in average body mass by nearly five-fold, from about 1 kg in the smallest species to about 5 kg in the largest species.

Furthermore, this variation in body size does not generally conform to Bergmann's rule (https://en.wikipedia.org/wiki/Bergmann%27s_rule and https://www.tau.ac.il/lifesci/zoology/members/yom-tov/articles/Geographic_variation.pdf).

In this Post, I

  • list all the species of Lepus in decreasing order of body mass,
  • point out the biggest anomalies relative to Bergmann's rule,
  • seek general correlations between adaptive colouration and body size, and
  • suggest that stotting is restricted to large-bodied species plus a medium-size species characterised by pair-bonds.

The following list of the species of Lepus, in descending order of average adult body mass, is based mainly on Chapman and Flux (1990, https://portals.iucn.org/library/node/6047).

othus 4.8 kg
arcticus 4.5 kg
europaeus 3.8 kg
alleni 3.6 kg
saxatilis 3.5 kg
tibetanus (https://en.wikipedia.org/wiki/Desert_hare)/tolai (https://en.wikipedia.org/wiki/Tolai_hare) 3.5 kg
townsendii 3.25 kg
timidus 3 kg
flavigularis ?3 kg
castroviejoi 2.9 kg (https://animaldiversity.org/accounts/Lepus_castroviejoi/)
starckii 2.75 kg
callotis 2.7 kg
granatensis ?2.5 kg (https://animaldiversity.org/accounts/Lepus_granatensis/)
insularis 2.5 kg
oiostolus 2.5 kg
nigricollis 2.5 kg
brachyurus 2.5 kg
californicus 2.5 kg
capensis most subspecies ?2 kg
peguensis 2.25 kg
victoriae 2 kg
habessinicus 2 kg
comus 2 kg
fagani ?2 kg
melainus 1.84 kg
mandshuricus 1.8 kg
coreanus ?1.8 kg
sinensis 1.6 kg
hainanus 1.5 kg
yarkandensis 1.4 kg
americanus 1.3 kg
capensis subspecies omanensis and cheesmani 1 kg

The main support for Bergmann's rule lies in the fact that the largest-bodied species, namely Lepus othus, is restricted to Alaska (https://upload.wikimedia.org/wikipedia/commons/4/49/Lepus_othus_range_in_ak.png). However, this is undermined by the fact that also occurring in Alaska is the smallest-bodied species, namely Lepus americanus (https://en.wikipedia.org/wiki/Snowshoe_hare#/media/File:Lepus_americanus_map.svg).

The following photos, all taken in Alaska, show that the above two species look similar without any scale to show the nearly five-fold difference in body mass:

Furthermore, a single species, namely L. capensis, varies greatly among its subspecies within a limited range of latitudes in the Middle East (https://www.inaturalist.org/journal/milewski/42001-the-mystery-of-the-arabian-miniatures#). This is nicely illustrated by Figure 302, on page 213 of Harrison and Bates (1991).

The very smallest-bodied form of Lepus, namely L. capensis jefferyi, occurs on a coastal island in Arabia, namely Masirah Island (https://en.wikipedia.org/wiki/Masirah_Island). However, this does not detract from the fact that the subspecies of the nearby mainland in the mountains of Oman, namely L. capensis omanensis, is nearly as small-bodied. Furthermore, the subspecies of the vast sandy deserts (http://saudi-archaeology.com/background/geography-arabian-peninsula/) of the Rub al Khali (https://en.wikipedia.org/wiki/Rub%27_al_Khali), Dahana (https://www.britannica.com/place/Al-Dahna), and Nafud (https://www.britannica.com/place/al-Nafud), namely L. c. cheesemani, is also surprisingly diminutive despite occurring at medium latitudes straddling the Tropic of Cancer.

Defying any simple pattern, the smallest-bodied species and subspecies of Lepus fall into disparate ecological categories, namely

  • species adapted to forests (americanus in the subarctic and hainanus in the tropics), vs
  • species adapted to deserts (yarkandensis in northwestern China and certain subspecies of capensis in Arabia).

The general relationship between body size and adaptive colouration is as follows:

The relationship between body size and ostensible stotting in Lepus, although poorly-documented (see https://www.inaturalist.org/journal/milewski/66356-do-hares-ever-stot#), is as follows:

  • in large-bodied species (more than 3.5 kg), stotting tends to be bipedal,
  • quadrupedal stotting seems to occur only in several species (e.g. europaeus, townsendii, callotis) of body mass 2.7 kg or more, the smallest-bodied species of which (callotis) being unusual in its pair-bonded social structure, and
  • stotting of any kind has yet to be seen in any species of body mass less than 2.7 kg.
Posted by milewski milewski, May 24, 2022 22:27

Comments

Fascinating! Thank you! I have enjoyed learning so much from you, and with amazement. Ruth

Posted by grinnin 3 months ago (Flag)

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