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:

• othus https://www.inaturalist.org/observations/90799581 and https://www.inaturalist.org/observations/7704089, vs
• americanus https://www.inaturalist.org/observations/47575739 and https://www.inaturalist.org/observations/117552519 and https://www.inaturalist.org/observations/105010624.

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 two largest-bodied species (4.5 kg or more), namely othus and arcticus, tend to have conspicuous colouration, and
• species with body mass 2 kg or less tend to have inconspicuous colouration, to the exclusion of even auricular and caudal flags (https://www.inaturalist.org/journal/milewski/63961-interspecific-variation-in-flags-as-features-of-adaptive-colouration-in-hares-part-1-lepus-californicus#), but
• gregariousness/pair-bonding seems as important as body size in explaining the conspicuous colouration in othus, arcticus, timidus, europaeus, and callotis.

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.

Publicado el mayo 24, 2022 10:27 TARDE por milewski