Archivos de diario de enero 2023

03 de enero de 2023

Kangaroos breed slowly compared to ruminants

"How rapidly do kangaroos breed" is an important question, if we are to understand the nature of Australia.

This continent has lacked any terrestrial wild predator larger than a dog (https://en.wikipedia.org/wiki/Dingo), for thousands of years.

Carnivores depend on the productivity of their prey. Why did no carnivore specialise on kangaroos, in the way the cheetah (Acinonyx jubatus, https://www.inaturalist.org/taxa/41955-Acinonyx-jubatus) specialises on gazelles in Africa and Asia?

The answer lies partly in an understanding of the reproductive system of kangaroos.

It is true that an individual female can have three dependent offspring, in various stages of growth at the same moment. However, this is evidence of slow, rather than fast, growth. An overlap of this kind may amount to an insurance policy, allowing at least one offspring to survive under conditions that are generally unfavourable for growth.

How to compare reproductive rates?

Kangaroos can be compared with the most similar herbivores under similar climates on other continents. Body size is a prime factor. Reproduction is likely to be more rapid in small-bodied than in large-bodied species, and the corollary is that lifespan is shorter in the former than in the latter.

Adult female kangaroos have body masses of 25-35 kg. Terrestrial herbivores of similar body size, under similar climates, consist of various ruminants and one large rodent. Since males of kangaroos eventually grow to double the body mass of females in middle age (older than 10 years), other herbivores of up to 65 kg can also be considered comparable.

Reproductive rates can be measured as either the rate of increase of populations free of predators, or the rate at which an established population can be culled with no risk of extermination. The prime factors are how fast females grow to breeding age, and how many offspring they pack into a single litter. Periods need to be calculated from conception , not from birth, because pregnancy in kangaroos is extremely brief.

Populations of the red kangaroo (Macropus rufus, https://www.inaturalist.org/taxa/42885-Macropus-rufus and https://australian.museum/learn/animals/mammals/red-kangaroo/) can be culled at an average of up to 15% per year. An annual offtake rate of 3 out of every 20 in the population seems to be sustainable in the long term.

The corresponding figures for grey kangaroos (Macropus fuliginosus https://www.inaturalist.org/taxa/42881-Macropus-fuliginosus and Macropus giganteus https://www.inaturalist.org/taxa/42888-Macropus-giganteus) and the common wallaroo (Macropus robustus, https://www.inaturalist.org/taxa/42872-Macropus-robustus) seem to be 13% and 11%, respectively. These rates of reproduction are modest for mammals of this body size.

No match for ruminants:

Kangaroos are often compared to ruminants. However, the many spp. of ruminants maintain rapid reproduction and growth over a wide range of body sizes.

Species the size of kangaroos generally outbreed kangaroos two-to-one. Only the largest-bodied of ruminants, or those living on mountaintops or in the Arctic, reproduce as slowly as kangaroos do.

The domestic sheep (Ovis aries, https://www.inaturalist.org/taxa/121578-Ovis-aries) is very variable, according to breed and plane of nutrition. Sustainable offtake in sheep varies from 15% in the case of the merino breed that coexists with kangaroos, to 300% in the case of the most prolific breeds on other continents.

In the domestic sheep, growth from conception to sexual maturity takes at least 5 months, and usually 15 months, which is less than in the red kangaroo. Females of the domestic sheep - despite being the more massive - have a shorter lifespan than that of females of kangaroos.

Wool breeds allocate protein to fleece instead of milk, and females wean only one offspring each per year. Nevertheless, the merino breed (https://en.wikipedia.org/wiki/Merino) in Australia outbreeds the red kangaroo, relative to body mass.

Average reproductive rates are similar, but females of the ungulate (65 kg) grow to double the body mass of females of kangaroos. Therefore, even wool-producing breeds of sheep can produce food for meat-eaters more rapidly than can any of the four spp. of kangaroos mentioned so far.

Please note the following:

Kangaroos are renowned for nurturing up to 3 offspring simultaneously. However, the finnsheep does the same for up to 10 offspring (5 in the womb, 5 at the udder).

Thus, the most prolific breeds of sheep reproduce up to 20-fold more rapidly than kangaroos do, if comparisons are made on a long-term basis with correction for differences in body mass of females.

The domestic goat (Capra hircus, https://www.inaturalist.org/taxa/123070-Capra-hircus) reproduces several-fold more rapidly than the coexisting common wallaroo does. The feral goat normally bears twins in semi-arid Australia, whereas the common wallaroo has the slowest reproduction among kangaroos.

Relatives of camels breed as slowly as kangaroos:

The largest ruminants, giraffes (Giraffa spp., https://www.inaturalist.org/taxa/42157-Giraffa-camelopardalis), sustain an average offtake of 15% of the population per year, on cattle ranches in Africa where they are conserved and culled. Like kangaroos, giraffes bear a single newborn. This means that kangaroos breed no more rapidly than a ruminant 25-fold their body mass (females: 30 kg vs 800 kg; males: 65 kg vs 1300 kg).

Other large ruminants err to one side or the other of the value of 15%. For example, Bison bison (https://www.inaturalist.org/taxa/42408-Bison-bison) has one offspring per birth, breeds in only 2 of every 3 years, and sustains an average offtake of 10%. The moose (Alces alces, https://www.inaturalist.org/taxa/522193-Alces-alces) often has twins, and sustains an average offtake of more than 20%.

Camels, unlike giraffes, deer, and other true ruminants, reproduce relatively slowly. The vicugna (Vicugna vicugna, https://www.inaturalist.org/taxa/42236-Vicugna-vicugna) is the smallest living member of the camel family, and approaches kangaroos in body mass as well as its diet of grass. Whereas the domestic sheep is pregnant for 5 months, the like-size vicugna is pregnant for 11 months. The sustainable rate of offtake for the vicugna is likely to be less than 10% per year.

The vicugna is restricted to the Andes in South America, at double the altitude of the Australian Alps (https://en.wikipedia.org/wiki/Australian_Alps). It is less prolific than kangaroos, probably because its food supply is always limited.

Prolific ruminants of arid climates:

The springbok (Antidorcas marsupialis, https://www.inaturalist.org/taxa/42283-Antidorcas-marsupialis) is a ruminant of similar body mass and diet to the red kangaroo, restricted to dry climates in southern Africa, and likewise culled on sheep pastures.

Please note the following:

  • Although the springbok bears only 1 offspring per birth, this species of gazelle can sustain double the offtake rate of the kangaroo (about 30% per year).
  • Females of the springbok usually mature sexually in less than half the time taken by females of the red kangaroo: 13 months vs 31 months after conception.
  • Under good conditions, females of the springbok can reach sexual maturity less than 1 year after being conceived, a record unmatched by any kangaroo.
  • The springbok can bear 2 offspring per year after good rainfall, because it is pregnant for less than 6 months, and the mother is prepared to mate shortly after giving birth.
  • The only gazelle commonly bearing twins is a relatively small-bodied species, Gazella subgutturosa (https://www.inaturalist.org/taxa/568727-Gazella-subgutturosa), which is able to survive the cold winters of Asia.

It is true that the red kangaroo can reproduce rapidly after rainfall, with each mother having up to 3 offspring in various stages of development: 1 freely suckling, 1 attached inside the pouch, and 1 in the womb. However, this does not compensate for the relatively slow growth of these offspring. Even in the best of seasons, the red kangaroo mother can wean no more than 3 offspring in 2 consecutive years, compared to 4 in the case of the springbok.

Herbivores in the extremely arid Sahara Desert are also prolific. Two spp. of gazelles just manage to survive in the central Sahara, after decades of persecution with sophisticated firearms and all-terrain vehicles.

Gazella leptoceros (https://en.wikipedia.org/wiki/Rhim_gazelle), similar in body mass to kangaroos, has always been restricted to sandy desert in North Africa. Remnant populations of the cheetah have been recorded in the Sahara (https://en.wikipedia.org/wiki/Northeast_African_cheetah#:~:text=Once%20existing%20in%20Egypt%2C%20the,blindfolded%2C%20and%20kept%20on%20leashes.).

The cheetah is likely to be particularly dependent on the fecundity of its prey in desert, where all herbivores are naturally rare. This felid, twice as massive as the extinct thylacine (Thylacinus cynocephalus, https://en.wikipedia.org/wiki/Thylacine) of Australia, may have survived to this day in a habitat more barren than the heart of Australia.

Giant rodents and grazing apes:

The capybara (Hydrochoerus hydrochaeris, https://www.inaturalist.org/taxa/74442-Hydrochoerus-hydrochaeris) is the largest rodent on Earth, similar in body mass to kangaroos. It is culled on cattle ranches in South America, with a sustainable offtake of about 35%. The capybara reproduces far more rapidly than kangaroos do, because it bears 1-8 (usually 2-6) offspring per litter.

The gelada (Theropithecus gelada, https://www.inaturalist.org/taxa/43530-Theropithecus-gelada) of the Ethiopian Highlands is the only living primate that relies on green grass for food, and it inhabits treeless grassland. This is the most strictly herbivorous and terrestrial of all monkeys, and is therefore comparable with kangaroos.

Primates in general breed slowly, and the gelada is no exception. It reproduces below par for kangaroos, because females take twice as long to reach sexual maturity, and give birth only once every two years. Like the vicugna, the gelada is adapted to altitudes beyond the ranges of most comparable ruminants.

Why are kangaroos not prolific?

Marsupials should be capable of rapid reproduction, because the small size of newborns potentially allows many offspring to be packed into each litter. For example, 56 maggot-size individuals emerged from one birth of the North American opossum (Didelphis virginiana, https://www.inaturalist.org/taxa/42652-Didelphis-virginiana).

This marsupial has a short natural lifespan for a mammal of its size (3 kg), dying of old age at 3 years even if it has survived predators and winter snow. Females wean 9-12 offspring in the second hear of life, and largely rely in this one summer's maternal effort for the propagation of the species. Therefore, the consistent restriction of kangaroos to 1 offspring per birth, and their extended lifespan (more than 20 years), are not merely the result of their genetic heritage as marsupials.

Drought does not seem to be the limiting factor. The original numbers of kangaroos were modest, even after a series of years with more than average rainfall.

The tropical north of Australia has copious rainfall and perennial rivers. However:

In southern Australia, the red kangaroo of the semi-arid interior outreproduces the grey kangaroos of coastal woodlands, if long-term averages are compared. However, the fecundity of the red kangaroo remains modest, even where bore water is provided.

Originally, kangaroos were remarkably scarce in the treeless mitchell grassland (dominated by Astrebla, a grass restricted to Australia) that covers an area the size of Britain (450000 square kilometres) in the northern half of Australia (https://en.wikipedia.org/wiki/Mitchell_Grass_Downs and https://www.agric.wa.gov.au/rangelands/mitchell-grass-alluvial-plain-pastures-pilbara-western-australia#:~:text=Curly%20Mitchell%20grass%20(Astrebla%20lappacea,)%20of%2010%20to%2025%25.).

Mitchell grassland is as extensive as the Highveld (https://en.wikipedia.org/wiki/Highveld) in South Africa, and is the closest equivalent in Australia to prairies and steppes on other continents. However, it lacked the expected herds of herbivores.

Research by Alan Newsome (https://www.eoas.info/biogs/P005736b.htm), together with traditional aboriginal knowledge, revealed that kangaroos were not migratory, and failed to graze mitchell grassland even after rain, before the advent of domestic livestock.

Kangaroos are adapted to nutrient-poverty:

Australia is the nutrient-poorest continent. Virtually all of its soils are poor in macronutrients (e.g. phosphorus) or micronutrients (e.g. cobalt), or unbalanced in their combinations of nutrients.

On other continents, herbivores with slow reproduction are marginalised to the most challenging environments. In Australia, they are prevalent in the form of kangaroos, owing to continent-wide nutrient-poverty, compounded by intense wildfire.

Nutrient-poverty, and a lack of succulent plants other than halophytes, explains why kangaroos have a limited ability to exploit arid environments.

All spp. of kangaroos are absent from parts of the Simpson and Great Sandy Deserts (maps by Graeme Caughley, https://www.goodreads.com/book/show/6819726-kangaroos and https://en.wikipedia.org/wiki/Graeme_Caughley and https://www.science.org.au/fellowship/fellows/biographical-memoirs/graeme-james-caughley-1937-1994). Even the spp. of the arid interior need drinking water or shade.

The red kangaroo depends mainly on alluvial woodlands, which retain a few pools evening droughts. The common wallaroo depends on boulder outcrops far from water, which provide shade even at noon.

By contrast, the springbok is extremely adapted for drought, and resides year-round in the Namib Desert, which is more arid (average less than 100 mm of rainfall per year) than the Simpson and Great Sandy Deserts. Although unlikely to reproduce in severe drought, adults of the springbok need neither drinking water nor shade to survive until the next episode of rain. The springbok seldom drinks even when water is available, although it visits pans (salinas, https://journals.co.za/doi/abs/10.10520/AJA03794369_3442) to eat succulent plants and to eat nutrient-rich earth.

Adaptation to nutrient-poverty would explain the paradox of limited reproductive rates of kangaroos, and their absence from large areas. Even the clay soils of mitchell grassland seem too poor to support the succulent plants capable of sustaining herbivores in drought. Unlike ruminants, kangaroos are unknown to eat earth as a nutritional supplement. The possible reason for this that such supplements are unavailable on the ancient, deeply weathered continent of Australia.

Whatever the reason, the contrast between semi-arid Australia and southern Africa was extreme. Although red kangaroo and springbok both prefer palatable, small grasses such as Enneapogon (a genus indigenous to both continents, https://www.inaturalist.org/observations?place_id=any&taxon_id=72116&view=species), the springbok was prolific to a degree unmatched in Australia.

Colonists of South Africa observed irruptions of tens of millions of individuals walking shoulder-to-shoulder, sweeping sheep before them, and denuding the vegetation over areas exceeding 100 km by 10 km.

Sceptical readers will realise that I have understated these 'springbok treks', on referring to eye-witness accounts (see J D Skinner and G N Louw, 1996, Transvaal Museum Monographs, no. 10, https://www.biblio.com/book/springbok-antidorcas-marsupialis-zimmermann-1780-transvaal/d/938429382). The springbok multiplied its populations rapidly, despite being prey to at least 4 spp. of carnivores larger than the dingo, and many other predators.

Irruptions were repeatedly recorded, most recently in 1896 (https://www.tandfonline.com/doi/abs/10.1080/00359199309520276?journalCode=ttrs20 and https://www.jstor.org/stable/29734323).

Publicado el enero 3, 2023 05:06 MAÑANA por milewski milewski | 11 comentarios | Deja un comentario

09 de enero de 2023

Gaudy bovids vs taily deer

Here I test the idea that, whereas bovids tend to have bold whole-body markings, cervids tend to have conspicuous erectile tails.

I have searched for the three most boldly-marked species/subspecies of first bovids, then cervids. Then I have searched for the three species/subspecies, in each family, that have tails that tend to be displayed in conspicuous form when raised.

The three most boldly-marked bovids, at a whole-body scale:

https://www.krugerpark.co.za/africa_bontebok.html

https://www.mindenpictures.com/stock-photo-sable-antelope-hippotragus-niger-in-hwange-national-park-zimbabwe-naturephotography-image90037248.html

Publicado el enero 9, 2023 07:11 MAÑANA por milewski milewski | 3 comentarios | Deja un comentario

20 de enero de 2023

The western wildebeest: a natural hybrid between the black and blue wildebeests?

I have previously shown that what I call the western wildebeest

  • should be distinguished from the blue wildebeest (Connochaetes taurinus taurinus), and
  • already has a taxonomically legitimate name, viz. Connochaetes taurinus mattosi, which for mainly historical reasons has been overlooked.

Please see https://www.inaturalist.org/journal/milewski/67992-photo-pair-summarising-the-distinction-between-blue-wildebeest-and-western-wildebeest# and https://www.inaturalist.org/journal/milewski/54306-how-one-of-the-most-familiar-of-african-large-mammals-came-to-be-unrecognised#.

It is also known that the two South African spp. of wildebeests, namely C. taurinus and the black wildebeest (Connochates gnou), are capable of producing fertile hybrids (https://link.springer.com/article/10.1007/s10592-018-1071-x and https://link.springer.com/article/10.1007/s10344-011-0567-1).

The context in which hybridisation has been discovered is the holding of both spp. together, under artificial conditions, on game ranches. However, the natural distributions did overlap even under natural conditions, in and near what is now Free State province of South Africa, at the time of European arrival (https://www.researchgate.net/figure/Overlap-of-species-distribution-of-blue-and-black-wildebeest-Map-was-redrawn-from-IUCN_fig2_265128890 and https://www.researchgate.net/figure/Historical-distribution-ranges-of-blue-light-blue-and-black-wildebeest-greyThe_fig3_322539832).

In this Post, I hypothesise that the natural origin of C. t. mattosi has been by virtue of past (Pleistocene) hybridisation between C. taurinus and C. gnou.

I base this on the observation that most of the ways in which C. t. mattosi differs from C. t. taurinus are in line with the nature of C. gnou.

These are as follows.

Brindling is well-developed in C. t. taurinus (http://www.safari-club.co.uk/photo-galleries/kenya-familiarisation-trip-2010/dsc_0062/), minimally developed in C. gnou, and intermediate in C. t. mattosi.

The mane is lax in C. t. taurinus, vs stiff in C. gnou. In C. t. mattosi, the mane is stiff, making this the only form in the taurinus-complex that possesses a stiff mane.

The beard is lax and short in C. t. taurinus (https://www.gettyimages.com.au/detail/photo/close-up-of-blue-wildebeest-greater-kruger-national-royalty-free-image/81897934?phrase=blue%20wildebeest%20south%20africa&adppopup=true), vs stiff and relatively long in C. gnou (https://www.istockphoto.com/photo/black-wildebeest-gm887262280-246261777?phrase=wildebeest%20fur%20close%20up). In C. t. mattosi, the beard is far better-developed than in C. t. taurinus, and is particularly stiff (https://www.gettyimages.com.au/detail/photo/stripe-gnu-in-the-etosha-national-park-in-namibia-royalty-free-image/1297158239?phrase=blue%20wildebeest%20south%20africa&adppopup=true).

Sheen on the rump is noticeable in C. t. taurinus (albeit not as well-developed as in mearnsi or albojubatus), vs absent in C. gnou. In C. t. mattosi, sheen on the rump is hardly noticeable.

Paleness (depigmentation) on the proximal part of the mane (i.e. at the base of the mane) is well-developed in C. gnou, vs poorly-developed in C. t. taurinus. In C. t. mattosi, this feature seems to have an intermediate occurrence.

Infants tend to be paler (apart from the feet) in C. t. taurinus (https://www.gettyimages.com.au/detail/photo/side-view-of-buffalo-grazing-on-field-bushbuckridge-royalty-free-image/1347710373?phrase=blue%20wildebeest%20south%20africa&adppopup=true and https://www.alamy.com/stock-photo-baby-blue-wildebeest-connochaetes-taurinus-with-mother-21318646.html?imageid=B9A71E5D-12A8-4A62-992C-AAE26EA50A2A&p=50730&pn=1&searchId=4093b7b4151429bdd59b4c6faf51ee5c&searchtype=0 and https://www.reddit.com/r/wildlifephotography/comments/107gvvp/blue_wildebeest_with_suckling_calf_black_rhino/ and https://www.flickr.com/photos/antonettevdb/24818598341) than in C. gnou (https://www.youtube.com/watch?v=YQ-JJyS9HSo and https://www.irishnews.com/magazine/daily/2019/08/27/news/rare-baby-wildebeest-born-at-newquay-zoo-1696156/ and https://www.zooborns.com/zooborns/2009/07/newquay-welcomes-a-leggy-wildbeest.html).

In C. t. mattosi, the tone of infants seems intermediate (https://cloudfront.safaribookings.com/library/zambia/xxl/Liuwa_Plain_National_Park_041.jpg).

I can think of two alternative hypotheses for the origin of C. t. mattosi.

Firstly, C. t. mattosi may be a paedomorphic version of C. t. taurinus (https://www.inaturalist.org/journal/milewski/54384-the-western-wildebeest-as-an-example-of-paedomorphic-evolution#). This hypothesis is not mutually exclusive with the approach taken in the present Post.

Secondly, C. t. mattosi may have arisen by natural selection, free of any hybridisation, under ecological conditions different from those to which C. t. taurinus is adapted. South of the Kunene and Okavango Rivers, this seems to make sense, because C. t. mattosi is associated with Kalahari sand and semi-arid climates. However, it is undermined by the fact that C. t. mattosi extends deep into mesic south-central Africa, in the countries of Angola and Zambia.

Publicado el enero 20, 2023 01:12 MAÑANA por milewski milewski | 2 comentarios | Deja un comentario

28 de enero de 2023

Adaptive colouration in the vicuna (Camelidae: Vicugna vicugna)

Please see https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6562099/.

The vicuna (Vicugna vicugna, https://www.shutterstock.com/image-photo/vicuna-arid-landscape-chimborazo-nature-reserve-603780842 and https://www.inaturalist.org/observations/69950772 and https://en.wikipedia.org/wiki/Vicuna and https://animaldiversity.org/accounts/Vicugna_vicugna/) has woolly pelage, adapted to the snow-free cold at high altitudes in the Andean altiplano (https://en.wikipedia.org/wiki/Altiplano).

Please see https://www.nwf.org/Magazines/National-Wildlife/2002/Return-of-the-Golden-Fleece and https://critterfacts.com/vicuna/ and http://elelur.com/mammals/vicuna.html and https://www.bioexpedition.com/vicuna/ and https://www.nationalparks-worldwide.com/sam/peru/national-parks/vicunas/vicunas.html.

Nothing seems previously to have been written about the adaptive colouration of this, the smallest of camelids (https://escholarship.org/content/qt7xs9j2zs/qt7xs9j2zs.pdf).

DIFFERENCE BETWEEN SUBSPECIES:

The vicuna has

The two differ in their patterns of colouration, as follows:

CONCEPTUAL FRAMEWORK:

The vicuna depends on short vegetation, and is diurnal and gregarious (https://www.istockphoto.com/photo/vicuna-gm529652033-54217656?phrase=vicuna%20and%20young%20in%20lauca%20national%20park).

It would, therefore, be unsurprising if - based on the trends seen in comparable deer and bovids - the pelage of the vicugna were to have conspicuous features of pigmentation/depigmentation.

And indeed, the colouration of the vicuna is such that it tends to stand out from its environment. This is by means of large-scale pale features of the pelage.

However:
What is surprising is the position of the most conspicuous feature of the colouration of the northern ssp.
This is located on the front of the figure (Vicugna vicugna mensalis: https://www.alamy.com/vicua-and-the-volcano-misti-reserva-nacional-salinas-y-aguada-blancaper-image357300976.html?imageid=79108214-DCF7-48E4-A45A-28C871E28077&p=16583&pn=1&searchId=29cecb4231d7c99f92316b37750496dd&searchtype=0).

Most comparable deer and bovids emphasise the posterior, not the anterior, of the figure. The northern ssp. of the vicuna instead combines a frontal bleeze, centred on the chest, with otherwise fairly plain colouration in both sexes.

The pattern seen in the northern ssp. of the vicuna thus differs from that in any other ungulate.

FRONTAL BLEEZE:

The frontal bleeze of the northern ssp. of the vicuna (https://www.mediastorehouse.com.au/ardea-wildlife-pets-environment/fg-aj-105-1303400.html) is an adaptively conspicuous feature, consisting of the following elements:

The frontal bleeze is conspicuous

This is true notwithstanding the fact that no part of the pelage of the vicuna is dark enough to provide particular contrast to the pale surfaces.

CALEONIC COLOURATION:

In the southern subspecies of the vicuna, the pale of the ventral surface of the torso has been extended upwards, anterior and posterior to both the shoulders/scapula and the haunch/upper hindleg.

This results in pale pelage extending broadly and diffusely on to

  • the junction of neck and torso,
  • above the elbow,
  • from groin to hips, and
  • on the buttocks.

Please compare the vicugna with a typical example of caleonic colouration, namely Equus khur:
https://stock.adobe.com/images/indian-wild-asses-equus-hemionus-khur-also-known-as-baluchi-wild-ass-in-the-raan-of-kutch-a-saline-desert-in-gujarat-the-last-natural-sanctuary-for-this-sub-species-of-wild-ass/239537503 and https://fineartamerica.com/featured/1-indian-wild-ass-equus-hemionus-khur-pete-oxford.html.

The following illustrate caleonic colouration in the southern subspecies of the vicuna:
https://www.inaturalist.org/observations/121600503 and https://www.inaturalist.org/observations/88307462 and https://www.shutterstock.com/image-photo/vicunas-salar-de-tara-desert-atacama-112162280 and https://www.inaturalist.org/observations/141842864 and https://www.inaturalist.org/observations/141842863 and https://www.inaturalist.org/observations/38702920 and https://www.inaturalist.org/observations/141842865 and https://www.shutterstock.com/image-photo/group-vicunas-99233132 and https://www.shutterstock.com/image-photo/vicuna-vicgna-vicugna-high-altitude-camelid-22334845 and https://www.shutterstock.com/image-photo/portrait-vicuna-vicugna-by-chalviri-lagoon-1999882352 and https://www.inaturalist.org/observations/47665170 and https://www.shutterstock.com/image-photo/vicuna-vicgna-vicugna-high-altitude-camelid-22503727.

Caleonic colouration in the vicuna results in both

  • the de-emphasis of the pale frontal pelage, and
  • the emphasis of the pale tract on the hips (ileum) in particular.

FACIAL FLAG:

The cheeks of the vicuna (https://www.shutterstock.com/image-photo/portrait-vicuna-vicugna-selective-focus-2145439021) are pale/sheeny enough to be noticeable in many views, This is likely to add to the conspicuousness of the figure (https://pavonivaganti.com/en/vicuna-what-it-is/ and https://www.inaturalist.org/observations/43003648), particularly when the head is moved.

The facial flag qualifies as a conspicuous feature, notwithstanding that

  • the head is remarkably small, relative to the proportions seen in comparable deer and bovids,
  • the paleness of the cheeks seems to be owing partly to a sheen effect rather than depigmentation,
  • the neck is so long that it widely separates the cheeks from the pale chest, and
  • there is no contrasting dark on the head, other than the eyes.

The following shows that, in certain illumination, the cheeks are not noticeably pale: https://andrebaertschi.photoshelter.com/image/I0000SbSgFVcjZPU.

The following is a particularly clear illustration of the hypothetical sheen-effect on the cheek in the southern ssp., V. v. vicugna: https://www.inaturalist.org/observations/61325869.

The following are comparable views, lacking the sheen-effect: https://www.inaturalist.org/observations/107312217 and https://www.inaturalist.org/observations/139067636 and https://www.inaturalist.org/observations/66795801 and https://www.inaturalist.org/observations/146260487 and https://www.inaturalist.org/observations/105434200 and https://www.inaturalist.org/observations/140082618 and https://www.inaturalist.org/observations/37686762.

The following show what is probably the true (modest) degree of depigmentation of the cheeks: https://www.inaturalist.org/observations/141842864.

The following seems to show the sheen-effect in partial effect: https://www.inaturalist.org/observations/140837038.

INCONSPICUOUS HINDQUARTERS:

No pattern on the rump/buttocks of the vicuna seems conspicuous enough to qualify as a bleeze or flag.

This holds true for both subspecies:

The relative inconspicuousness of the hindquarters holds, notwithstanding the facts that

The following show the white tail-tip in the two subspecies:

COMPARISON WITH GUANACO:

The guanaco (Lama guanicoe, https://www.inaturalist.org/taxa/42240-Lama-guanicoe) is worth comparing with the vicuna, because

The southern subspecies of the vicuna resembles the guanaco in its colouration, apart from the lack of any dark on tail or face (https://www.inaturalist.org/observations/61325069).

For the two species overall, the main differences are that

WHY DOES THE NORTHERN SUBSPECIES OF THE VICUNA ADVERTISE ITSELF FRONTALLY?

The habitat of the vicuna is relatively free from predators. This is because

  • South America as a whole has relatively few large carnivores,
  • the Andes are relatively remote and quasi-insular, and
  • within the Andes, the vicuna prefers plains offering minimal cover to predators.

This relative freedom from predation is consistent with

Bleezes and flags function as signals to both conspecifics and predators. In most deer and bovids possessing bleezes and flags, two of the functions of these features are to signal that

  • the individual/group has spotted the predator and is alert and ready to flee, and
  • the individual is fit and thus unlikely to be pursued successfully.

Given the communication with predators, it makes sense that most deer or bovids emphasise the hindquarters in their conspicuous displays.

However, in the case of the vicuna, most signalling is instead likely to be intraspecific/social, and free of implications of imminent flight.

Therefore, it may make sense that the main conspicuous feature on the figure is frontal, facilitating communication in contexts other than encounters with predators.

However, this does not explain the lack of the frontal bleeze in the southern subspecies. Do readers have better ideas?

Also see:
https://www.inaturalist.org/journal/milewski/75011-observations-in-inaturalist-remain-insufficient-to-draw-the-border-between-the-two-subspecies-of-the-vicuna#
https://www.inaturalist.org/posts/75256-subtle-and-multifaceted-adaptive-colouration-in-the-largest-wild-ruminant-in-south-america-the-guanaco-lama-guanicoe#
https://www.inaturalist.org/journal/milewski/75397-comments-on-subspeciation-in-the-wild-camelids-of-south-america#

Publicado el enero 28, 2023 10:11 MAÑANA por milewski milewski | 37 comentarios | Deja un comentario

30 de enero de 2023

Caleonic colouration in the caribou, part 1: Rangifer tarandus terranovae

Naturalists are used to thinking that animals tend to have adaptive colouration that blends into the surroundings.

However, in open environments where it is hard to hide, certain animals opt instead to have conspicuous colouration.

One well-recognised pattern of conspicuous colouration in medium-size to large animals is the pied pattern (https://www.tripadvisor.com/LocationPhotoDirectLink-g469397-d469470-i381557535-Bontebok_National_Park-Swellendam_Overberg_District_Western_Cape.html and https://www.flickr.com/photos/myplanetexperience/50867088327 and https://www.inaturalist.org/posts/67541-the-most-picturesque-of-antelopes-and-deer-in-their-most-picturesque-settings#).

This consists of a dark/pale patchwork, too bold to function disruptively. I.e. pied colouration is too conspicuous for the figure to be camouflaged.

However, there is another conspicuous pattern, less familiar but obvious in certain mammals. I provisionally call this 'caleonic', because it deserves a name, but has not previously been described.

In the caleonic pattern, it is as if the figure is 'highlit' by a flame below.

Caleonic colouration seems to have arisen repeatedly in lineages as diverse as

Animals with caleonic colouration have, in a sense, ‘stretched’ the principle of countershading (https://en.wikipedia.org/wiki/Countershading) to breaking-point. This extension of pale pelage, upwards, has achieved whole-body conspicuousness instead of crypsis (https://en.wikipedia.org/wiki/Crypsis).

Caleonic colouration thus differs from pied colouration in how countershading has been modified. In the latter, pale ventral surfaces have been converted into parts of the large-scale, dark/pale contrast in the pigmentation of the pelage.

It is normal for the ventral parts of the body to be pale, as part of the inconspicuous pattern called cryptic colouration. However, the extension of this pale switches the effect to conspicuousness. This is because the pale, encroaching upwards towards the dorsal side, tends to catch the sunlight at

  • all seasons, and
  • most times of day.

In caleonic colouration, this ‘lateralisation’ of the pale parts of the pelage occurs variously on the

  • cheeks,
  • neck,
  • shoulders,
  • flanks, and/or
  • hindquarters.

Caleonic colouration thus achieves whole-body conspicuousness.

In extreme cases, the 'lateralisation' of pale pelage reaches the dorsal surfaces of the rump, neck, and even back.

In this series of Posts, I hypothesise that a widespread species, the caribou (Rangifer tarandus, https://www.inaturalist.org/taxa/42199-Rangifer-tarandus) has

This arguably makes R. tarandus the only species of mammal in which both patterns (pied and caleonic) occur, depending on the region/subspecies.

The only other species possessing caleonic colouration in only certain populations seems to be the domestic horse (Equus caballus). However, this may have arisen by hybridisation among several wild congeners, during the process of selective breeding (see https://www.inaturalist.org/posts/66546-a-hyperconspicuous-horse-hiding-in-plain-sight#).

The following show pied colouration in R. tarandus:

https://www.alamy.com/caribou-barren-ground-bull-autumn-denali-park-alaska-image219057000.html?imageid=CA708987-0B78-4D58-A301-7570ACD15211&p=365985&pn=3&searchId=8ef83f2f1de0431123cf39602bbd6277&searchtype=0 and https://www.alamy.com/stock-photo-caribou-rangifer-tarandus-bull-with-female-calf-on-migration-south-41499424.html?imageid=24FDBEC7-2515-4910-A5C6-57A0352BEF7C&p=54193&pn=3&searchId=8ef83f2f1de0431123cf39602bbd6277&searchtype=0 and https://www.alamy.com/stock-photo-caribou-rangifer-tarandus-bull-female-in-snow-on-migration-south-through-41499304.html?imageid=013FADBA-BE26-48E8-96CC-B83A1BEDFC74&p=54193&pn=4&searchId=53fe7e947085511a49c95d7dac229e54&searchtype=0 and https://www.alamy.com/caribou-barren-ground-bull-autumn-denali-park-alaska-image219057056.html?imageid=8BFBDFF1-5FE8-4504-BC54-0C1ED673978D&p=365985&pn=4&searchId=53fe7e947085511a49c95d7dac229e54&searchtype=0 and https://www.adfg.alaska.gov/static/home/library/pdfs/wildlife/caribou_trails/caribou_trails_2014.pdf.

The following seem to show caleonic colouration in R. tarandus:

https://www.mindenpictures.com/stock-photo-woodland-caribou-rangifer-tarandus-caribou-male-newfoundland-canada-naturephotography-image00596574.html and https://m.facebook.com/NewfoundlandLabradorTourism/photos/a.111088443781/111092763781/?type=3 and https://www.inaturalist.org/observations/9039103 and https://www.inaturalist.org/observations/91586926 and https://www.inaturalist.org/observations/38196369.

Pied colouration occurs in the autumn coat of most of the subspecies of R. tarandus, including R. t. groenlandicus and R. t. granti. The darkest features are arranged to provide dark/pale contrast, not crypsis or disruption of the outline of the animal.

These dark parts in this pied colouration are

  • muzzle,
  • forelegs,
  • brisket/chest/lower shoulders, and
  • lower flanks.

In the same figures, the palest features are

  • nose (rhinarium),
  • neck,
  • beard/dewlap,
  • tail, and
  • the narrow area of pale on the rump.

In R. tarandus, caleonic colouration seems to occur in the subspecies found on two systems of islands, far apart geographically (https://en.wikipedia.org/wiki/Boreal_woodland_caribou#/media/File:Rangifer_tarandus_Map_NA.svg).

Firstly, on the island of Newfoundland (https://en.wikipedia.org/wiki/Newfoundland_(island)) occurs the subspecies R. t. terranovae (https://www.naturepl.com/stock-photo-woodland-caribou-nature-image00596572.html and https://www.shutterstock.com/de/image-photo/caribou-adult-female-rangifer-tarandus-avalon-1911012163).

Secondly (see part 2 of this series), on the Arctic islands of Canada occurs the subspecies R. t. pearyi (https://www.natureconservancy.ca/en/what-we-do/resource-centre/featured-species/mammals/peary-caribou.html and https://www.inaturalist.org/guide_taxa/1119027 and https://www.enr.gov.nt.ca/en/services/caribou-nwt/peary-caribou and https://www.alamy.com/stock-photo-bull-caribou-in-velvet-antlers-stands-in-the-colorful-autumn-tundra-75290355.html?imageid=89F3DD5C-43FB-48AC-B540-F92A8006B30D&p=228679&pn=25&searchId=9892403e79eeaa448727cb13a1e36c01&searchtype=0).

I agree with Valerius Geist that R. tarandus on the island of Newfoundland is quite distinct from other forms of ‘woodland caribou’, and that taxonomy took a wrong turn when R. t. terranovae was lumped with R. t. caribou.

The ‘woodland caribou’, in the western part of the boreal zone of North America, is unusually dark for the species (e.g. according to Valerius Geist). By contrast, R. t. terranovae is unusually pale - particularly considering that it lives at a far lower latitude than R. t. pearyi.

The following further illustrate R. t. terranovae: https://www.wildandexposed.com/journal/2018/10/17/marks-adventures-in-newfoundland
and https://mobile.twitter.com/NFLDdesigns/status/1339255210749865986/photo/1 and http://www.nlnature.com/Newfoundland-Canada-Nature/1520.aspx and http://birdingnewfoundland.blogspot.com/2009/12/southern-avalon-peninsula-birds-and.html and second photo in https://www.cbc.ca/news/canada/newfoundland-labrador/reindeer-deer-lake-video-1.4918560.

In the pied pattern, the lower flanks, chest, lower shoulders, and brisket are the darkest parts of the figure. This differs from the caleonic pattern in R. t. terranovae, in which these are the palest parts of the figure. Furthermore, a distinctive feature of R. t. terranovae is an individually variable diagonal border between relative dark and relative pale on the haunch (https://www.natureinstock.com/search/preview/woodland-caribou-rangifer-tarandus-caribou-bull-in-town-newfoundland-canada/0_10121446.html and http://conservationbiologynewfoundland.blogspot.com/2012/04/newfoundlands-wilderness-reserves.html).

Detracting from the caleonic pattern is the fact that some individuals of R. t. terranovae have a faint version of the flank-banding seen in other subspecies of R. tarandus.

However, this may perhaps be owing to some degree of anthropogenic mixing with another subspecies.

I hypothesise that the original appearance of the Newfoundland form was truly caleonic, to the exclusion of the flank-banding.

Wilkerson (2010, https://www.mun.ca/biology/scarr/Wilkerson%202010,%20excerpt.pdf) states that the domestic reindeer (R. t. tarandus) was introduced to the island of Newfoundland early in the twentieth century, and that there was indeed contact between this subspecies (which possesses flank-banding) and the indigenous populations, viz R. t. terranovae. I infer the possibility of hybridisation.

It is hard to see how the two patterns of colouration in R. tarandus, namely pied and caleonic, can be represented as extremes on a continuum. Instead, what seems to have happened is that, in an ancestral form,

  • the whitish at the belly has spread so far up that it has replaced the entire flank-band complex of the pied pattern, while at the same time
  • the legs have gone from basically dark to basically pale, and
  • the neck has acquired a darkish dorsal (nuchal) zone.

It is this combination of pale flanks, pale legs, and a dark nuchal area that makes R. t. terranovae a candidate for caleonic colouration. The combination of extension of pale pelage on to flank and haunch, plus an overall pallour, set this subspecies apart from all other subspecies, besides R. t. pearyi.

However, the following three aspects detract from any simple characterisation of the colouration in R. t. terranovae as caleonic:

  • some individuals do retain a faint version of the flank-banding typical of most subspecies of R. tarandus;
  • the pale of the neck tends to be disjunct from the pale of the shoulders and flanks, separated by a more-or-less vertical tract of pale greyish-fawn pelage; and
  • the pale of the lower haunch tends to give way, ventrally, to a darker tone on the upper hindleg, in some individuals.

What this means is that the pattern in R. t. terranovae - at least in its remaining, hypothetically hybridised form - is not categorically different from that in other subspecies.
   
In R. tarandus, any description of adaptive colouration must account for the seasonal cycle, in which the pelage moults. The moulting leads from this appearance (https://www.inaturalist.org/observations/137363786) to this (https://www.inaturalist.org/observations/73867876).

In winter, the pigmentation fades, owing to wear and weathering. The pelage then falls out in early summer, and re-grows from the darkly-pigmented skin. The colouration initially looks fairly uniform, before the full length of the hairs is achieved and the pigmentation differentiates.

Thus, the fully-differentiated colouration tends to be expressed in autumn, corresponding to the rutting season.

The following two male individuals, probably in September, show some features linking the ‘typical’ pattern above to the pattern typical of other subspecies of R. tarandus: https://www.alamy.com/stock-photo-two-caribou-rangifer-tarandus-forage-during-autumn-in-gros-morne-national-43870484.html. These include the relative darkness of the legs and the faint banding on the flank. These detractions notwithstanding, the colouration remains different from those of any other forms of ‘woodland caribou’ at the same season.

I take the following to be an adolescent male individual in autumn: http://www.hww.ca/en/wildlife/mammals/caribou.html. The side of the body shows a faint version of the banding seen in most subspecies of R. tarandus.

WINTER:
January: https://www.inaturalist.org/observations/85723506
March: https://www.inaturalist.org/observations/97411894
April: https://www.inaturalist.org/observations/43119657 and https://www.inaturalist.org/observations/73404224

SPRING:
Early May: https://www.inaturalist.org/observations/4829891 and https://www.inaturalist.org/observations/12796122 and https://www.inaturalist.org/observations/127414114 and https://www.inaturalist.org/observations/147676351
Late May: https://www.inaturalist.org/observations/1535227 and https://www.inaturalist.org/observations/120545240
Early June: https://www.inaturalist.org/observations/59202799 and https://www.inaturalist.org/observations/127339998 and https://www.inaturalist.org/observations/120600128 and https://www.inaturalist.org/observations/30141537 and https://www.inaturalist.org/observations/26703702 and https://www.inaturalist.org/observations/136693452

SUMMER:
Mid-June: https://www.inaturalist.org/observations/72014363 and https://www.inaturalist.org/observations/135072586
Late June: https://www.inaturalist.org/observations/87895806 and https://www.inaturalist.org/observations/69215843
Early July: https://www.inaturalist.org/observations/28248163 and https://www.inaturalist.org/observations/17045792 
Mid-July: https://www.inaturalist.org/observations/14903618 and https://www.inaturalist.org/observations/128037050 and https://www.inaturalist.org/observations/130969801 and https://www.inaturalist.org/observations/2870518 and https://www.inaturalist.org/observations/146311257 and https://www.inaturalist.org/observations/28836472
Late July: https://www.inaturalist.org/observations/8063943
Early August: https://www.inaturalist.org/observations/91586926 and https://www.inaturalist.org/observations/73867876
Mid-August: https://www.inaturalist.org/observations/38196369 and https://www.inaturalist.org/observations/38195578
Late August: https://www.inaturalist.org/observations/33067919

AUTUMN:
Early September: https://www.inaturalist.org/observations/134114763 and https://www.inaturalist.org/observations/65690022
Mid-September: https://www.inaturalist.org/observations/65690664 and https://www.inaturalist.org/observations/75381992 and https://www.inaturalist.org/observations/99568979

The following (https://www.inaturalist.org/observations/28836472) seems to conform to caleonic colouration. However, once one understands the cycle of moult and regrowth of the pelage, it is obvious that the effect results mainly from the fact that the faded coat of the previous year has fallen out from the dorsal part of the figure first (as seen more clearly in https://www.inaturalist.org/observations/126510207).

to be continued in https://www.inaturalist.org/journal/milewski/67534-caleonic-colouration-in-the-caribou-part-2-rangifer-tarandus-pearyi-in-context#...

Publicado el enero 30, 2023 09:12 MAÑANA por milewski milewski | 40 comentarios | Deja un comentario