No evolutionary convergence in mammal communities in southwestern Australia and the southwestern Cape of South Africa, part 2
The mammal community probably originally contained fewer species in the Australian than in the South African site. This is likely notwithstanding the fact that several species of rodents and marsupials with slow reproduction have disappeared from mallee-heath since the anthropogenic introduction of Vulpes vulpes (https://www.inaturalist.org/taxa/42069-Vulpes-vulpes) and Felis catus (https://www.inaturalist.org/taxa/118552-Felis-catus).
Pseudomys shortridgei (https://www.inaturalist.org/taxa/45196-Pseudomys-shortridgei and https://museum.wa.gov.au/sites/default/files/THE%20REDISCOVERY,%20AFTER%2056%20YEARS,%20OF%20THE%20HEATH%20RAT%20PSEUDOMYS%20SHORTRIDGEI%20(THOMAS,%201907)%20(RODENTIA%20MURIDAE)%20IN%20WESTERN%20AUSTRA.pdf), for example, breeds only at one time of year, at an age when most southern African mice of similar size have lived out their lives, with much longer pregnancy and with one-third their numbers of young per litter. Its place today is largely taken by the introduced Mus musculus (https://www.inaturalist.org/taxa/44705-Mus-musculus), which is common after fire.
Macropus fuliginosus (https://www.inaturalist.org/taxa/42881-Macropus-fuliginosus) found in mallee-heath resembles a bovid (Pelea capreolus, https://www.inaturalist.org/taxa/42336-Pelea-capreolus) in surviving on poor forage, which occurs in recently-burnt proteoid fynbos. The times from conception to sexual maturity seem similar, but the pregnancy of the kangaroo is less than one-eighth as long as that of the antelope.
Rodents are fairly common in the few seepage areas and lime-rich dunes adjacent to the Australian study site, but uncommon where the vegetation is low or open, irrespective of landform. The smallest number of species and individuals of rodents and other mammals near the South African study site are found where sands are shallow over quartzite, especially in mature but low and open vegetation.
Mole-rats, including Georychus capensis (https://www.inaturalist.org/taxa/43761-Georychus-capensis), which depends on the fleshy underground storage organs of herbaceous plants, occur at best marginally to proteoid fynbos. However, they occur as small populations on the most fertile soils (loams derived from slate) near the South African study site.
A rat-kangaroo (Potorous gilbertii, https://en.wikipedia.org/wiki/Gilbert%27s_potoroo), which until recently inhabited tall, dense vegetation near the Australian study site, has less than half as many newborns at a time, gives birth half as often per year, and takes more than three times as long to develop from conception to weaning, as an uncommon lagomorph that is its closest counterpart in similar vegetation near the South African study site, and occurs in low, open vegetation.
A large-bodied monkey (Papio ursinus griseipes, https://www.inaturalist.org/taxa/57556-Papio-ursinus) enters proteoid fynbos to supplement its mixed diet.
Other relevant large-bodied ungulates are:
- Taurotragus oryx oryx (https://www.inaturalist.org/observations/6189439),
- Damaliscus pygargus pygargus (https://www.inaturalist.org/taxa/42275-Damaliscus-pygargus), and
- Hippotragus leucophaeus (https://en.wikipedia.org/wiki/Bluebuck).
These were probably originally present in the South African study site - even if only temporarily while visiting from grassy alluvial plains developed over shale fairly nearby - with their attendant predators (e.g. Lycaon pictus, https://www.inaturalist.org/taxa/42093-Lycaon-pictus).
Overall, minimal similarity between continents is apparent, in these mammalian communities. I have not found even a single pair of species-for-species counterparts showing what I can call meaningful evolutionary convergence.
Comments
The community of small rodents of proteoid fynbos in and west of Cape Agulhas National Park is differentiated, containing: Rhabdomys pumilio (https://www.inaturalist.org/taxa/45723-Rhabdomys-pumilio), Steatomys krebsii (https://www.inaturalist.org/taxa/44925-Steatomys-krebsii), Mus minutoides (https://www.inaturalist.org/taxa/44716-Mus-minutoides), Myomyscus verreauxii (40 grams), Otomys spp., and possibly Dendromus melanotis (https://www.inaturalist.org/taxa/44971-Dendromus-melanotis).
The community of small rodents in mallee-heath in Fitzgerald River National Park is rudimentary and undifferentiated by comparison: just Rattus fuscipes (about 60 grams) and two spp. of Pseudomys if Pseudomys albocinereus (about 30 grams, https://en.wikipedia.org/wiki/Ash-grey_mouse and https://terrestrialecosystems.com/wp-content/uploads/2018/03/Barker-et-al-2012.-Thermoregulation-by-an-Australian-murine-rodent-the-ash-grey-mouse.pdf) is/was present in addition to P. shortridgei (about 60 grams, http://www.environment.gov.au/biodiversity/threatened/species/pubs/77-conservation-advice-07122016.pdf and https://en.wikipedia.org/wiki/Heath_mouse#:~:text=within%20the%20species.-,Description,mm%20is%20always%20proportionally%20shorter.).
An extinct species possibly occurring formerly in mallee-heath in Fitzgerald River National Park is Potorous platyops (https://en.wikipedia.org/wiki/Broad-faced_potoroo).
Another possibility is Perameles (https://en.wikipedia.org/wiki/Perameles).
https://library.dbca.wa.gov.au/static/FullTextFiles/018251.pdf
The body length (without tail) of Suncus is only 5.6 cm, whereas the body mass of Hystrix is up to 23 kg.
@ludwig_muller @vynbos @sandraf @henrydelange
Carrick P (1994) Rodents and the Restionaceae: implications of plant-herbivore interactions in the fynbos. Botany Hons project, University of Cape Town.
The study area was Silvermine Nature Reserve (https://en.wikipedia.org/wiki/Silvermine_Nature_Reserve), mid-May to mid-September 1994.
Trapping showed that the rodent fauna in fynbos in the study area included Otomys irroratus (https://www.inaturalist.org/taxa/45437-Otomys-irroratus), Rhabdomys pumilio (https://www.inaturalist.org/taxa/45723-Rhabdomys-pumilio), Acomys subspinosus (https://www.inaturalist.org/taxa/45587-Acomys-subspinosus), Mus minutoides (https://www.inaturalist.org/taxa/44716-Mus-minutoides), and Myomyscus verreauxii (https://www.inaturalist.org/taxa/74689-Myomyscus-verreauxii).
Species of Restionaceae studied were Staberoha cernua (https://www.inaturalist.org/taxa/594701-Staberoha-cernua), Thamnochortus lucens (https://www.inaturalist.org/taxa/544614-Thamnochortus-lucens), Thamnochortus gracilis (https://www.inaturalist.org/taxa/595317-Thamnochortus-gracilis), Hypodiscus aristatus (https://www.inaturalist.org/taxa/557506-Hypodiscus-aristatus), and Willdenowia glomerata (https://www.inaturalist.org/taxa/596271-Willdenowia-glomerata).
The culms (https://en.wikipedia.org/wiki/Culm_(botany)) of these spp. were eaten by O. irroratus. Most preferred (85% of records) was the least sclerophyllous species, S. cernua, and least preferred was T. gracilis (26%). Willdenowia glomerata, which is particularly sclerophyllous, was not preferred.
(My commentary:
I noticed, at Red Hill near Simonstown, October 2001, that S. cernua regenerated particularly rapidly after fire.)
All of the studied spp. of restioids grew in winter, at similar rates, except for the slow-growing (and least-preferred) T. gracilis.
Culms of Restionaceae, which have diameter 1.5-2.7 mm, were cut just above ground level. "Unlike grasses, the meristematic region of restioids is apical, thus grazed material is not easily replaced (Linder, 1991)".
The culms of all these spp. were similar in the concentration of nitrogen: tops of culms 8 mg/g, up to 9 mg/g, bottoms of culms 3-6 mg/g, and bracts 2-3 mg/g. The overall value, 5.5-6.5 mg/g, corresponds to about 3.8% protein. "Thus low nitrogen concentration does not necessarily offer a refuge from grazing in the fynbos".
This is so poor that Grubb (1992, https://agris.fao.org/agris-search/search.do?recordID=US201301768995) regarded herbivory as impossible on such material.
Otomys irroratus foraged wastefully on these restioids, eating only a small proportion of what they cut down.
"Otomys rarely consumed the bases of the culms and were not observed to eat bracts, preferentially feeding on culm tops and other new growth (i.e. new shoots of branching culms) and also eating certain inflorescences (e.g. male H. aristatus)".
Water content was greatest in H. aristatus, and least in the most sclerophyllous species, viz. T. gracilis. The tops and bottoms of culms were similar in water content.
"In fact, it is likely that Otomys is responsible for the majority of mammalian herbivory in mountain fynbos (W Bond, pers. comm.)".
My overall commentary:
Otomys irroratus seems to accept green matter with about 5% protein, recycling the nutrients in its faeces and via the decomposition of wasted cuttings. I infer that consumption of protein-poor greens may also be true for the ungulates indigenous to fynbos, which ranged from Raphicerus melanotis (https://www.inaturalist.org/taxa/42376-Raphicerus-melanotis) to Loxodonta africana (https://journals.co.za/doi/pdf/10.10520/AJA00423203_2578).
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