Αρχεία Ημερολογίου για Ιούλιος 2023

Ιούλιος 05, 2023

Perverse exercise for the growing pelican

Is it possible that pelicans (https://www.inaturalist.org/observations?place_id=any&taxon_id=4323&view=species) routinely use a benign form of family abuse to train the growth of their super-light skeletons and air-sacs (https://en.wikipedia.org/wiki/Air_sac)?

At first sight, it might seem that

  • the infants of pelicans, like other altricial birds, beg vigorously from their parents to demonstrate their fitness to be fed, and
  • this is more conspicuous than in other birds, simply because of the sheer size of pelicans.

However, the situation is odder than this.

Please see:
Scroll through https://www.flickr.com/photos/dougbeckers/5042779690/in/photostream/

Please consider the Australian pelican (Pelecanus conspicillatus, https://www.inaturalist.org/observations/22603013).

Juveniles, after and not before being fed, convulse in what looks like a mad rage, throwing themselves around for a minute, and then collapsing to the ground, before snapping out of it - as if nothing has happened - and settling down to their normal snooze.

Parents of the African white pelican (Pelecanus onocrotalus, https://www.inaturalist.org/taxa/4327-Pelecanus-onocrotalus) seize their half-grown juveniles, and shake them brutally, like a terrier killing a rat, before feeding them.

Later, as if to prove that this is not punishment, the workout becomes self-inflicted as the nearly-fledged juvenile of the African white pelican struggles to withdraw its head from its parent's throat. This is an excruciating ritual to watch, because the beak seems to jam, half-open, in the parent's stomach, and both individuals risk being flailed like rag dolls.

The violence of these fits seems at odds with

  • the intricacy of the body of pelicans, and
  • the touchingly delicate use of the beak-tip to feed the newly-hatched infant.

Pelicans are among the lightest of living birds for their bulk (https://www.lf2.cuni.cz/en/articles/the-legend-of-the-pelican). Consequently, their bones need to have particular resilience.

The hectic experiences of the juveniles of pelicans may therefore be a method of strengthening their growing skeletons and membrane-bound air-sacs.

Posted on Ιούλιος 05, 2023 0455 ΠΜ by milewski milewski | 13σχόλια | Αφήστε ένα σχόλιο

What is the real value of a kidney? part 1

According to textbooks, renal function is no mystery (https://en.wikipedia.org/wiki/Kidney).

It is simply the homeostatic regulation (https://en.wikipedia.org/wiki/Homeostasis) of body fluids, the main mechanism of which is urination of excess water, salts, acids, and nitrogen (https://www.niddk.nih.gov/health-information/kidney-disease/kidneys-how-they-work).

Other organs such as the skin (https://pubmed.ncbi.nlm.nih.gov/24577280/#:~:text=The%20skin%20excretes%20substances%20primarily,metabolism%20and%20excretion%20of%20sweat.) and intestines (https://humanbiology.pressbooks.tru.ca/chapter/18-2-organs-of-excretion/) also contribute to the elimination of potentially toxic wastes from the blood. However, the kidney - according to textbooks - is the only organ, shared by all vertebrates, that is dedicated to excretion.

However, this conventional view is unsatisfactory.

The true electrochemical function of the kidney is deceptive and subtle:

  • 'homeostatic regulation', although valid, is too vague to give an understanding of renal physiology, and
  • 'urination' also falls short, because it is a secondary, rather than primary, function of the kidney.

Clues to the real specialisation of the kidney - which I hypothesise to be the balancing and reformulating of pro-oxidants and anti-oxidants throughout the body - lie in four observations.

Firstly, the intricacy (https://en.wikipedia.org/wiki/Nephron) and energetic cost of the kidney suggest that its true function is more fundamental than any aspect of excretion.

(Please see the four comments below, with the headings 'energy-exorbitance of kidney', parts 1-4.)

The pair of kidneys accounts for only about 0.5% of the mass (https://byjus.com/question-answer/average-weight-of-adult-human-kidney-is-about/), yet uses about 10% of the energy (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4232006/), of the human body. This is disproportionate by a factor of 20.

For comparison, the human brain - although renowned for being energy-expensive - is disproportionate by a factor of only 10.

Indeed, the paired kidneys are so powerful that they reformulate, molecule by molecule, all the blood plasma (https://en.wikipedia.org/wiki/Blood_plasma) of the whole human body every 22 minutes (https://www.ncbi.nlm.nih.gov/books/NBK500032/ and https://www.sciencedirect.com/topics/medicine-and-dentistry/kidney-blood-flow and https://courses.lumenlearning.com/suny-ap2/chapter/physiology-of-urine-formation/).

Secondly, the kidney provides a uniquely neutral environment. This is because

Thirdly, nearly all substances filtered from the blood into the renal tubules (https://en.wikipedia.org/wiki/Glomerular_filtration_rate) are reabsorbed into the blood, with only a small fraction being excreted.

This is partly because urea (https://en.wikipedia.org/wiki/Urea) and uric acid (https://en.wikipedia.org/wiki/Uric_acid), although often assumed to be mere wastes, are

And lastly, most of the true excreta subsequently pass directly from the blood into the urinary tract (https://mcb.berkeley.edu/courses/mcb135e/kidneyprocess.html).

Based on these observations, renal physiology transcends the mere maintenance of ionic balance in the blood via excretion and acid/alkaline buffering.

Instead, diverse molecules can routinely be quarantined - separate from blood and lymph - in a body compartment where electrons can be traded among the intercepted pro-oxidants (https://en.wikipedia.org/wiki/Pro-oxidant), anti-oxidants (https://en.wikipedia.org/wiki/Antioxidant), and ions (https://en.wikipedia.org/wiki/Ion).

In the resulting reformulation, radicals can be processed to optimise the overall effects of redox reactions throughout the body. In this process, the various pro-oxidant and anti-oxidant substances are mixed and matched appropriately.

In this way, homeostasis can be achieved in the precise sense of controlling 'free radicals' (https://en.wikipedia.org/wiki/Radical_(chemistry)), yet retaining enough pro-oxidants of appropriate types to kill cancerous cells and current pathogens.

In summary, the anatomy and function of the kidney are consistent with a dedication as an 'oxido-transformer' for the whole body, balancing the overall costs and benefits of respiration in all organs.

This may be described as the maintenance of homeostasis, but is different from - and incomparably more expensive than - the kind of homeostasis invoked in textbooks.

Does this new interpretation - which I first worked out in 2010 - not better explain the complexity and power of the kidney, based on the realisation that management of the chain reactions of oxidation is the ultimate challenge for aerobic metabolism?

After all, metabolism is identical to combustion, in that both processes take fuels and oxidise them, converting compounds of CHO to carbon dioxide and water. The difference is one of control: metabolism (enzymatic oxidation) promotes cellular function, whereas combustion (non-catalytic oxidation) destroys it.

This difference is so basic to life that nobody should be surprised that an organ is devoted to it. And that organ, I suggest, is the kidney.

to be continued in https://www.inaturalist.org/journal/milewski/81889-what-is-the-real-value-of-a-kidney-part-2#...

Posted on Ιούλιος 05, 2023 0713 ΠΜ by milewski milewski | 26σχόλια | Αφήστε ένα σχόλιο

Ιούλιος 07, 2023

What is the real value of a kidney? part 2

...continued from https://www.inaturalist.org/journal/milewski/81803-what-is-the-real-value-of-a-kidney-part-1#

The following is an explanation of how Dipodomys (https://www.inaturalist.org/observations?place_id=any&taxon_id=44098&view=species), a genus of rodents extremely adapted to arid conditions, manages to produce extremely concentrated urine, without particular metabolic cost.

One needs to understand this energetically cheap mechanism, in order fully to see through the view (stated or implied in all textbooks) that the kidney is mainly an organ of excretion.

For context, I remind readers that Dipodomys is so well-adapted to deserts that it need never drink; it obtains water from its diet of dry seeds, by virtue of the fact that the oxidation of the carbohydrate in the seeds produces carbon dioxide and 'metabolic water'/'oxidation water' (https://www.biologyonline.com/dictionary/metabolic-water#:~:text=Metabolic%20Water-,Definition,as%20carbohydrates%2C%20fats%20and%20proteins.).

My source is pages 168-170 in Schmidt-Nielsen (1964) Desert animals: physiological problems of neat and water. Clarendon Press, Oxford (https://www.amazon.com/Desert-Animals-Physiological-Problems-Water/dp/0486238504 and https://books.google.com.au/books/about/Desert_Animals.html?id=u9k9AAAAIAAJ&redir_esc=y and https://www.abebooks.com/first-edition/Desert-Animals-Physiological-Problems-Heat-Water/30970210856/bd)

"...the structure of the kangaroo rat kidney...is similar to the kidney of other rodents; its size is not unusual, and the number of glomeruli and their size are normal for this size animal".

My commentary:

This establishes that the renal cortex is normal in Dipodomys, and presumably as energetically exorbitant as in other mammals.

Schmidt-Nielsen (1964) goes on to explain that the water-conserving part of the kidney lies in the renal medulla, and that the mechanism of retrieval of water, from the renal tubule back into the bloodstream, depends not on metabolic activity but instead on a counter-current system (https://journals.physiology.org/doi/full/10.1152/ajpregu.00657.2002#:~:text=It%20is%20generally%20accepted%20that,Henle%20and%20collecting%20ducts%2C%20respectively. and https://www.khanacademy.org/test-prep/mcat/organ-systems/the-renal-system/a/renal-physiology-counter-current-multiplication).

Please also see Schmidt-Nielsen, 1981 (https://www.jstor.org/stable/24964421).

This energetically cheap counter-current system consists of a loop in the renal tubule, in which the urine flows in opposite directions, setting up an osmotic gradient. The more arid-adapted the mammal, the longer this loop, and the better-developed the renal medulla.

"Desert rodents, antelope, camel, giraffe...have the greatest relative development of the renal medulla (which contains the loop structure), and animals that have an aquatic habitat such as beavers, water rats, and platypus have a thin medulla and very short loops".

My commentary:

The economical mechanism of conservation of water in the kidney is structural rather than metabolic; the process of reabsorption is thus 'passive' in terms of energy-use, because it uses osmosis instead of 'pumping'. This is in contrast to the mitochondrial activity in the walls of the renal tubules in processing the filtrate within the renal cortex.


Where does this leave us, w.r.t. the conventional view?

If we take the account in Wikipedia (https://en.wikipedia.org/wiki/Kidney) as typical, it is remarkable that the thermodynamic exorbitance of the kidney - which is perhaps its most significant aspect - is not even mentioned.

The conventional view has been perpetuated, from one generation of students to the next, by a combination of

  • ignoring a thermodynamic 'elephant in the room',
  • remaining caught up in detail (the 'reductionist' trap, so familiar in Science),
  • failing to bring together the recent proliferation of research on antioxidant biochemistry and the older research on renology, and
  • continuing to refer in the vaguest way to 'homeostasis'.

It is only when one stands back far enough to see matters in perspective that one realises that, to this day, the main function of one of the most important organs has never been explained in any conventional publication.

More sobering: a suitable resolution seems to be nowhere on the horizon, in the peer-reviewed literature.

Posted on Ιούλιος 07, 2023 1054 ΜΜ by milewski milewski | 3σχόλια | Αφήστε ένα σχόλιο

Ιούλιος 09, 2023

Why is paternal lactation commoner in birds than in mammals?

Lactation occurs in both birds and mammals, albeit by means of completely different anatomical structures and physiological processes (https://en.wikipedia.org/wiki/Crop_milk).

The analogy is strong, despite the weakness of homology.

However, there is an apparent paradox, as follows.

It is mammals in which lactatation is definitive to the Class. By contrast, lactation occurs only in three orders of birds (Columbidae, Phoenicopteridae, Spheniscidae).

Yet it is in birds that paternal lactation is more common.

In mammals, paternal lactation has been recorded in only three species, all bats (https://en.wikipedia.org/wiki/Male_lactation#:~:text=of%20this%20trait.-,Nonhuman%20animal%20male%20lactation,the%20nursing%20of%20their%20infants.), all belonging to Pteropodidae.

By contrast, in birds paternal lactation is recorded (or assumed) in all of the 344 species of columbids (https://en.wikipedia.org/wiki/Columbidae), all of the six species of phoenicopterids (https://en.wikipedia.org/wiki/Flamingo#Feeding), and one species of spheniscid (https://en.wikipedia.org/wiki/Emperor_penguin).

How can this anomaly be explained?

Let us set aside the case of the emperor penguin, because this species is ecologically and socially extreme, to a degree paralleled by no mammal, or even any other bird.

In the case of columbids and phoenicopterids, the breeding pair is monogamous, and the father lactates along with the mother. This degree of paternal feeding of the offspring does not occur in even the most extremely adapted mammals, such as Lycaon pictus (https://en.wikipedia.org/wiki/African_wild_dog), in which all adult male individuals in the group assist in the care of the litter of the breeding pair, but lactation is absent in males

My explanation is as follows.

In mammals, lactation tends to be associated with a gain in body mass. This is both in the mammae themselves, which tend to store milk to some degree between bouts of suckling (extreme in e.g. Crocuta crocuta), and in the gastrointestinal tract, which tends to hypertrophy in order to meet the lactational needs.

By contrast, in columbids, the parents tend to fast during lactation, and there is no analogue for a full udder.

This is consistent with a fundamental difference between the classes: in birds there is a premium on somatic lightness, in aid of extreme mobility (usually but not necessarily volant).

Because it is essential for birds to remain as light as possible, it is adaptive for the lactational burden to be shared between males and females.

Pteropodid bats are not as evolutionarily committed to mobility as are most birds. However, the fact that the few instances of paternal lactation occur in volant mammals would seem to support my rationale, in the sense of a kind of evolutionary convergence.

Posted on Ιούλιος 09, 2023 1137 ΜΜ by milewski milewski | 2σχόλια | Αφήστε ένα σχόλιο

Ιούλιος 10, 2023

How baboons and like-size, coexisting gazelles differ in their most basic anti-predator strategies, part 2

...continued from https://www.inaturalist.org/posts/62960-how-baboons-and-like-size-coexisting-gazelles-differ-in-their-most-basic-anti-predator-strategies-part-1#

Sympatric Thomson's gazelle and olive baboon show the great variation in pace of life in mammals, hence the different potentials of prey species to support predators.

These two species both

  • weigh about 20 kg,
  • have similar metabolic rates, and
  • bear about a dozen offspring per lifetime.

However, the gazelle breeds three-fold as rapidly as the primate does, as shown by

  • time from conception to earliest birth (16 months vs 4 years),
  • time from birth to weaning (6 months vs 18 months),
  • time from birth to social maturity (males: 3 years vs 9 years), and
  • time between subsequent births (9 months vs 25 months).

Accordingly, Thomson's gazelle lives only a third as long as does the olive baboon (15 years vs 45 years). (Note that the olive baboon lives about as long as does Hippopotamus amphibius, despite the great difference in body mass.)

I infer that this gazelle, a ruminant, spends energy more rapidly (3-fold) on reproduction and growth than does this monkey - making this energy available to predators.

The productivity and the abundance of gazelles both help to sustain the cheetah.

Thomson's gazelle eats grass and other herbaceous leaves, which are

  • abundant compared to the fruits, tubers, flowers, and small animals eaten by the olive baboon, and
  • digested more thoroughly by the ruminant - with its thoroughly fermentative digestion - than by the monogastric primate (partly because Thomson's gazelle rechews its food by night, while the olive baboon sleeps).

Then same density of population of gazelles and baboons can support 3-fold the offtake by predators in the case of this gazelle - hence the potential for a specialised carnivore, living at small densities of population, in the form of the cheetah. This baboon seems as limited as marsupials in its productivity and ability to support predators.

Posted on Ιούλιος 10, 2023 1233 ΠΜ by milewski milewski | 1 σχόλιο | Αφήστε ένα σχόλιο

In the Karoo of South Africa, do plants with succulent fruits have foliage rich in potassium relative to nitrogen?

(writing in progress)

I have observed that succulent fruit-pulp is rich in potassium relative to other nutrients (https://www.inaturalist.org/journal/milewski/72763-why-are-fleshy-fruits-rich-in-potassium# and https://www.inaturalist.org/journal/milewski/63113-why-are-lauraceous-fleshy-fruits-potassium-rich-despite-being-non-succulent#).

If so, do plants with succulent fruits have foliage unusually rich in potassium relative to nitrogen?

I have previously found that plants with fleshy fruits have foliar concentrations of: potassium >1.9
%, nitrogen >1.5%.

ratios of potassium/nitrogen

In this Post, I test this by reviewing the values reported in the literature, for the Karoo (https://en.wikipedia.org/wiki/Karoo) in South Africa.

My finding is that the answer is no. This is perhaps partly because plants with succulent fruits in the Karoo are rich in nitrogen, relative to other ecosystems.

Then following is a summary of the mean percentages (concentration on a dry matter basis), by categories. In each case the numerator refers to potassium, and the denominator refers to nitrogen.

GRASSES 1.0/1.3
DAISIES 1.5/1.0
LEGUMES 1.0/2.2

My commentary:
Plants with succulent fruits, of which Lycium is an example, have foliage that is rather rich in potassium. However, the corresponding concentrations of nitrogen are also rather great. Thus, the ratio of potassium to nitrogen remains modest.

Asteraceae in Karoo:

98 samples

Crude protein mean 9.58%
Nitrogen mean 1.53%
Potassium mean 1.52%
Potassium/nitrogen ratio 0.99

Legumes in Karoo

6 samples

Crude protein mean 13.73%
Nitrogen mean 2.2%
Potassium mean 0.96%
Potassium/nitrogen ratio 0.44

Grasses in Karoo

49 samples

Crude protein mean 7.826%
Nitrogen mean 1.252%
Potassium mean 0.9844% (range 0.14-3.79%)
Potassium/nitrogen ratio 0.786


In Karoo vegetation, potassium/nitrogen ratios are succulent foliage > daisies > grasses and plants with succulent fruits > legumes.

It is remarkable that virtually no legume has a succulent has succulent foliage or fruits, and part of the explanation may be the limited ration of potassium to nitrogen in legumes. This also holds for nitrogen-fixing plants generally.

Daisies seem to be poor in protein, possibly even more so than grasses. This may help to explain

  • their general unpalatability to browsers, and
  • their acceptability as bulk food to Merino sheep, which are basically grazers.

However, they are certainly not poor in potassium. The concentrations of potassium in the leaves of daisies in Karoo vegetation are consistent with the textures of the foliage.



Lycium is a protein- and potassium-rich non-legume.

It is rich in potassium compared to most coexisting plants other than succulents (which average slightly more than 2%) in the Karoo, with values double those in coexisting grasses and legumes. This is consistent with the fleshiness (semi-succulence) of the leaves.

However, the ratio of potassium to nitrogen is small in Lycium, because of its richness in nitrogen.

Foliar concentrations of potassium are slightly less than 2% in the Karoo, compared to about 2% in Australia, and 3-6% in the USA. The latter values seem remarkably great in absolute terms.

In the Karoo, foliar nitrogen, even when underestimated by analysis for crude protein, is 2.8% in Lycium. This is somewhat greater than expected for an intercontinental genus of base-rich soils under semi-arid climates. It exceeds the means for the following categories of plants in the Karoo:

  • plants with succulent fruits (2.4%),
  • legumes (2.2%),
  • succulents (1.8%),
  • grasses (1.3%), and
  • daisies (1.0%).


Atriplex seems typical of succulent plants in its ratio of potassium to nitrogen

Posted on Ιούλιος 10, 2023 0628 ΠΜ by milewski milewski | 5σχόλια | Αφήστε ένα σχόλιο

Modes of dispersal and sowing in woody vegetation in Tongaland, southern Africa

(writing in progress)

On 10 March 1993, I discussed the vegetation in Tongaland with Ken Tinley, who had extensive experience in the field in that region.

The following is the summary of my thoughts, that I noted at the time.

In general, sandynsoils tend to be more suitable for plants with fleshy fruits than are dense clays.

Sodicity and waterlogging are inimical to potassium nutrition and the bearing of succulent fruits.

Mangroves, the souks of which are acidic here, are devoid of succulent fruits.

Swamp forest on nutrient-poor soils (not on floodplains) has relatively few plants with succulent fruits.

Well-drained termite mounds, in which sodicity is restricted to the apron (basal ring), bear stands of plants thoroughly dominated by species with succulent fruits, except for trees, which enter late in succession, when potassium-demanding, smaller plants are already established. These soils are base-rich and presumably rich in potassium, and only mildly sodic overall. They are well-drained despite often having moist subsoils.

In thickets in Tongaland, endozoochorous plants contribute >90% to the vegetation, whether by species or by individuals. However, some of these are euphorbs, which lack fleshy fruits but seem to be devioisnin getting doves to eat them with no obvious benefit to the birds (possibly grind-stones?).

Where the matrix consists of dark cracking clay, which is sodic, even thickets on the mounds tend to lack species with succulent fruits.

Stratification is important, with trees tending not to have succulent fruits. In most vegetation types, the understorey has more plants with succulent fruits than does the canopy. It may be no coincidence that vegetation with an open canopy and a well-developed understorey, such as that dominated by caesalpinioid legumes, have few plants with succulent fruits, because the two strata compete for potassium.

(However, this is somewhat contradicted by the fact that, in savanna, plants withnsucculent fruits tend tomoccur around the bases of big trees.)

This leads to the prediction that big trees should generally only bear succulent fruits where the canopy is dense and shade-casting. This seems to fit the pattern in Sapotaceae, which are prominent in the study area.

The roles of nitrogen-fixing and parasitic plants seem typical. The former tend to have ballistic and/or anemochorous fruits. However, one species of Morella may have succulent fruits.

This study area sheds little light on the role of fire. I expect succulent fruits to be commoner in fire-free than in fire-prone vegetation. However, dry forest in Tongaland has few plants with fleshy fruits, possibly because the soil is leached and trees dominate.

By numbers of individuals, not numbers of spp.:

Tongaland dry forest

forms patches, surrounded by savanna (perhaps can be thought of as 'fire-free miombo')

rainfall 300-1000 mm

duplex sands or ultrafine sands


Flora rich and specialised

The incidence of succulent fruits decreases with height above ground.

A few spp. of ballistically dispersed trees dominate the canopy (60% of individual trees). Species with succulent fruits contribute little (4%) to the tree individuals here. However, more than half of the plants in the understory are zoochorous, despite the prominence of Acanthaceae and Euphorbiaceae, and the inclusion of juveniles of mid-stratum leguminous trees.

By numbers of individual plants

  • canopy 4% zoochorous (but many spp., e.g. of Mimusops and Ficus), 60% ballistic, 20% anemochorous
  • mid-stratum (dominated by Millettia and Craibia) 20% zoochorous (very many spp.), 80% ballistic
  • understorey (dominated by Acanthaceae and Euphorbiaceae, bit including juveniles of legumes) 57% zoochorous, 43% ballistic

By numbers of spp.

  • canopy 40% zoochorous, 20% ballistic, 40% anemochorous
  • mid-stratum 90% zoochorous, 10% ballistic
  • understorey 20% zoochorous, 78% ballistic

Fire-free thickets on termite mounds in a matrix of Senegalia nigrescens, adjacent to dry forest. These mounds have gravelly, sandy, non-sodic clays, and bear stands in which almost 90% of the plants have succulent fruits.

Small patches of lawn of Cynodon (or even Sporobolus, where sodic) occur around the semi-sodic perimeter. The more sodic mounds tend to have sparse thickets. Sodic rings at the bases of mounds tend to form on duplex montmorillonitic soils with a darkmappearance.

Zoochorous plants contribute >90% of spp. and >90% of individuals.

Typical: Mimusops, Cleistochlamys (https://www.inaturalist.org/taxa/340207-Cleistochlamys-kirkii), Trichilia, Diospyros, Cordia, Strychnos, Berchemia.

Anemochorous in the stands on termite mounds: Philenoptera, Combretum, Dalbergia, Markhamia

On most of the termite mounds there occur also various genera of Euphorbiaceae


In Tongaland, forest on termite mounds has a greater incidence of plants with succulent fruits than does the adjacent dry forest. Dispersal and sowing by birds can be achieved without succulent fruits (e.g apparent deception in euphorbias). Thus, the incidence of succulent fruits is not simply a matter of the mechanics of succession and colonisation. Within stands (e.g. dry forest), plants withnsucculent fruits prefer the understorey over the canopy. Even in termite miunds, I suspect that the largest plants tend not to bear succulent fruits.

I infer that termite mounds are near-ideal for zoochorous plants, because they are

  • base-rich (including potassium) and well-drained, but generally not sodic,
  • often protected from fire, but
  • unfavourable for nitrogen-fixing plants, partly because they tend to be relatively rich in nitrogen, and not particularly rich in phosphorus.

Dry forest seems to be too poor in potassium for plants with succulent fruits. In this type, the mkd-stratum is richer than the canopy, in plants with succulent fruits.

Posted on Ιούλιος 10, 2023 0811 ΠΜ by milewski milewski | 1 σχόλιο | Αφήστε ένα σχόλιο

Ιούλιος 11, 2023

Modes of dispersal and sowing in the woody plants of Gorongosa

(writing in progress)


The following refer to woody plants taller than 3 m; by numbers of spp., not individuals.

Miombo canopy consists of about six spp., most being ballistic. Brachystegia is dominant, Julbernardia, Millettia, also ballistic (seeds strike other tree boles)
Mesic Miombo 50% zoochorous (e.g. Rubiaceae), 42% anemochorous, 7% ballistic
Xeric Miombo 18% zoochorous, 78% anemochorous (e.g. Combretum), 3% ballistic

Ken believes that soil moisture is responsible, in miombo

Succession on termite mounds:

  • initially dominance by sun-loving spp., e.g. some spp. of Manilkara or Mimusops (occurring in savanna or forest, wherever there are perch-sites, not necessarily termite mounds)
  • next, in moist areas, bird-dispersed spp. of forest enter under the shady canopy
  • finally, these grow through, and the original sun-loving trees die, leading to fire-free patches of forest with succulent fruits. The spp. entering the upper canopy do not all possess succulent fruits, they tend to be anemochorous (seeds blown from adjacent areas, intercepted by thicket on termite mound, germinate, grow through as replacers). Only some of the canopy trees (e.g. "Chrysophyllum') are zoochorous. Initial heliophytic guild of trees cedes to shade-loving trees with succulent fruits (relatively low plants, in the mid-lower stratum), these grow up while being partly replaced by spp. lacking succulent fruits. Change to shade-loving or thicket understorey birds, i.e. different birds performing the roles of dispersing seeds: Pycnonotus followed by Andropadus and Phyllastrephus. First are clump-adapted, including Treron and frugivorous hornbills, great movers and establishers. Second groupmare more static, multiplying the forest elements, their preferred foods, by their own activities. First, establishment, second, multiplication.

Slopes of Gorongosa mountain:

  • pediment thickets 62% zoochorous, 22% anemochorous, 17% ballistic
  • scrub thicket 55% zoochorous, 37% anemochorous (Vachellia/Senegalia, Albizia, Brachylaena, Dombeya), 7% ballistic

Montane thicket (Buddleia, Philippia https://www.inaturalist.org/taxa/637251-Erica-hexandra, Widdringtonia https://www.inaturalist.org/taxa/135521-Widdringtonia-nodiflora, Nuxia https://www.inaturalist.org/taxa/340348-Nuxia-oppositifolia) 70% zoochorous, 4% anemochorous

Montane forest 85% zoochorous, distributed through all strata

Transitional forest (two-thirds of the way down the mountain) 65% zoochorous, 18% ballistic (e.g. Millettia stuhlmannii, https://www.inaturalist.org/taxa/339372-Millettia-stuhlmannii)

Tropical forest (Newtonia buchananii https://www.inaturalist.org/taxa/133937-Newtonia-buchananii and 'Teleopsis murch') 75% zoochorous, 25% anemochorous

Riverine forest (not the same as swamp forest, which is oligotrophic) 70% zoochorous, 18% anemochorous (among canopy trees, e.g Albizia, whi hnhas light pods that split to expose the seeds, without throwing them out, similarly to Vachellia seyal)

Swamp forest (black-water system, waterlogged and anaerobic)(not the same as riverine forest):

Breonadia salicina https://www.inaturalist.org/taxa/429244-Breonadia-salicina is dominant (mode of dispersal uncertain)
Barrington racemosa https://www.inaturalist.org/taxa/196659-Barringtonia-racemosa is subdominant
Synsepalum brevipes https://www.inaturalist.org/taxa/867589-Synsepalum-brevipes third in abundance zoochorous (birds) fruits succulent but mucilaginous and borne in small quantity
Parkia https://www.inaturalist.org/taxa/133527-Parkia-filicoidea (pollinated by bats)
Khaya uncommon (elsewhere a big tree on river banks) anemochorous
Syzygium guineense zoochorous
Bridelia micrantha yellow fruits similar to Celtis (one of the few euphorbs with succulent fruits)
Homalium https://www.inaturalist.org/taxa/587545-Homalium-dentatum possibly zoochorous
Ficus zoochorous
Erythroxylon red succulent fruit in understorey
Craterispermum https://www.inaturalist.org/taxa/473302-Craterispermum-schweinfurthii

Almost all of the thicket and forest types of the Gorongosa area have mainly animal-dispersed woody spp. However, in drier, presumably more fire-prone types, e.g. miombo, <50% of the woody spp. are animal-dispersed. In dry savanna woodland with e.g. Combretum, only 18% of woody spp. are animal-dispersed (and presumably an even smaller percentage have succulent fruits). Here, ballistic and wind-dispersal predominate in the canopy. The incidence of succulent fruits is also small in oligotrophic swamp forest - in sharp contrast to nearby forest on termite mounds. The incidence of succulent fruits is greatest in forest on remote mounds.

Posted on Ιούλιος 11, 2023 0215 ΠΜ by milewski milewski | 0σχόλια | Αφήστε ένα σχόλιο

Ιούλιος 12, 2023

Nutrient ratios in the foliage of plants in southwestern Western Australia

(writing in progress)

Source: Foulds (1993, https://nph.onlinelibrary.wiley.com/doi/10.1111/j.1469-8137.1993.tb03901.x and https://pubmed.ncbi.nlm.nih.gov/33874598/and https://www.jstor.org/stable/2558261).


Categories of plants in which the foliar concentrations of nitrogen (on a dry matter basis), in decreasing order:
legumes 1.5%
zamia 1.45%
daisies 1.25%
drosera 1.1%
grasses 0.98%
casuarinas 0.81%
restioids 0.8%
types 0.8%

My commentary:

The foliage of Drosera, which supplement nitrogen by consuming insects, is not particularly rich in nitrogen. However, the nitrogen-fixation of legumes does result in nitrogen-richness. Rather than merely compensating for a shortage of nitrogen in the soil, they recharge the ecosystem with this nutrient.


Plants with succulent foliage but non-succulent fruits (excluding parasitic plants)

Plants with succulent foliage and succulent fruits

Plants with succulent fruits but not succulent foliage

Parasitic plants with succulent foliage


The expectation is upheld that foliar concentrations of nitrogen in nitrogen-fixing plants exceed those in 'normal' plants (e.g. grasses and daisies) - if one considers that no grass or daisy is as scleromorphic as some of the legumes, casuarinas, and zamia. In other words, the inability of most grasses and daisies to adapt to extremely poor soils makes a simple comparison difficult. So, I think that nitrogen-fixing plants do indeed have nitrogen-rich foliage, and the small values for casuarinas reflect their sclerophylly and their relatively inefficient systems of nitrogen-fixation. Grasses and daisies have greater foliar concentrations of potassium (1.3-1.6%) than do Western Australian legumes, zamia, drosera, and particularly casuarinas. I interpret this as reflecting not basically different nutrient-content in these groups, but rather their different soils. So I think that the reason why the foliar ratios of potassium/nitrogen in nitrogen-fixing plants are less than those of grasses and daisies is a difference in nitrogen rather than in potassium.


legumes in southwestern Australia (Acacia and Papilionoideae)

mesophyllous (soft-leafed) spp.:

sample 21
foliar potassium mean 1.06%
foliar nitrogen mean 1.9%
potassium/nitrogen ratio 0.56

extremely sclerophyllous spp.:

sample 21
foliar potassium mean 0.675%
foliar nitrogen mean 1.24%
potassium/nitrogen ratio 0.54

My commentary:
The foliar concentration of potassium in mesophyllous spp. of legumes is similar to that in the Karoo (about 1%). The ratios do not differ between mesophyllous and extremely sclerophyllous legumes, despite the fact that the latter are the poorer in both elements.

Eutrophic-type legumes do seem to exceed oligotrophic legumes in foliar concentrations of nitrogen (1.9% vs 1.24%). A similar relationship applies to potassium (1.1% vs 0.7%). In both cases the difference is 1.5-fold.

However, the ratios of potassium/nitrogen do not differ: about 0.55 in both cases, which is also similar to that for legumes in general in southwestern Australia. These plants, although diverse phylogenetically and morphologically, are homogeneous in terms of the foliar ratios kf potassium/nitrogen.

particularly sclerophyllous Proteaceae (Banksia and Hakea) in southwestern Australia:
sample size 79
foliar potassium mean 0.4%
foliar nitrogen mean 0.61%
potassium/nitrogen ratio 0.66

My commentary:
The ratio is small, comparably so to nitrogen-fixing legumes. This is because extreme sclerophylly is associated with extreme foliar poverty of potassium.


Parasites with fleshy foliage (few spp. available, restricted to mistletoes and orobanche)
Amyema 15.5/6.5, Lysiana (is the foliage really fleshy?) 12.9/14.7, Orobanche 25/8.1
potassium mean 1.78%
nitrogen mean 0.98%
ratio 1.8 (a surprisingly great value)

My commentary:
Note the extreme potassium-richness in Orobanche
Parasites with fleshy foliage: ratio is 3-fold greater than for casuarina and zamia (both of which are nitrogen-fixers) and drosera.

The sample is small. However, these preliminary results do seem in line with plants in general, w.r.t. foliar concentrations of potassium relative to foliar texture. It seems that parasites do not have greater foliar concentrations of potassium than expected for their foliar textures; it is just that their foliage is fleshier than expected for the soils on which their hosts grow.

So, if the foliar ratios of potassium/nitrogen parasites are boosted, this is possibly because of foliar poverty in nitrogen.

GRAMINOIDS (grasses, restios, and cypes)


sample 15
potassium 1.32%
nitrogen 0.98%

restios and cypes
sample 22
potassium 0.65%

sample 18
potassium 0.7%
nitrogen 0.8%
ratio 0.86

My commentary:

Surprisingly, restios are much poorer than grasses in potassium, but only slightly poorer in nitrogen.

It is clear that all graminoids have 'foliar' concentrations of nitrogen of about 0.8-1% - less in the sclerophyllous spp., in which it is the stems, not the leaves, that have been analysed. However, the values for potassium vary greatly: restios have less than half the concentrations of potassium found in grasses. Is this simply explained by foliar hardness/softness, an extension of my rationale w.r.t. succulence?


sample 31
potassium 1.6%
nitrogen 1.25%


Potassium/nitrogen ratios:

  • plants with succulent foliage about 1.44 (recalculate); those without succulent fruits 1.13, those with succulent fruits 1.88
  • nitrogen-fixing plants and carnivorous plants 0.5 up to 0.7 (generally 0.55-0.65)
  • legumes (large sample, so value is reliable) 0.54
  • casuarinas 0.55 (good agreement)
  • zamia (one species, 4 samples) 0.62
  • drosera (one species, 3 samples)

My commentary:

All plants with succulent foliage have great ratios of potassium/nitrogen, but those with succulent fruits as well (e.g. Chenopodium/Rhagodia) have the greatest ratios.

Plants with succulent foliage, none of which are nitrogen-fixers, have foliar ratios of potassium/nitrogen >2.5-fold those of nitrogen-fixing plants (and a carnivorous plant).

Compare parasitic plants with plants with succulent foliage (small sample) 1.8, which agrees with succulent plants with succulent fruits. The mistletoes sampled do not have truly succulent foliage, and the orobanche lacks succulent fruits, but these plants have supplementationnof potassium, boosting their ratios of potassium/nitrogen nearly to the level of non-parasitic plants combining succulent foliage and succulent fruits.

Posted on Ιούλιος 12, 2023 1115 ΠΜ by milewski milewski | 1 σχόλιο | Αφήστε ένα σχόλιο

Ιούλιος 13, 2023

Plasticfruits, part 5: the case of Dioscorea (Dioscoreaceae)

@mjpapay @jayhorn @sedgesrock @graham_g @robertarcher397 @nicky @ludwig_muller @jeremygilmore @tonyrebelo @botaneek @troos @adriaan_grobler @zorille @bobwardell @carber @yvettevanwijk1941 @margl @kelsey414

...continued from https://www.inaturalist.org/journal/milewski/73269-plasticfruits-the-case-of-chenopodium-amaranthaceae#

The herbaceous genus Dioscorea (https://link.springer.com/chapter/10.1007/13836_2021_94 and https://biblio.iita.org/documents/U11InbkBhattacharjeeDioscoreaNothomDev.pdf-61e9e4ea95947bbb95aa36658f29059c.pdf) contains more than 600 spp.

It occurs on all vegetated continents, and many islands (please scroll to map in http://sanjeetbiotech.blogspot.com/2012/11/dioscoreaceae-family-of-flowering.html).

There is significant variation in the vegetative features. For example:

However, the variation in the fruits of Dioscorea is extreme (https://idtools.org/seed_families/index.cfm?packageID=1140&entityID=5525).

Many spp. are 'doubly-adapted for dispersal by wind, by virtue of wings on both the fruits and the seeds; by contrast, a few are so clearly adapted for dispersal in the gastrointestinal tracts of birds that they were formerly assumed to constitute a separate genus (Tamus).


A clade of spp. in Brazil, in which the plants are short, has round, wingless capsules (https://www.biotaxa.org/Phytotaxa/article/view/phytotaxa.163.4.3 and https://www.scielo.br/j/hoehnea/a/jvRrZ6KKC5rYwx7bXfk96sF/?lang=en&format=html and https://link.springer.com/article/10.1007/s12225-016-9635-8).

Most of the sections and spp. of Dioscorea bear winged, dehiscent capsules, containing seeds that

The following show the winged, dehiscent capsules in various spp. in Australia, Asia, and North America:

Also please see http://www.namethatplant.net/picpage.shtml?path=/Images/ImagesFire/s0/s071011_ab2.jpg&plant=476&photo=8077 and http://www.namethatplant.net/plantdetail.shtml?plant=476.


One section (Rajania, restricted to the Caribbean islands) has samaras (https://www.biorxiv.org/content/10.1101/224790v1.full and https://en.wikipedia.org/wiki/Samara_(fruit) and https://www.plant-ecology.com/EN/10.17521/cjpe.2018.0053 and https://www.inaturalist.org/taxa/914933-Dioscorea-cordata) instead of capsules (https://plants.jstor.org/stable/10.5555/al.ap.specimen.k000099322 and https://plants.jstor.org/stable/10.5555/al.ap.specimen.k000099330).


Most relevant for this Post, one 'infragenus', namely Tamus, has succulent, bright-hued fruits (https://www.inaturalist.org/observations/168975065), and several other clades within Dioscorea also have fleshy fruits, or fruits intermediate between dehiscent capsules and fleshy fruits (e.g. Dioscorea ovinala and Dioscorea anataly of Madagascar, https://www.ingentaconnect.com/content/aspt/sb/2005/00000030/00000004/art00005 and https://www.researchgate.net/publication/250054391_A_Plastid_Gene_Phylogeny_Of_the_Yam_Genus_Dioscorea_Roots_Fruits_and_Madagascar).

The best-known examples are Dioscorea communis (https://www.inaturalist.org/taxa/82691-Dioscorea-communis) and Dioscorea orientalis (https://www.inaturalist.org/taxa/496089-Dioscorea-orientalis), which occur in the Canary Islands and Madeira (https://en.wikipedia.org/wiki/Macaronesia), Europe, the Maghreb, the Caucasus, and the Levant.

It is remarkable enough that a single genus stretches from samaras (with specialised dispersal of the diaspore by wind) to fleshy fruits (with specialised dispersal and sowing by birds).

However, what is particularly remarkable is that the variation in fruit-form cuts across the clades within the genus. This suggests that variation in fruit-form has arisen independently, in the evolutionary process, repeatedly within Dioscorea.

Dioscorea communis and D. orientalis, bearing red berries attractive to seed-dispersing birds, are most closely related to section Borderea, in which the fruits are capsules, containing seeds that lack wings (https://academic.oup.com/aob/article-abstract/131/4/635/6995440?redirectedFrom=fulltext&login=false and see Fig. 2a, on page 190, in https://www.jstage.jst.go.jp/article/apg/71/3/71_202003/_pdf).


In summary, fleshy fruits within Dioscorea are clearly-defined morphologically and adaptively, but poorly-defined phylogenetically. This further exemplifies the evolutionary plasticity of fruits within genera worldwide - which is the focus of this series of Posts.


Dioscorea communis:


Dioscorea orientalis:


Posted on Ιούλιος 13, 2023 0321 ΠΜ by milewski milewski | 21σχόλια | Αφήστε ένα σχόλιο