A new interpretation of the evolutionary and ecological strategy of whiteyes/silvereyes (Zosterops), part 2: a nectarivorous species (Z. chloronothos) as an exception proving a rule

...continued from https://www.inaturalist.org/journal/milewski/95051-a-new-interpretation-of-the-evolutionary-and-ecological-strategy-of-whiteyes-and-silvereyes-zosterops-part-1#

In general, the genus Zosterops has combined great speciation with minimal adaptive radiation.

This is explained partly by the facts that

Zosterops is capable of inhabiting islands as small as one square kilometer, and
most of the species are restricted to islands of various sizes, up to the size of Madagascar, New Guinea, and mainland Australia.

In other words, speciation in Zosterops has been nominal, with minimal modification of a morphological kind.

In this Post, I explore one example - on the island of Mauritius in the Indian Ocean - in which two sympatric spp. of Zosterops have separated in terms of diet.

This example is 'an exception that proves a rule', in the sense that

there is a clear specialisation in nectar in one of the spp., including a significant lengthening of the beak, but
the adaptation has been more behavioural than morphological, i.e. it reflects a change in 'software' rather than 'hardware'.

References:

https://sora.unm.edu/sites/default/files/journals/auk/v088n01/p0035-p0060.pdf

https://onlinelibrary.wiley.com/doi/abs/10.1046/j.1365-2699.2002.00720.x

Zosterops chloronothos (https://earthlife.net/mauritius-olive-white-eyes/Mauritius), which is naturally restricted to Mauritius, has

body size no greater than in most spp. of Zosterops, but
a beak 20% longer (https://www.inaturalist.org/observations/36290310) than expected for this genus.

The diet is mainly nectar and flying insects. Fleshy fruits and gleaned insects, normally part of the diets of Zosterops, are hardly taken by Z. chloronothos.

Zosterops chloronothos is not merely a 'cheat' in the sense of taking nectar without pollinating the plants. Unusually for its genus, it also collects pollen on the forehead.

Plant spp. possibly pollinated by Z. chloronothos (https://www.perplexity.ai/search/Which-plants-indigenous-2OJN2oIbQ2eGSNt0negoIQ) include

Eugenia spp. (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:326088-2), e.g. E. orbiculata,
Sophora denudata (https://upload.wikimedia.org/wikipedia/commons/6/66/Sophora_denudata_%28flowers%29.JPG)
Hypericum spp. (https://www.jstor.org/stable/4113721 and https://en.wikipedia.org/wiki/Hypericum), and
Sideroxylon spp. (https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:326088-2 and https://www.inaturalist.org/observations?taxon_id=1067743 and https://www.inaturalist.org/observations?verifiable=true&taxon_id=969819).

https://www.sciencedirect.com/science/article/pii/S0254629918322725

https://www.biodiversitychallengefunds.org.uk/documents/DAR15038/21379/15-038%20FR%20Ann5.3%20Newsletter%2011%20Aug%202008.pdf

I interpret the nectarivory of Z. chloronothos as follows.

On one hand, it is true that

Z. chloronothos deviates from the norm in its emphasis on exudates (nectar and sap), to the near-exclusion of other dietary components normal in its genus, viz.
fleshy fruit-pulp, and
insects, such as Homoptera (https://en.wikipedia.org/wiki/Homoptera), gleaned from plants.

On the other hand, it is also true that

the morphological modification is so limited that it is hardly noticeable without detailed scrutiny, and
the flowers presumably pollinated by Z. chloronothos have short stamens compared to the typical syndrome of ornithophily (https://www.researchgate.net/profile/Robert-Tropek/publication/352379905_Bird_pollination_syndrome_is_the_plant%27s_adaptation_to_ornithophily_but_nectarivorous_birds_are_not_so_selective/links/60c79a2e299bf108abd9453d/Bird-pollination-syndrome-is-the-plants-adaptation-to-ornithophily-but-nectarivorous-birds-are-not-so-selective.pdf and https://ri.conicet.gov.ar/bitstream/handle/11336/14512/CONICET_Digital_Nro.16781.pdf?sequence=1&isAllowed=y).

What this means is that the deviation from the norm in Z. chloronothos is open to interpretation. It is simultaneously true that here we have an island-effect, in which Zosterops has 'filled in for' the paucity if true nectarivores - particularly Nectariniidae (https://en.wikipedia.org/wiki/Sunbird) - in the avifauna of Mauritius.

https://www.perplexity.ai/search/Are-any-aphids-C5vQp3GrSe.lh2p4rkJcEg

https://www.perplexity.ai/search/Are-Flatopsis-nivea-nQDvKB2KTB..BGtqdj_9eg

Delphacidae occur on Oceanic islands and produce honeydew

to be continued in https://www.inaturalist.org/journal/milewski/95329-a-new-interpretation-of-the-evolutionary-and-ecological-strategy-of-whiteyes-silvereyes-zosterops-part-3-encephalisation-braininess#...

Publicado el junio 2, 2024 05:21 MAÑANA por