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Chapter 3 Aegism : This book commences its story of plant-animal and animalanimal relationship s i n th e sea s o f Hon g Kon g wit h categories tha t d o no t fi t neatl y int o th e mor e easil y interpreted categorie s o f commensalism , mutualis m an d parasitism tha t ar e t o follow . Indeed , man y moder n definitionists usuall y restric t themselve s t o th e thre e categories above and what will be discussed are incorporated into one or other o f them . But I believe ther e i s anothe r category which is encompassed by the term aegism, itself embracing th e olde r term s o f epizoism , endoecism , inquilinism and phoresis. The commo n threa d linkin g thes e association s i s protection, wit h on e specie s livin g unde r th e aegis o f it s partner, whereas for all other categories, there are usually strong feedin g overtone s t o the relationships. Mutualists , as we shall see , often provid e foo d fo r eac h other , either directly or indirectly; commensals are defined a s 'feedin g at the same table', while parasites obtain their nourishment to the detriment of their hosts. To seek out the thread of protection that links a group of animals, we must begin with the simplest of concepts, that of epizoism, which simply means living atop another. Though this sounds unlikely and we see few examples of it on land , i t i s commo n i n th e se a — especiall y i n thos e coastal environment s tha t are crowded with life. Thus on rocky coasts , barnacles an d mussel s settl e upo n oysters ; tubeworms crow d th e surfac e o f Sargassum frond s an d algae encrust the backs of limpets. Herbivores often live on top o f thei r alga l foo d whil e smal l predator s an d ectoparasites live alongside their prey and host, respectively. Most simple epizoic associations have little or no element of permanence but simply reflect th e intense competitio n for space in a crowded environment. After all, for a barnacle, an oyste r i s a s goo d a substrat e t o liv e o n a s a rock ; Sargassum fronds are unoccupied space for tube-worms to attach t o while th e alga e o n a limpet' s bac k i s th e onl y place on a grazed surface which the limpet cannot reach to for Protectio n crop! Som e herbivore s mov e t o ne w pasture s whe n on e frond ha s been chewe d t o its bas e just a s predators see k new prey when an existing food resource is depleted. For others, however , w e ca n se e som e benefi t fro m livin g together. The limpet, in pastures of algae, is camouflage d by its cover of plants, oysters are hidden by their blanket of barnacles and so long as the weight of encrusting organisms does not interfer e wit h norma l activities , som e benefit i s accrued. But in each case there is little sense of commitment or obligation. Space is a rare commodity and in the search for it, survival is at stake. Such associations, often random, loosely-knit an d withou t an y elemen t o f obligation , d o confer one thing — camouflage, and thus protection. The secon d categor y her e include d unde r aegis m i s endoecism whic h describe s a muc h mor e specifi c partnership where one animal habitually finds shelter with another. Mos t example s o f thi s category o f partnership s relate to those animals which shelter within the burrow of another, but , a s w e shal l see , man y suc h example s ar e better categorized as commensalistic because the commensal is usuall y hos t specifi c an d ther e i s thu s th e elemen t o f commitment or obligation. We can see simple examples of endoecism all around us on the shores of Hong Kong. On sand flats , whe n th e tid e goe s out , rovin g herbivorou s...

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