Age and area; a study in geographical distribution and origin of species . EndemicsWides -100 - 200 -300 - 400 - 500 - 600 - 700 -800 - 900 -1000 -1080 Malaya, probably indicating an invasion thence, the southerngroup belongs to Ranunculaceae, Umbelliferae, and otherfamilies prominent in the northern hemisphere (the only ex-ceptions being Stylidiaceae and Centrolepidaceae, both southernfamilies), and the central group to Stackhousiaceae, Campanu-laceae, Violaceae, etc., which may perhaps have come fromAustralia. If now one add together all the species of the genera of thenorthern invasion that
Age and area; a study in geographical distribution and origin of species . EndemicsWides -100 - 200 -300 - 400 - 500 - 600 - 700 -800 - 900 -1000 -1080 Malaya, probably indicating an invasion thence, the southerngroup belongs to Ranunculaceae, Umbelliferae, and otherfamilies prominent in the northern hemisphere (the only ex-ceptions being Stylidiaceae and Centrolepidaceae, both southernfamilies), and the central group to Stackhousiaceae, Campanu-laceae, Violaceae, etc., which may perhaps have come fromAustralia. If now one add together all the species of the genera of thenorthern invasion that occur at each zone of 100 miles fromnorth to south in New Zealand (including Stewart Island), oneobtains the curves shown above, from which one may perhapsinfer that the invasion was at about 0-300 miles from NorthCape. The two curves fall off very steadily towards the south, 80 AGE AND AREA [pt. i but that for endemics much more rapidly than that for wides,the maximum in each case being at about the same spot, and. 10 -100 - 200 -300 - 400 - 500 -600 - 700 - 800 - 900 -1000 -1080 CH. VIIl] INVASIONS 81 the minimum at the same. The more rapid fall of the endemiccurve is to be attributed (on the hypothesis of Age and Area)to the fact that they are in general younger, and so have nothad time to spread so far. Treating the southern invasion in the same way, one obtainsthe curves on p. 80, showing both endemics and wides fallingoff towards the north. The latter are shown with a double curve;the upper shows the grand total of wides, but many begin atthe north and do not occur in the far south, showing that theyprobably really belong to the northern invasion. Subtractingthese gives the lower curve, and the diminishing distance be-tween these two curves shows the way in which these speciesdiminish southwards. The endemics, being more numerous, aresplit into two curves, one endemic to New Zealand only, oneendemic to New Zealand and the outlying islands (Kermadecs,Chathams, Aucklands).
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