POSITION OF ECOLOGY IN MODERN SCIENCE 189 



which they are subjected. This last point of view is that of ecological 

 phylogeny, or the study of the variability of species during the 

 struggle for space under the direct influence of newly acquired 

 qualities. 



The accumulated data concerning isolated, endemic species and 

 the nearly related forms of a large specific group distributed over an 

 extensive area, are only seen in their true light when we observe the 

 ecological requirements in connection with distinguishing systematic 

 characteristics and also take into consideration the results of recent 

 research concerning the variability of species. Thus we may study 

 from an ecological standpoint the problem suggested by Jaccard as to 

 the cause of the reduction in number of species inhabiting a limited 

 area, the number of genera being correspondingly large. This fact has 

 long been noticed on islands in mid-ocean, and comparison has shown 

 it to be equally true for separate mountain ranges. It appears as if a 

 natural genus, rich in species, were permeated by certain fundamental 

 ecological qualities, which enable it to appear in many places as 

 victor in the struggle for space, yet each species of this same genus 

 can only appear in a few places, so that an association may consist of 

 many different genera, but each genus will be represented by only a 

 few species. This appears to be the solution of the problem concern- 

 ing the development of representative species in widely separated 

 districts whose floral elements appear to have had the same ancestry. 

 This is shown by a comparison of the European, North American, 

 and East Asiatic floras, where we so often find nearly related species 

 filling a similar ecological role. The larch belonging to all three 

 continents, many moorland shrubs, the beech and the birch, all 

 having a wide distribution, can be cited as affording excellent exam- 

 ples of this fact. Sorbus Americana in the mountain regions of New 

 England and New York holds a position similar to that of Sorbus 

 aucuparia of central Europe. Few species have remained exactly 

 the same; the greater number have been broken up into representa- 

 tive forms, showing on the one hand species with decidedly similar 

 ecological adaptation, while on the other hand many species have 

 developed into dissimilar forms possessing dissimilar modes of life. 



The persistence of certain ecological habits in a species, genus, or 

 family, is made the basis of paleontological conclusions. We judge 

 of the climate of central Europe during the Miocene epoch by the 

 conditions existing to-day in places where we find Taxodium, Sequoia, 

 Sassafras, Magnolia, and Platanus. The beeches and firs of that time, 

 we consider, were relegated to the mountainous districts. It seems to 

 us hardly probable that a plant like Taxodium, which in the warm 

 Miocene reached as far north as Spitzbergen and Greenland, and has 

 remained unchanged inform for one hundred thousand years, should 

 alter its climatic requirements; we feel rather that it persists to-day 



