96 



ECOLOGY 



Part II 



anther 



Yucca flower natural size 



Sickle shaped jaw, 

 a pollen collector 



Moth gathering pollen 

 from anther 



Yucca lily 



MOTH AND LILY, MUTUAL BENEFACTORS 



Fig. 6.5. Mutualism, a partnership that benefits each member. The yucca lily, 

 Yucca filamentosa, whose stalks of white flowers grow four to six feet high in the 

 eastern and much higher in the western United States. When the female moth 

 visits a flower she thrusts her long ovipositor into the ovary and deposits an egg 

 beside each of the several ovules (eggs). Then she climbs to the tip of the pistil 

 and carrying pollen that she has collected from some other flower she pushes it 

 into the stalk incidentally making it possible for the transported male cells to 

 fertilize the ovules of the flower she is visiting. After fertilization the ovules 

 develop into seeds; some of them are eaten by the larvae of the moth but others 

 that are untouched propagate the plant. 



hold their places, often against pressure, lack of oxygen, and the defenses of 

 their host. If parasites of digestive tracts did not have a protective immunity 

 to digestive fluids they themselves would be digested. Parasites must reproduce 

 and be distributed in such a way that the young ones can enter into new hosts 

 of the right type and at the right time. Trichinae, the minute worms resting in 

 the pig's muscle, must arrive still alive in a human stomach by way of a sand- 

 wich or a sausage. It is a great gamble, but not a rare feat for trichinae in the 

 United States (Fig. 6.7 and 26.5). 



Development of a Food Habit. Parasitism is primarily a food habit and 

 parasites are mainly chronic predators. Typical free-living predators are larger 

 than their prey, kill it quickly, and devour it soon. A cat pounces upon a 

 mouse, and if hungry, kills and eats it at once. Cats, foxes, and hawks are 



