Editing Eastern Prickly Pear (section)

=== How did it get there? ===

'''What accounts for the ability of a colony of ''O. humifusa'' to exist as far as 20 miles from the nearest neighboring colony?  How did the cactus make such a huge leap without any intermediate colonies?'''  

Granted, this questions seems rather simple.  But, the fact of the matter is that surprisingly minimal research has been invested in answering this question.  Furthermore, the answer is exceptionally important in understanding the fragmented and sometimes boggling distribution of ''O. humifusa'' in Connecticut.

Before I begin, I'll briefly clarify that there are only two basic ways that ''O. humifusa'' can produce independent off-spring.  The first is vegetative, meaning that whenever a cladode becomes detached from the parent plant and hits the ground, it stands a fair chance of sinking its own roots and becoming an independent plant.  The second method is by seed.  The fruits, or "pears", of ''O. humifusa'' contain seeds and wherever the fruits go, the seeds accompany.

First off, we know that the wind is not strong enough to carry a detached cladode or fruit more than perhaps a foot or two from the parent plant.  Under extremely windy conditions, with the right topography, perhaps the wind could move plant pieces even further; I'll say a maximum of 10 to 15 feet, though that would truly exceptional.  This mechanical force may be sufficient to push a detached cladode or fruit over a nearby cliff, at which point it might land on a rocky terrace and begin a new colony.  But certainly, the wind cannot carry a cladode for any significant distance across a landscape.  So, we can say with certainty that ''O. humifusa'' does not disperse long distances of its own ingenuity, in the sense that a dandelion can potentially fly its kite-like seeds for several miles.

Second, I have frequently observed droppings amongst ''O. humifusa'' colonies which appear to be from small mammals, most likely rabbits.  And, indeed, studies in Kansas in the 1940s revealed that rabbits were known to feed upon both the fruits and cladodes of ''O. humifusa''<ref name="kansas">Riegel, Andrew. "Some Coactions of Rabbits and Rodents with Cactus." ''Transactions of the Kansas Academy of Science''. 44. (1941): 96-103. Print. <http://www.jstor.org/stable/3624871>.</ref>.  However, the study observed that rabbits tended to limit their consumption of the cactus to those times when food was particularly scarce, when perhaps the hardy, evergreen ''O. humifusa'' might be the only green plant matter available.  Furthermore, I cannot say that I have noticed any extensive evidence that Connecticut ''O. humifusa'' are subject to consumption by small mammals.  In most cases, the cladodes of ''O. humifusa'' that I've observed are in remarkably pristine condition.  Even if we were to entertain that at some point in the past there was a serious enough food shortage in Connecticut for cottontail rabbits to begin gnawing on ''O. humifusa'' plants, the potential for dispersal by this method is not exceptionally great.  Rabbits aren't likely to detach cladodes and haul them any significant distance, and even if they did, it is further unlikely that they would lose interest in it before consuming enough to kill the vegetative potential of the broken stem.  But then there is the possibility that the seeds of the ''O. humifusa'' pears, after being consumed, might pass through the digestive system of rabbits and be deposited elsewhere.  This is a plausible means of dispersal to which I am open, but it still cannot explain how ''O. humifusa'' might travel a distance of several miles over rough terrain.  The home range of any rabbit is typically restricted to a relatively small area, and no species living in Connecticut are known to migrate long distances.

The most promising theory is that ''O. humifusa'' is distributed long distances chiefly by birds.  Birds have long been observed to consume the pears of ''O. humifusa'' and other species of ''Opuntia'' found elsewhere in the world.  In fact, studies have shown that seeds which first pass through the digestive system of an animal will germinate more reliably and more quickly than those that simply fall from the cactus in an unscathed pear<ref name="us-forest-service"></ref>.  Since birds can potentially travel enormous distances over terrain that would be challenging for terrestrial animals, as well as deposit their droppings from the air in relatively random locations, it becomes clear that birds must have played a decisive role in distributing ''O. humifusa'' across Connecticut.

When we add birds to the equation, there ceases to be any mystery behind how ''O. humifusa'' might have appeared on a high ledge along a ridge or in an isolated glade deep within the forest.  While all of these locations seem like relatively inaccessible locations to man and other mammals, they are simply another place for traveling birds to land or "lighten the load", so to speak, while flying high above.