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CAUSES OF ORGANISM LOSSES

All species will eventually disappear, upon replacement by new creatures having better adaptations to changing environments.  Although a natural process, it is not uniform; organism declines tend to occur in clusters through both time and space.  

My own scheme for grouping specific causes of endangerment and extinction (a scheme that has NO formal recognition) consists of four classes:

• natural declines

• over-exploitation by humans

• habitat modification by humans

• human introduction of foreign organisms

Be aware of two qualifying remarks, however.  

• With new information constantly becoming available, and yet still a multitude of unknown cases or inadequate documentation, This is not an exhaustive inventory of declines and losses.

• Usually there is a synergism of multiple contributing factors from several cause classes that lead to endangerment; the scheme I present here is a vast oversimplification showing my own opinion of the predominant cause class for each example creature.     [BACK]

Natural declines are due to causes and conditions over which humans have little or no influence.  These are creatures, often of ancient lineage, that probably would be disappearing even if humans (and their impacts) did not exist; these creatures have simply reached the end of their time.

Over-exploitation includes organisms that either have suffered direct depredations by humans for purposes of food, pest control, propagule or adult specimen collecting, ornamental use, or deliberate hybridization.

Habitat modification causing declines results from such human practices as toxic contamination, devegetation, prey removal, climate (atmospheric or aquatic) alteration, sedimentation, hydraulic changes, or construction.

Introduction is a subset of habitat modification that warrants attention as a separate class, in that foreign organisms have capacity for permanent propagation of themselves and thereby pose perpetual competitive or predatory threats to indigenous creatures.       

See also the bird, mammal and the following lists: