These diagrams explain entrapment in the simplest terms.  They end by indicating some of its complexities. Entrapment is essentially an ecological concept.
 

Figure One. Entrapment starts with  a circumscribed area of land on which a community of people live  - their local ecosystem. Theoretically it  can be any size, from an  individual farmestead to the world as a whole.  In practice it is easiest  to think in terms of countries,  because  the data with which to diagnose entrapment are usually  collected for countries.
 
 
 
 
 
 
 
 
 

Figure Two. All ecosystems are driven by the energy of the sun.  Plants use this energy to grow and make food crops. People eat this stored energy, which is shown here as bananas.   To begin with,  all the food energy  a community needs is produced by its  own ecosystem.

Figure Three. However, as the population increases there comes a point when the community is so large that it exceeds the carrying capacity of its piece of land -  its local ecosystem. There are more people than the land can support.
 
 
 
 
 
 
 
 
 
 
 
 

Figure Four. If a community exceeds the carrying capacity of its  ecosystem, and is fortunate: (i) People  can  migrate to new land. (ii)   They can  make exports,  and exchange them for imports,  especially food. By eating imported food they are making use of light energy that falls on other parts of the world. This can go on until there are more people than the world as a whole can support - until humanity exceeds the global carrying capacity. There are signs  that this may have happened. See.

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Figure Five. For a community to produce exports, it has to have an economy  which can  produce them.  For the rapidly growing communities of Africa,  the problem is to develop the economy fast enough,  to produce the essential imports,  especially food.

Figure Six. What happens if the carrying capacity has been exceeded, there is nowhere to migrate to  and the economy produces too few exports to exchange for the  essential imports, especially food?  This is the condition of demographic entrapment.

                The formal  definition of entrapment is this: A community is demographically trapped if it exceeds the carrying capacity of its ecosystem, and  its ability to migrate, and the ability of its economy to produce the necessary exports which it can exchange for the essential imports especially food. It is also trapped, if because its population is increasing, it is going to be in this unhappy situation before long.
 
 

Figure Seven. The  alternatives then  are starvation or slaughter. People can either stunt and starve, or they can kill one another.
 

Figure Eight. These simplified figures can be progressively refined.  Here is a beginning.

               1. The edges of trapped areas are best thought of as 'gradients' rather than sharp borders.  In Africa political borders are usually  rather nominal. Even so,   any difficulty over migration   indicates that there is a discontinuity between the place being migrated from, and the place being migrated to - in effect a border.

              2. At what scale should entrapment be diagnosed? Should one think of the entrapment of (i) single farmsteads in Rwanda,  (ii) of the Rwanda as a country, (iii) of   Rwanda and Burundi, (iv)  of the Great lakes region of Central Africa, (v) of Africa as a whole, or (vi) of the world?  Answer: One needs to think at all these levels, and to consider the  extent to which communities within them  may or may not be trapped.
 

               3. Entrapment is seldom uniform.   Population pressure is usually denser in some places than in others.

               4. What standard of living ? Food consumption alone varies from 200 kg of grain annually in India to 800 kg in the USA?   For  simplicity  diagnosing entrapment, we consider  merely survival - in effect the 200 kg level.   This is  a necessary beginning. What the 'reasonable' or  'optimal' level  might be is important - and  the subject of much argument.

               5. What about other creatures, especially the animals?    For simplicity the figures  consider only man, and assume that man is the only creature supported by an ecosystem.  There are many aspects of this:

               (i) Animals are inefficient energy converters. When  farm animals   convert  the energy stored in plants into that stored in their own bodies they waste a lot of it.   This is why, if  carrying capacity for humans is to be maximized,  we humans should  eat a diet which is largely grain - a 'photon efficient diet' - one which converts the light energy falling on an ecosystem into food energy with  maximal efficiency.
 

                (ii) The maintenance of biodiversity, both for its own sake, and for its use by man requires that man  be  not the only  creature to be considered, and that the rest of creation should have its share.  Hence the importance of game parks, etc.

               6. What economy?.The simplest economy can produce exports of primary products, particularly minerals, and timber,  and high value agricultural exports, such as cocoa, and tobacco.  But if more than minimal imports are required, they are likely to have to be produced by the export of  manufactures,  and services, such as tourism.

                7.  Is all  slaughter caused by entrapment?  Most certainly not!!  Intense population pressure in a primarily agricultural community, is merely one powerful cause.  Whether a community starves or slaughters itself  is likely to depend on whether there are  powerful social tensions in the community. Systematic genocide of the Rwandan pattern is likely to be  the  exceptional event, and disordered slaughter much more likely.

                8.  What happens to carrying capacity?   Carrying capacity needs to go up to counter entrapment. Unfortunately, it commonly goes down.

Figure Nine.[1] In a tropical forest ecosystem most of the nutrients (nitrogen, potassium, phosphate, etc.)  are in the biomass (vegetation). When this is burnt and crops are planted, the land is initially very fertile, but it steadily falls, as in this figure.  "...Land-mining or soil mining, defined as 'productivity without sustainability' is the norm [our italics]  rather than the exception in the Third World, especially in Africa.  Everywhere, farmers take out from inherently marginal and easily degradable land more than they put back; they mine the land until it is virtually  rendered useless..." [2]

1.   Ministry of Agriculture, Animal Industry and Fisheries, Uganda.  Obtained from the Department of Agriculture, Makere University, Uganda. 1996.

2. Beets WC. Raising and sustaining productivity of smallholder farming systems in the tropics. A Handbook of sustainable Agricultural Development. Agbe Publishing, Box 9125  1800 Alkmaar, Holland.