Critical Thinking Question # 2, Chapter 45.
The age structure diagram on the left appears to be from a developing nation with a rapid
positive growth rate. Individuals are more likely to have many children if they are
needed to help with agriculture and/or women do not have access to effective birth
control. Therefore, the largest group of individuals is composed on pre-reproductive
individuals. The death rate is quite high from birth on which may be the result of poverty
and malnutrition. It also looks as though this population does not have many medical
advances since relatively few live until old age. With this type of rapid growth rate,
density-dependent limitations, such as food and water, may be a great factor in the future.
The age structure diagram on the right shows a very different picture. In this population
there are almost an equal amount of individuals at each age and it represents a zero
growth rate. One could speculate that this is a country that is in some way limiting its
birth rate. This population appears to be from an country with access to good medical
care and education and the current status is probably quite good economically and
socially.
1. After 4 months, the control population appeared to increase by 40%.
[(140-100)/100]*100 = 40%
2. Both treated plots appeared to decrease dramatically to less than 20% of the
original number of ants before treatment.
3. Yes, at one year it appears both treatments were equally successful at controlling
ant numbers.
4. The longer term study indicated that pesticides along were much less successful at
controlling ants and by 28 months, the ants were back ~45% of the original
number of ants. The pesticides and biological control agents appeared to
completely control the ants by 28 months.
Critical Thinking Question #1.
The principle of competitive exclusion best explains the situation when cows are
instilled with an increase of naturally occurring bacteria to discourage the growth
of an undesirable strain. Since both species would inhabit the same niche, it is
reasonable that the well-established species would not allow the other to
effectively colonize the gut. This seems much more desirable that feeding the
cows antibiotic-laced food for several reasons. First the antibiotics may destroy
the natural flora of the cow’s digestive tract along with the harmful strain. This
may make the digestive process in the cows more difficult. Secondly the
consumers of the milk or meat from the cow may ingest small amounts of
antibiotics. Therefore we may be creating an atmosphere for antibiotic resistant
organisms to develop in the consumer.