Download Ecology Drives the Worldwide Distribution of

Richard Ethington
Thursday 1 pm
Biology 1615
Ecology Drives the Worldwide Distribution of Human Diseases
Introduction
Biological diversity on the earth is greatest near the equator. The equator is at zero degrees
latitude. Generally speaking, the further from the equator or the higher degree latitude on the
world, there lower the number of animal and plant species that exist. This pattern is referred
to as the latitudinal species diversity gradient. There are many theories to explain this.
Foremost of the theories are three: area, energy, and time.
Based on the curvature of the earth there is more land area at lower latitudes then at higher
latitudes. The greater surface area could account for the existence of more species. The lower
latitudes receive more energy from the sun than areas at higher latitudes. The region between
the Tropic of Cancer and Tropic of Capricorn is the extent of where the sun is directly overhead
at noon every day of the year. The added heat makes the lower latitudes for a more inviting
animal habitat. The additional direct sunlight (versus higher latitudes) leads to more captured
energy, which can be used in photosynthesis to promote plant life. The sun also is out longer
during the day in tropical climates then higher latitudes. This extra sun light time also would
foster animal and plant growth.
The problem with past explorations of the latitudinal species diversity gradient is that they
were lacking in regard to a major component of life forms. They mostly focused on easier to
track life forms of plants and animals. A large portion of life forms are significantly smaller and
less well tracked. Parasitic and Infectious disease (PID) species were mostly ignored in past
studies. The question this study wished to answer is whether PID’s follow the same latitudinal
species diversity gradient of larger life forms or not. Does the gradient follow ecological
patterns or human patterns?
Materials and methods
Data was collected on 332 different PIDs, including bacteria, viruses, fungi, protozoa,
and helminths from the Global Infectious Disease and Epidemiology database (cyinfo.com).
This data was collected from 224 different countries which span both the southern and
northern hemispheres. 103 of the pathogens were eliminated from the project because of
unavailable vales leaving 229 pathogens to test. The collected data was compared against six
selected human variables of (1) human population totals, (2) human population density, (3)
human birth rate, (4) human death rate, (5) human population growth rate and (6) an economic
factor: the gross national product.
Six environmental factors were also examined. They were (1) continent, (2) hemisphere, (3)
insular country or continental, (4) percentages of arable land vs permanent pastures vs
permanent crops vs irrigated lands vs forest woodland and other, (5) mean latitude, and (6)
mean longitude.
Statistics analysis was performed and arrayed to show comparisons between the twelve tested
factors. The higher the correlation between the PID’s and the twelve tested factors the more
likely the correlations reflected and cause and effect relationship.
Results
The results showed that latitude was the greatest predictor factor tested. Seven out of ten
pathogens were harbored in greater extent along the latitude species diversity gradient. No
differences were noticed between the hemispheres or for the human components tested.
Discussion
PID species make up the majority of life forms on the earth. Their biodiversity totals deserved
to be including in the analysis of the latitudinal species diversity gradient. When considering
the results, we see that total species diversity is much higher than previously recognized.
The results show that PID diversity generally followed the same distribution pattern as those of
larger free living species. PID species require hosts to survive so ecologic areas better suited for
host species will make more suitable areas for PIDs. Also a high correlation exists between
precipitation and lower latitudes. Many PIDs require water or humidity levels to complete their
life spans making lower latitudes more suitable for them.
Microorganisms follow the latitudinal species diversity gradient, this shows that ecological
factors are far more prevalent in PIDs distribution than human factors. This raises alarms to
effects of climate changes on PIDs distribution.
Conclusion
Climate factors are the likely predictor of PID species. The climate factors that foster PIDs
closely coincide with lower latitudes. Latitude itself is certainly no concern for PID’s, but
latitude serves as a proxy variable for environmental factors like temperature, sunlight, and
humidity. The largest climate factor responsible for the biodiversity is energy. Direct sunlight
carries more energy than less direct sunlight received at higher latitudes. Additionally the sun
is up longer during the day at lower latitudes than at higher latitudes. Lower latitudes also
coincide with higher precipitation totals and humidity that many species need to survive. These
factors combine to support free living species exist at lower latitudes as well as PID species.