Global Change Ecology (BIO347)

Food for a growing population of humans

Today we have a large population of people who are starving or suffering from malnutrition. According to the food assistance branch of the UN, the World Food Program, 45% of deaths in children under the age of five is caused by poor nutrition. They also state that in the sub-Saharan Africa, which is the region with the highest prevalence of hunger, one in four people are undernourished

As we can see getting enough food for our large human population is already a problem – and it is only going to get worse.  The human population is predicted to keep growing up to 9 billion (Godfray et al. 2010).

To understand some of the problems with choosing types of food for a larger human population we need to know a little bit about different trophic levels, which ScienceDaily defines as:

“In ecology, the trophic level is the position that an organism occupies in a food chain – what it eats, and what eats it.”ScienceDaily 11/02/16

In each trophic level the organism is using most of the energy for everyday processes, and that energy is ultimately lost for the ecosystem as respiratory heat. The energy that is not lost is used to build new biomass, which is called the production efficiency. Across all species the average production efficiency is 10 %, which means that the remaining 90 % is lost between each trophic level. These numbers differ between types of organism and especially with what kind of metabolism the organism has. The production efficiency can be anything from 1% to 50%.

Let’s look at one example. 10 % of the energy that the grasses produce during a lifetime is possible to transfer to the next trophic level: a cricket. The growth of the cricket biomass, which is only 10 % of the energy it got from the grass, will be the source of energy for a rodent. 10 % of that energy again will be accumulated in the biomass of the rodent, which the owl will be eating. So if you start out with 1000 kcal of grass, the owl at the top will only end up with 1 kcal of this.

This helps us to understand that if we use a lower trophic level as a source for food, we can get more food for more people and less energy is lost in the food chain.

By simulating the scenario that we eat less meat Stehfest et al. (2009) have found that we could reduce the amount of pasture area with 80 % compared to our dietary habits of today. This means that we could produce more food for more people, but decrease our use of land for food production. Stehfest et al. (2009) also points out that this could have a positive effect on the climate because these former crop-landscapes would capture carbon from the atmosphere as the vegetation grow back.

It looks like one of the ways that we can solve the problem of finding enough food for a growing human population is to reduce our consumption of meat. Are we willing to do that?

Written by: Ragnhild Gya

 

Sources:

Begon M., R.W. Howarth, C. R. Twonsend. (2014). The flux of energy and matter through
ecosystems. In: Essentials of Ecology. United States of America: Wiley. p 309-340.

Godfray H.C.J., J. R. Beddington, I.R. Crute, L. Haddad, D. Lawrence, J.F. Muir, J. Pretty, S.
Robinson, S. M. Thomas, C. Toulmin (2010) “Food: Security: The Challenge of
Feeding 9 Billion People”. Science. 327: 812-818

ScienceDaily. (2015). Trophic level. Available:
http://www.sciencedaily.com/terms/trophic_level.htm. Last accessed 11/02/16.

Stehfest E., L. Bouwman, D.P. van Vurren, M.G.J. den Elzen, B. Eickhout, P.Kabat (2009)
“Climate benefits of changing diet”. Climatic Change. 95:83-102

World Food Program. (2016). Hunger Statistics. Available: https://www.wfp.org/hunger/stats.
Last accessed 11/02/16.