Like many other patterns, investment in research is often cyclical. International centers like CIMMYT have focused substantial resources on biotic and abiotic stresses for about two decades now, but raising total productivity is also back on the development agenda. There are a number of reasons for this, among them sharp rises in the price of staple foods as well as the manifestation of detrimental effects of climate change on productivity. Those factors threaten not only the livelihoods of resource-poor people but food security at...
C H A P T E R 1 0
Reproductive (Biotic) Potential
The maximum number of young that a population can produce under ideal conditions during a particular time period is referred to as the reproductive (biotic) potential of that population.
Science is occurring all around you,
and the opening photo of each chapter will preview the
science you will be learning about. The Chapter
Preview will give you an idea of what you will be
learning about, and you can try the Launch Lab to
help get your brain headed in the right direction. The
Foldables exercise is a fun way to keep you organized.
This book is the result of discussions that took place at the Pellston Workshop on
Assessing the Hazard of Metals and Inorganic Metal Substances in Aquatic and
Terrestrial Systems. The workshop, sponsored by the Society of Environmental
Toxicology and Chemistry (SETAC), was held 3–8 May, 2003, in Pensacola, FL.
Chemical reactions (abiotic reactions) are “classical” chemical reactions that
are not mediated by bacteria. They may include reaction processes such as
precipitation, hydrolysis, complexation, elimination, substitution etc. that
transform chemicals to other chemicals and potentially alter their phase/state
(solid, liquid, gas, dissolved).
Precipitation is the removal of ions from solution by the formation of insoluble
compounds, i.e. a solid-phase precipitate.
Hydrolysis is a process of chemical reaction by the addition of water.
The contamination of metals is a major environmental problem and especially in the aquatic
environment. Some metals are potentially toxic or carcinogenic even at very low
concentration and are thus, hazardous to human if they enter the food chain. Metals are
usually dissolved into the aquatic system through natural or anthropogenic sources. Metal
ions are distributed thoroughly during their transport in different compartments of the
aquatic ecosystems, in biotic or abiotic compartment such as fishes, water, sediment, plant.
Reactions and transformations of chemicals. Many chemicals undergo reaction or
transformation in the subsurface environment. In contrast to retardation contaminants may be
removed, rather than simply slowed down. Reactions of harmful chemicals to yield benign
products prior to arrival at a receptor are the ideal, e.g. many toxic hydrocarbons have
potential to biodegrade to simple organic acids (of low health concern and themselves
potentially degradable), carbon dioxide (bicarbonate) and water. Transformation often causes
a deactivation (lowering) of toxicity.