In the equation GPP−R=NPP R represents :

The correct answer is Respiration losses.

Explanation:
In ecology, the relationship between different types of primary productivity in an ecosystem is represented by the following equation:
$\mathrm{GPP}-R=\mathrm{NPP}$

Let's break down each term of the equation to understand what they represent:
1. GPP (Gross Primary Productivity): This is the total amount of organic matter (chemical energy) produced by plants (primary producers) through photosynthesis per unit area per unit time.
2. R (Respiration losses): Plants consume a portion of the organic matter they produce for their own cellular respiration, metabolic processes, and maintenance. This energy is lost as heat and is denoted by $R$.
3. NPP (Net Primary Productivity): This is the remaining organic matter after accounting for respiration losses. It represents the actual biomass available for consumption by heterotrophs (consumers and decomposers) in the ecosystem.

Therefore, in the equation $\mathrm{GPP}-R=\mathrm{NPP}$, the letter R represents Respiration losses.