Productivity (ecology)
In ecology, the term productivity refers to the rate of generation of biomass in an ecosystem, usually expressed in units of mass per volume (unit surface) per unit of time, such as grams per square metre per day (g m−2 d−1). The unit of mass can relate to dry matter or to the mass of generated carbon. The productivity of autotrophs, such as plants, is called primary productivity, while the productivity of heterotrophs, such as animals, is called secondary productivity.[1]
The productivity of an ecosystem is influenced by a wide range of factors, including nutrient availability, temperature, and water availability. Understanding ecological productivity is vital because it provides insights into how ecosystems function and the extent to which they can support life.[2]
Secondary production[edit]
Secondary production is the generation of biomass of heterotrophic (consumer) organisms in a system. This is driven by the transfer of organic material between trophic levels, and represents the quantity of new tissue created through the use of assimilated food. Secondary production is sometimes defined to only include consumption of primary producers by herbivorous consumers[18] (with tertiary production referring to carnivorous consumers),[19] but is more commonly defined to include all biomass generation by heterotrophs.[1]
Organisms responsible for secondary production include animals, protists, fungi and many bacteria.
Secondary production can be estimated through a number of different methods including increment summation, removal summation, the instantaneous growth method and the Allen curve method.[20] The choice between these methods will depend on the assumptions of each and the ecosystem under study. For instance, whether cohorts should be distinguished, whether linear mortality can be assumed and whether population growth is exponential.
Net ecosystem production is defined as the difference between gross primary production (GPP) and ecosystem respiration.[21] The formula to calculate net ecosystem production is NEP = GPP - respiration (by autotrophs) - respiration (by heterotrophs).[22] The key difference between NPP and NEP is that NPP focuses primarily on autotrophic production, whereas NEP incorporates the contributions of other aspects of the ecosystem to the total carbon budget.[23]
Species diversity and productivity relationship[edit]
The connection between plant productivity and biodiversity is a significant topic in ecology, although it has been controversial for decades. Both productivity and species diversity are constricted by other variables such as climate, ecosystem type, and land use intensity.[24] According to some research on the correlation between plant diversity and ecosystem functioning is that productivity increases as species diversity increases.[25] One reasoning for this is that the likelihood of discovering a highly productive species increases as the number of species initially present in an ecosystem increases.[25][26]
Other researchers believe that the relationship between species diversity and productivity is unimodal within an ecosystem.[27] A 1999 study on grassland ecosystems in Europe, for example, found that increasing species diversity initially increased productivity but gradually leveled off at intermediate levels of diversity.[28] More recently, a meta-analysis of 44 studies from various ecosystem types observed that the interaction between diversity and production was unimodal in all but one study.[29]
Human interactions[edit]
Anthropogenic activities (human activities) have impacted the productivity and biomass of several ecosystems. Examples of these activities include habitat modification, freshwater consumption, an increase in nutrients due to fertilizers, and many others.[30] Increased nutrients can stimulate an algal bloom in waterbodies, increasing primary production but making the ecosystem less stable.[31] This would raise secondary production and have a trophic cascade effect across the food chain, ultimately increasing overall ecosystem productivity.[32]