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11.1: Primary Productivity - Geosciences

11.1: Primary Productivity - Geosciences


The oceans make up the largest habitat on the planet, stretching over approximately 71% of the Earth’s surface and it contains 97% of the Earth’s water. This latter example illustrates the clear connection between the biological processes of autotrophs and heterotrophs through food webs.

Primary productivity is the process where inorganic substances are synthesized by organisms to produce simple organic materials. Primary producers, or autotrophs, are responsible for this phenomenon. Common examples of primary producers include diatoms, dinoflagellates, and coccolithophores. Primary producers can either be photoautotrophs, organisms that synthesize organic compounds using the sun as a source of energy, or chemoautotrophs, organisms that synthesize organic compounds from inorganic molecules found in the environment. Both photosynthesis and chemosynthesis contribute to the oceans’ primary productivity, but photosynthesis is the dominant process with respect to the amount of carbon fixed and energy stored in organic compounds. Photosynthesis is used by autotrophs at the sea surface and high in the water column where light is abundant. Contrastly, chemosynthesis usually occurs in deeper water where little to no light is present.

There is a multitude of factors that determine the effectiveness of primary productivity. While the amount of water, carbon dioxide, inorganic nutrients, and sunlight all play a major role in how productivity, not all of these components act as limiting factors. Neither water or carbon dioxide act as limiting factors in the ocean, as they are abundantly available in the environment. For photoautotrophs, one of the greatest limiting factors is sunlight and light penetration into water columns. Consequently, most photoautotrophs are found near the ocean’s surface (a zone aptly named “the photic zone”) and few are found in the mixing zones at lower depths. Additionally, nutrients such as inorganic nitrogen, phosphorus, iron and/or silica are limiting on living organisms due to their scarcity in the ocean.

Primary production is the most basic building block for energy and the basis for food webs in all environments and ecosystems. In the ocean, autotrophs which are responsible for primary production consist of phytoplankton, marine plants, and macroalgae since they all perform photosynthesis. All photoautotrophs capture solar energy by utilizing the pigmentation such as Chlorophyll A, a pigment that is especially effective in capturing light energy in the blue and red wavelengths of light. There are various pigments used by the many different photoautotrophs in the ocean.

Primary production is often referred to in two ways: gross and net primary production. The entirety of the organic compounds produced by the primary producers is referred to as gross primary production. As with everything it is impossible to have 100% efficiency, the autotrophs require a part of the organic compounds that they produce for their own respiration processes. Net primary production is the measure of the organic matter that is produced by the autotrophs and available for consumption of the heterotrophs.


11.1: Primary Productivity - Geosciences

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System Element Changes

One of the key changes in system elements is the requirement for Food Safety Culture has been updated (2.1.1.2).

This is something that should bring a closer alignment between the SQF and BRCGS Food Safety Issue 8 and follows an emphasis on Food Safety Culture from the FDA in its New Era Blueprint.

A requirement for Food Safety Culture should bring closer alignment between the SQF and BRCGS

That said, what is required here is not necessarily anything new as it has been compulsory in other elements in past versions, e.g., adequate resources being available to ensure objectives can be met is in the requirement for senior management commitment.

Similarly, what is expected and required from the senior manager commitment section seems to be comparable to the expectations in the food safety culture requirement and quality policies should be updated to include food safety culture.

Internal labs that conduct food safety testing must ensure that sampling and testing methods are in accordance with the applicable requirements of ISO/IEC 17025 and there is an annual proficiency testing conducted for staff who perform the analysis work.

This caveat is only required for those conducting food safety testing and not quality testing such as Brix, and the internal lab doesn’t need to be accredited to ISO/IEC 17025.


11.1: Primary Productivity - Geosciences

All articles published by MDPI are made immediately available worldwide under an open access license. No special permission is required to reuse all or part of the article published by MDPI, including figures and tables. For articles published under an open access Creative Common CC BY license, any part of the article may be reused without permission provided that the original article is clearly cited.

Feature Papers represent the most advanced research with significant potential for high impact in the field. Feature Papers are submitted upon individual invitation or recommendation by the scientific editors and undergo peer review prior to publication.

The Feature Paper can be either an original research article, a substantial novel research study that often involves several techniques or approaches, or a comprehensive review paper with concise and precise updates on the latest progress in the field that systematically reviews the most exciting advances in scientific literature. This type of paper provides an outlook on future directions of research or possible applications.

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to authors, or important in this field. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.


Ecological drivers of hunter-gatherer abundance

Although ecological approaches in anthropology and archaeology have a history as long as these disciplines themselves, little is known about the influence of environmental conditions on the abundance of pre-industrial humans. Our new study reveals that net primary productivity, biodiversity, and pathogens have strongly influenced the global pattern of population densities of ethnographically documented hunter-gatherers.

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Our paper “Productivity, biodiversity, and pathogens influence the global hunter-gatherer population density” in PNAS is here: https://doi.org/10.1073/pnas.1715638115

The background story of our paper is pretty boring. It involves neither data collection in exotic places nor careful experiments in the laboratory. However, it is a good example of what can come out as a result of interdisciplinary collaboration. The mixture of backgrounds of an archaeologist (me), an ecologist (Miska Luoto), and a palaentologist (Jussi Eronen) enabled us to analyse old data with fresh ideas and new perspectives – although, eventually, we had to admit that even our fresh ideas were not completely new.

Few years ago, our group in Helsinki started to develop species distribution modelling of population dynamics of prehistoric human hunter-gatherers as a complement to more established archaeological and genetic methods. The idea is to use the information about how environment influences hunter-gatherer population density in modern or historical ethnographic data to hind-cast prehistoric population densities. Such hind-casting requires information about past environmental conditions, which is usually derived from climate model simulations.

In our pioneer study about human population dynamics in Europe over the Last Glacial Maximum, we modelled hunter-gatherer population range and density using potential evapotranspiration, water balance and mean temperature of the coldest month. We took these three variables pretty much as given, because they are ecologically sound predictors of population density in the cold and dry Ice Age conditions. However, we did not explore any alternatives.

After the first paper, it was clear to me that we needed to dig deeper into global-scale hunter-gatherer population ecology. The resulting knowledge would not only make the simulations of prehistoric dynamics more robust, but it would be extremely interesting in itself: Hunter-gatherers, and pre-industrial human populations in general, provide a rare opportunity to investigate the drivers of the distribution and abundance of a single species along global environmental gradients.

Previous studies have shown that primary productivity and other measures of resource abundance have influenced hunter-gatherer density. However, we assumed that not only the total amount of available energy, but also the diversity of potential resources may play an important role by stabilising hunter-gatherers’ subsistence variability. Thus, and given the hypothesised role of species richness in stabilising ecosystem productivity in general (diversity-stability hypothesis), we wanted to explore the effect of biodiversity as well.

Relationship between hunter-gatherer population density and net primary productivity.

Maybe the most intriguing feature in the response of hunter-gatherer population density to environmental variability is the peaking of density in temperate and subtropical climates, where net primary productivity is around 1,400 g/m 2 /year, and the subsequent decline and levelling-off of density when productivity increases above 1,500 g/m 2 /year. We would have assumed that population density shows a monotonic positive response to resource availability. Instead, some factors appear to counter this positive response in high-productivity environments and we were fascinated by our idea that pathogens would cause the observed pattern.

The results appeared to confirm our hunch about the role of pathogens: Pathogen stress was the strongest predictor in the high-productivity environments. Our results also showed that productivity had significant positive effect on hunter-gatherer population density throughout its gradient when the effect of pathogens was held constant – something, which we had assumed, but wasn’t evident in the bivariate relationship between productivity and population density. What we didn’t anticipate was threshold effects. Biodiversity turned out to be the strongest predictor in the low productivity environments of arctic, boreal and temperate biomes, but non-significant in high-productivity of tropics, whereas pathogens showed the opposing pattern. It took the expertise of the two ecologists in our team to acknowledge that the observed pattern resembled the pattern in the factors affecting global biodiversity: Resource availability is important in the high- and mid-latitudes whereas biotic interactions become more dominant in the tropics. It is tempting to speculate that these similarities in the patterns of limiting factors of a single species’ abundance and the global biodiversity might suggest similarities in the underlying mechanisms as well.

Net primary productivity, biodiversity, and pathogens constrain the global hunter-gatherer population density, but their effects vary in different parts of the globe. Biodiversity affects population density mostly in the low-productivity environments, whereas pathogen stress is a crucial constraint on population density especially in the tropics. Blue, red, and grey arrows indicate positive, negative and statistically insignificant effect of a variable, respectively. Thickness of an arrow indicate the strength of the effect of a variable.

When we were making final tuning of our manuscript, we wanted to highlight the result that temperate and subtropical biomes appeared to provide the most suitable conditions for hunter-gatherers due to the optimum between the positive effects of resource availability and the negative effects of pathogens. Knowing that eminent anthropologist Lewis Binford had previously observed that temperate and subtropical biomes provide optimal conditions for hunter-gatherers, I went back to his writings 1 to find out, if he had suggested any mechanism for this optimum. Surprisingly, I found out Binford proposing that resource availability and pathogens would play an important role in driving hunter-gatherer abundance! I was a little confused – our idea was not as novel as we had thought. Luckily for us, however, Binford hadn’t quantified these relationships. It was only a proposition – an idea that we had now corroborated with data. Most likely, I had read Binford’s proposition about the interplay of resources and pathogens years ago, forgot where that idea came from, and started to think that it was our own development. This was a good reminder that novel ideas in science are rarely completely new.


Fundamentals

Tip Sheet 1 – Getting Started
Tip Sheet 2 – Choosing the right SQF Certification
Tip Sheet 3 – Preventing Food Safety Risks
Tip Sheet 4 – Management Commitment
Tip Sheet 5 – The Site Audit
Tip Sheet 6 – HACCP Overview
Tip Sheet 7 – Approved Supplier Program
Tip Sheet 8 – Specifications
Tip Sheet 9 – Document Control and Records Management
Tip Sheet 10 – Legislation
Tip Sheet 11 – Correction, Corrective Action, and Preventative Action
Tip Sheet 12 – Conducting a Risk Assessment
Tip Sheet 13 – Employee Training Program
Tip Sheet 14 – Food Defense Plan
Tip Sheet 15 – Product Identification, Traceability, Withdrawal and Recall
Tip Sheet 16 – Verification and Validation
Tip Sheet 17 – Allergen Management
Tip Sheet 18 – Internal Audit Plan
Tip Sheet 19 – Environmental Monitoring
Tip Sheet 20 – Crisis Management
Tip Sheet 21 – Pest Prevention
Tip Sheet 22 – Personal Hygiene Plan
Tip Sheet 23 – Housekeeping
Tip Sheet 24 – Cleaning
Tip Sheet 25 – Equipment Selection and Maintenance


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