I apologise profusely for asking a silly question, but I am feeling confused and I am seeking more clarity on this subject.

Could anyone, please help me understand why the interaction between climate change, habitat loss, and monotonous diets with the energetic suppression of the bee itself (shown in diagram 1) has a positive (+) symbol?

Would these factors not have a negative effect (-) on the bees energetic suppression?

Would you only add + or - symbols to define interactions when:-

  1. Two biotic factors (i.e. foxes predating on rabbits);

  2. One biotic and one abiotic factor (i.e. the effects of elevated temperatures on bee population abundance);

Would you not add + or - symbols for two abiotic factors i.e. elevated temperature produces extreme weather events and negatively affects a species habitat as these interactions don't involve living organisms (as shown in diagram 2)?

If anyone can help me understand better, I would be deeply appreciative!

Diagram 1

Diagram 1 provides an overview of how parasites, pathogens and pesticides as well as other stressors interact to affect honey-bee health, eventually causing CCD in honey-bees.

How do insecticides and pathogens act synergistically to affect honey-bee health?

There are several hypotheses that have been proposed to explain the effects of pesticides (insecticides and fungicides) and pathogens on bee mortality and CCD including:

Exposure to insecticides suppresses the immune response of bees, promoting pathogenic parasitic (Nosema) infection and as a consequence increased viral loads. The mechanism by which immune suppression occurs has recently been elucidated (see Optional material). Nosema infection induces energetic stress in honey-bees that results in higher food intake by infected individuals. This directly results in an increase in insecticide oral exposure, increased toxicity and higher mortality in infected individuals. Bees are commonly exposed to plant compounds that can be toxic (called phytochemicals, e.g. nicotine) and use enzymes (P450 enzymes) to detoxify these compounds and also insecticides. When exposed to fungicides, these enzymes are inhibited, increasing the toxicity of insecticides to bees and also making them more susceptible to Nosema infection. Honey-bees have a form of social immunity (which is found in many social insects) that consists of cooperation between individual group members to prevent disease contamination. This collective immune defence includes hygienic behaviour where diseased individuals in the brood are removed from the hive, as well as the secretion of antiseptics to sterilise brood food. Exposure of bees to a combination of pathogens (Nosema) and neonicotinoids compromises their ability to sterilise larval food by decreasing the activity of an enzyme known as glucose oxidase. This enzyme catalysis the oxidation of beta-D-glucose to D-gluconic acid and hydrogen peroxide, the latter having antiseptic properties. A decrease in hydrogen peroxide allows the pathogens to spread within colonies.

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Diagram 2

Currently, the main stressors on bee populations are considered to be agrochemicals, parasites and poor (monotonous) diets. The interactions between these stressors can also increase the stress on bee populations. However, the Goulson paper also briefly discusses how climate change may become an increasing stress on bee populations in the future, and mentions a couple of impacts of climate change that may negatively affect bee populations. In Session 3.3.11, you also learned how ecosystem function can be impacted by climate change through different processes.

Drawing on the information of climate change in bee populations and the knowledge of ecosystem processes, draw a systems diagram that illustrates the potential impact of climate change on bee populations. This diagram should include impacts of climate change that can affect bee populations directly as well as indirectly (i.e. via impacts on other bee stressors). Your diagram should, therefore, show the cascading effects of climate change, acting both directly and through specific stressors, on bee populations.

enter image description here

  • $\begingroup$ Can you link the original source of this diagram? +/- is usually used to denote positive/negative interactions, respectively. Some people also use arrowhead for positive interaction and a "tee" (⊣) end for a negative interaction. So there is no universal standard. In your case it looks weird. For instance, P450 system should reduce toxicity but in the diagram the interaction is depicted with a +. $\endgroup$ – WYSIWYG Apr 3 '19 at 10:00
  • $\begingroup$ Hi WYSIWYG. The first diagram was taken from an example supplied from the Open University. I supplied the relevant information that accompanied the diagram. The second diagram, I drew myself to answer the question. I placed as much information as possible so my question might make more sense now. I hope this is what you need to provide insight. Many thanks for your help! $\endgroup$ – Alice Hobbs Apr 3 '19 at 13:46
  • $\begingroup$ The original diagram is inconsistent with the use of symbols. As I mentioned, P450 should have a negative effect on toxicity but it is indicated by a +. The interaction between deformed wing virus and mortality (which is a positively correlated interaction) is also denoted by a +. Now, again, immune response also has a + interaction on the virus. Overall, this diagram is inconsistent with the usage of the symbols and is hence wrong. $\endgroup$ – WYSIWYG Apr 4 '19 at 11:29
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    $\begingroup$ I'm voting to close this question as off-topic because it is based on a non-standard and incorrect premise that is not even a part of a published text. $\endgroup$ – WYSIWYG Apr 4 '19 at 11:30
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    $\begingroup$ I understand. But the most common usage is that + denotes a positive effect (causal) on the on the node where the edge is directed to (conversely for -). However, I cannot be sure about this diagram because it doesn't really rationalize these interactions. For example, I would expect immune response to suppress the virus and P450 system to reduce toxicity. Both these interactions should have a - but they have a +. The premise is, hence, unclear. By published text, I mean something published in a book or a peer-reviewed article (at least a place that has figure legends). $\endgroup$ – WYSIWYG Apr 4 '19 at 14:00

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