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A followup to this question.

In my world, mushroom producing fungi have developed a symbiotic relationship with algae (or cyanobacteria) similar to Prototaxites. These fungi exist alongside all the usual plant species of earth, thriving in niches such as the dimly lit floor of dense rainforests, and as primary 'vegetation' in the month long nights of cool damp polar regions.

They have developed a range of shapes and sizes, from upright broad-headed shields and chanterelles, to spreading clubs and corals, to tree-climbing brackets. They have also developed a varieties of colors based on the color-absorping pigmentation of their algae or cyanobacteria symbiotes. The fungus still retain their hyphae below ground which they use to capture nutrients from the soil, but their above ground mushroom structures are strengthened with chitin and last for years, or even centuries.

Similar to how insects pollinate flowers, and birds and mammals disperse seeds for flowering plants, what animal species are crucial to the ecology of these mushroom forests?

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  • $\begingroup$ Can't fungi pretty much exist on dead plants and animals? $\endgroup$ – Mikey Nov 21 '16 at 20:54
  • $\begingroup$ @Zxyrra I mention the dimly lit floors of rainforests and cool damp polar regions (think the Aleutian Islands, Newfoundland, or Kamchatka). Both characterized by low light and constant moisture. $\endgroup$ – kingledion Nov 21 '16 at 21:41
  • $\begingroup$ Oh right, sorry, missed that. $\endgroup$ – Zxyrra Nov 21 '16 at 21:45
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    $\begingroup$ @James They are asking "On my planet, what animals must I create so that my mushroom forests are sustained" $\endgroup$ – Zxyrra Nov 21 '16 at 22:30
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    $\begingroup$ Obviously: Gnomes!! $\endgroup$ – Grimm The Opiner Nov 22 '16 at 13:47
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Animals are optional for reproduction

While plants may employ animals to transport seeds, pollen, or other bodies carrying genetic material, fungi make use of other methods. These methods may employ animals, but would work perfectly fine without them. Additionally, most fungi are asexual - so there is no need to transfer genetic material with other "trees".

Spores
An equivalent to seeds, they are released in large numbers (sometimes in the trillions!), which increases the chance of survival. Spores are small, and are carried by air, so while contact with animals may spread them, it is really not necessary. Sometimes spores are also carried in a liquid as opposed to the traditional ~dust cloud

Fragmentation
This occurs when part of the mycelium (root equivalent) or thallus (body) of a fungus breaks off unintentionally, then sprouts to form a new individual organism. Natural processes can easily break down your forest, but if you want animal contact, you can consider something that eats your "trees", maybe similar to a beaver - that spreads new organisms through its feces.

Budding
When cells divide off of a fungus for the specific purpose of reproduction (as opposed to tissues breaking unintentionally and sprouting), budding occurs. Animals cannot facilitate or aid in this process.

In summary
These methods will work fine independent of animal interaction, but you may employ animals to consume your "trees" if you wish.


Animals are needed to provide nutrients, but the type may vary

Why not just photosynthesize?
While your forest uses photosynthesis to produce sugar, which is an added boost, even plants use roots to obtain the nutrients they don't get through photosynthesis. Some things must come from other sources.

Why animals instead of other plants?
The problem with having a forest with set, unchanging flora is that the soil quickly loses the nutrients needed for healthy growth. That's why crop rotation is so important; many new nutrients must be introduced in some way. However, in nature, animal populations provide the solution when farmers aren't there to switch out what grows.

How should the forest take nutrients from animals?
The best way to constantly replenish your forest's nutrients is to kill some animals every once in a while. Luckily there are plenty of lifestyles that will allow for this:

  • Carnivorous: Like carnivorous plants, your fungi may lure in animals such as insects and small birds, and break down their bodies to help them grow. There are plenty of ways to lure and trap animals - sweet scents, bright, attractive colors, closing parts, one-way pits, etc. The type of animal lured is not specific.
  • Decomposing: Following traditional fungi, your forest could break down the corpses of (plants and) animals on the forest floor using its mycelium (roots). The type of animal decomposed is not specific. Additionally, feces may be broken down by the hyphae.
  • Parasitic carnivores: You could consider growing your organisms on top of large living creatures. As long as the creatures are around, the forest will be. While this is appealing as it requires minimal work, it puts the "trees" in an evolutionary corner: if the hosts go extinct, so too do they.
  • Parasitic decomposers: Your forest could intentionally kill animals, and break down their bodies. This varies from carnivores because animals are not being attracted actively. An example of this is releasing toxic spores that, when inhaled by living things, kill them, before taking root. Using their nutrients as fuel and building materials, the spores proliferate. The types of animals in these circumstances can vary.
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  • $\begingroup$ Don't forget that animals also poop. $\endgroup$ – Tofystedeth Nov 21 '16 at 22:32
  • $\begingroup$ @Tofystedeth I mentioned that under "fragmentation" but I will add it under "how should the forest take nutrients", thank you $\endgroup$ – Zxyrra Nov 21 '16 at 22:33
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    $\begingroup$ @ThomBlairIII Editing into my answer now, and I hadn't seen that before. Interesting $\endgroup$ – Zxyrra Nov 22 '16 at 4:57
  • $\begingroup$ I think decaying bacteria in the soil could also be considered as potential nutrient source, just in case that wasn't explicitly obvious from your answer. Soil must be teeming with bacteria. $\endgroup$ – Thom Blair III Nov 22 '16 at 12:01
  • $\begingroup$ @ThomBlairIII While bacteria surely do produce some nutrients, they don't seem to have enough of an impact on Earth to negate the need for crop rotation. Still, if the Great Oxygenation Event happened in the soil, with some non-oxygen substance... maybe $\endgroup$ – Zxyrra Nov 22 '16 at 16:48
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Animals Are Rarely Necessary

As stated in previous answers, animals are not needed for most mushroom reproduction.

However Coprophilous fungi only grow on fecal matter:

Coprophilous fungi release their spores to the surrounding vegetation, which is then eaten by herbivores. The spores then remain in the animal as the plants are digested, pass through the animal's intestines and are finally defecated. The fruiting bodies of the fungi then grow from the animal feces.

So this is one case where animals, herbivores, are indeed needed.

Plants and Ecosystems are Most Common Requirements

Perhaps the most important requirement for mushroom growth, though, is their dependancy on certain environments. For example, some mushrooms grow only on birch trees, others only grow on the ground under conifers. Some only grow in shade, others grow in sunny fields. Some require humid, tropical conditions, while others only grow in the desert.

So, although animals are not required generally for mushroom growth, each species usually has very specific environmental requirements.

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    $\begingroup$ Coprophilous fungi are intriguing, thank you. $\endgroup$ – kingledion Nov 22 '16 at 4:55
  • $\begingroup$ "As stated in previous answers, animals are not needed for most mushroom growth" On the contrary, the only other answer stresses the importance of animals for nutrients $\endgroup$ – Zxyrra Nov 22 '16 at 6:27
  • $\begingroup$ @Zxyrra Sorry, yes, I will edit my answer. Regarding necessity of animal nutrients, I agree animals could be an important source of nutrients, but I am not aware of any evidence suggesting animal bodies would be required to provide nutrients plants could not. Certainly the author could choose to make that decision, but in terms of current science, I don't know of any research showing animals alone can provide necessary nutrients. $\endgroup$ – Thom Blair III Nov 22 '16 at 11:56
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While I don't believe this simple answer should dictate anything for your world, from basic observation on land I owned that was rife with mushrooms, I can say that the most common visitor to said mushrooms were mollusks... slugs and snails, which actually fed on some of the mushrooms directly.

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