Hello Janne; Day length isn't the only recurrent pattern that organisms might cue on. The onset of the dry or wet season immediately comes to mind. You might want to include these, and other, cues in your search.

In the parts of the tropics that I know, many insects and amphibians emerge to breed with the first rain of the season. It creates a riot of activity and could easily be related to multiyear trends. Best regards, Jim Des Lauriers

Hello, and thank you very much for the reply, James.

What I'm looking for should have the characteristics of the multi-year population cycles, including apparent population-wide changes to hormone levels that depend on the phase/year of the cycle. This is why regular annual events are not included in my search.

The premise of my hypothesis is that there is an endogenous multi-year hormonal mechanism in animal populations, and that it accelerates evolution in many ways, including speciation and gene flow. The current presumption is that if there is such a mechanism, it most likely would count years from the changes in daylight. (I guess temperature could also be a part of the mechanism, but annual changes to the length of day are much, much more regular when compared to changes in temperature.)

Best,

Janne M.

A population cycle in zoology is a phenomenon where populations rise and fall over a predictable period of time. There are some species where population numbers have reasonably predictable patterns of change although the full reasons for population cycles is one of the major unsolved ecological problems. There are a number of factors which influence population change such as availability of food, predators, diseases and climate.

Hi Ozodbek. That is exactly what my hypothesis aims to solve: it explains how it is actually an endogenous population-wide multi-year hormone cycle that causes the 'predictable' multi-year population cycles.

It is obvious that the environment affects the population size, but the proposed evolutionary mechanism is apart from those changes that are caused by the environment, because the multi-year hormonal fluctuations do manifest even without predators and if there is ample food (this has been proven by experiments by Charles Krebs and others).

The mystery of regular multi-year population cycles has been studied for over a century, but I believe I have possibly finally solved it, and what is much more interesting to me is that it looks like many human populations are undergoing this very same multi-year population-wide hormone cycle. I could be wrong, but the evidence is mounting up to support the hypothesis.

Janne; Is the hormone cycle predicted to be responsible for changing population numbers or is it the other way around? Jim Des Lauriers

James,

The hormone cycle is predicted to be responsible for both 1) increasing population numbers and 2) increasing sexual behavior and changes in physiology, like larger testicles etc. The hormone cycle is independent from the environment, since the cycles do appear even without predators or limited food supply, and pathogens alone cannot drive the cycles according to studies.

(Regarding human populations, high levels of sex hormones occurred in Western human populations during the 1960s and 70s, and now 2000s and 2010s were a time of low testosterone levels (in individuals in reproductive ages). The full length of one cycle in human populations is about 80 years, so the next decade when sex hormone levels will be high is presumably the 2040s.)

I understand that this is a hugely bold suggestion, but like I said, there is a lot of evidence to support the premise that it's an independent hormone cycle that creates the cycles, and that Western human populations are undergoing that very same cycle. But the correlations are there, and they're numerous.

Here's a direct link to the project webpage: https://jannemiettinen.fi/FourthTurning/

Janne M.

Janne; I read your abstract just now...and will work on the body of the paper. Maybe you address it later, but, since you are familiar with the lemming stuff, here's my sticking point with the idea. Whether these hormone cycles are endogenous or produced by some environmental cue needs to be unambiguously demonstrated. Your argument hinges on it.

All (all those I know anything about) the boom and bust species' numbers are modulated by the intrinsic rate of increase and food supply. The hormone cycles are simply embedded in that selective regime but doesn't drive it. Your study evidently rejects those two sentences. Can you clear that up for me?

In your abstract you suggest that the boom portion of the cycle provides new satellite populations that are the raw material for speciation. Lovely! I like that part of the hypothesis. Cheers, Jim Des Lauriers

James,

Studies have shown that you cannot stop the cycles by removing predators or adding food. And starting the cycles experimentally is impossible. So the environment is unlikely to cause the cycles or the multi-year fluctuations to hormone levels. No one has succeeded in explaining how it would work, while taking into account that the predator removal and adding food does not affect the cycles (except that it obviously does modify the curves, which is expected when you change the environment). So I believe the cause is elsewhere, and the multi-year population-wide hormone cycle explains all the aspect of the cycle, and in different species; something that no hypothesis has been able to do until now.

And if the premise of human populations having this very same hormone cycle is true, like the statistics (and proxy statistics) seem to indicate, then it is even less likely that it would be the predators, pathogens, and/or food supply issues that would drive the cycle and the fluctuating hormone cycles, since humans live in a totally different environment compared to wild animal populations.

Sure, there have been studies that what if chemicals/pollution/cellphones/soy/etc. have caused the declining testosterone levels, but the results are very limited. It's quite easy to blame the environment for changes in hormone levels, and I too used to believe the environment holds the answers to changes in human hormone levels, but without evidence those claims hold little value.

I'm thrilled to hear that you're interested in this topic, and would very much like to hear your thoughts on it. The hypothesis has a huge scale, and it adresses issues on many levels, from micro to macro, from past events to possible future events. But everything is always based on the theoretical biological framework.

Best,

Janne M.

Janne; Well, thanks. I'll read some, follow this thread and try to catch on...this is a topic far from my ant ecology. Cheers, Jim

Consideration of ecological scale is of fundamental importance in understanding animal population cycle i.e. population growth and decline. In population cycles, cyclical oscillations, are repeating rises and drops in the size of the population over time. These oscillations are produced due to density-independent and density-dependent limiting factors. Density-dependent regulation can also be due to behavioral or physiological changes in the organisms regulated by body hormones, resulting, in response to high population density, to emigrate in search of new place to live, and during the process of emigration some dies, leading to a fall in population density.

Hi Munira,

While you are correct, no study has shown that this would drive the population cycles; not solely or with other environmental factors. It is easy to say that density would cause the increases and/or declines in the multi-year population cycles (that have clear population-wide fluctuations in hormone levels), but there is no proof of that. Nor that the increasing density would cause the multi-year population-wide hormonal changes, which has also been studied.

I'm not saying that you're wrong, but I suspect it's a false belief, one that has been told so many times that people have begun to believe that it is the only answer. But there is no proof to support that your statement is correct when it comes to these regular multi-year cycles with regular predictable hormone fluctuations (across different species).

But if the cycle is an independent hormonal mechanism, it would explain basically all the different phases of the population cycles. And what more, I believe that many human populations are undergoing this very same cycle today.

Janne; Regarding your last observation... Something entrains the hormonal cycles. If that weren't so the individuals would quickly run out of phase with each other. What do you suppose entrains the cycle? Jim Des Lauriers

James,

It could be either a developmental cycle or a "traditional" hormone cycle like the menstrual cycle. Either way, the annual changes in photoperiod presumably synchronizes the multi-year cycle. So it would most likely by the SCN that keeps time, and then if there is some kind of a synchronization beyond that, it could be pheromones etc. (even though there is still a lot of debate how they work, the olfactory system even in humans does affect hormone levels).

But the mechanism is still unknown, and since chronobiology still has a long way to go until all the biological clocks are understood, it is unclear what the exact system driving a multi-year population-wide hormone cycle could be. I've written about this in the hypothesis (in chapters 2 and 5), but it's still an open question.

Добрый день, Янне и Джеймс. С интересом познакомился с вашим диалогом. Он касается предположений о механизмах многолетних циклов и далеко ушел от заданного вопроса (Существуют ли в тропиках циклические популяции животных?). К настоящему времени тема поиска механизмов многолетних популяционных циклов остается центральной и описаны сотни их возможных вариантов. Будут описано и даже доказано существование еще тысяч, я в этом не сомневаюсь. Это совсем другие вопросы. Вернемся же к нашему.

Я уверен, что в тропиках существуют циклические популяции. Цикличность внутреннее свойство любой популяции. Существование внутренних циклов необходимо для синхронизации с внешними циклическими процессами. Такие процессы характерны для любого климата (даже если имеется устойчивый тренд любого из факторов). Приспособиться к нужному циклическому фактору популяция может, только если имеет соответствующий по частоте эндогенный цикл. Может быть окажется плодотворным не только поиск механизмов, но и рассмотрение внутренних циклов популяции как диапазона ее адаптаций к среде?

Как вам изменение направления дискуссии в экологическую сторону. Какие циклы должны иметь популяции в тропиках, различаются ли они у разных популяций. В общем виде это вопрос зачем нужны циклы численности (плотности) тропическим популяциям?

Буду рад, если узнаю соображения коллег по этому поводу. С уважением Лев Ердаков.

Hi Lev and thank you for your comments.

The proposed mechanism is a multi-year hormone cycle, with a minimum length of 4 years on average (variation is 3-5 years, but average is 4 years). I have not been able to find such multi-year cycles in the tropic, which would also exhibit the obvious changes in physiology & behavior (= fluctuating hormone levels) according to the phase of the cycle.

I'm sure that the environment can cause all kinds of "natural" population cycles, that occur from time to time, but the key here is to find cycles that show clear marks of predictability in both length and synchronized physiological and behavioral effects on the individual animals.

The reason why I'm asking the original question is that I suspect that there are no such cycles in the tropic, since there is no way to accurately count years or seasons. Obviously there are dry and rainy seasons and other things, that may show annual periodicity, but I still doubt that there would be populations that show the same kind of predictable cyclicity as has been documented on the Northern latitudes 30 and higher.

And I have kept in mind that populations have annual fluctuations to their hormone levels, and the environment always plays a part, but the multi-year population-wide hormone fluctuations still occur, and in different species, which means that the environment is unlikely to drive the multi-year cycles. This is why I believe it is an endogenous hormonal mechanism that drives these predictable multi-year cycles. No other explanation/hypothesis covers all the aspects of these cycles.

Привет, Янне. Мне интересна тема, которую Вы исследуете. Я убежден, что среда, какие бы колебания она не имела, не может стать причиной внутрипопуляционного цикла. Такие колебания исключительно эндогенны. Вполне вероятно гормональное происхождение 3-5-летних циклов численности (для грызунов это эстральный цикл). По моим наблюдениям они обычны для большинства голарктических видов. Так что Ваше утверждение для меня особенно ценно. Хорошо бы иметь работы, где это описано. Если у Вас имеется временной ряд хорошей длины по динамике какой-либо тропической популяции (лет 20 и более) и я получу такую картинку, то с удовольствием посчитаю спектр ритмов такой популяции. Вполне вероятно, что ритмы диапазона 3-5-лет у нее окажутся и будут довольно мощными. Если имеются сведения о метеофоне таких популяций (динамики погодных факторов во время наблюдений), то можно будет найти, к какому из них синхронны искомые ритмы. Вообще-то они могут быть наведены и глобальными осцилляциями, которые захватывают и тропические районы. Если Вам это интересно, могу переслать тексты своих статей, где у разных видов найдены циклы такой продолжительности.

Моя почта: [email protected]

Lev,

I didn't quite understand your last message, since I had to rely on Google Translate to read it. Can you write it in English?

The project's webpage is located here: https://jannemiettinen.fi/FourthTurning/

Сожалею, но не знаю английского. Поэтому скажу короткими фразами. С ними автомат должен справиться.

Возможно гормональное происхождение 3-5-летних циклов численности. Например, эстральный цикл особей у полевок. Он проявляется как соответствующий 4-5-суточный ритм популяции. Наложение его, на фотопериод даст более длинный ритм. О наложении ритмов и появлении 3-летней популяционной периодичности есть описание (Lehmann, Hall, I987). У меня тоже есть работы на эту тему.

Если пришлете график ход численности животного из тропиков, то могу посмотреть спектр его ритмов.