Balance of nature: ecosystem survival rules (Introduction)

by David Turell , Wednesday, June 28, 2023, 19:31 (513 days ago) @ David Turell

It may be do to similarities that fit:

https://www.quantamagazine.org/the-key-to-species-diversity-may-be-in-their-similaritie...

"More than four decades ago, field ecologists set out to quantify the diversity of trees on a forested plot on Barro Colorado Island in Panama, one of the most intensively studied tracts of forest on the planet. They began counting every tree with a trunk wider than a centimeter. They identified the species, measured the trunks and calculated the biomass of each individual. They put ladders up the trees, examined saplings and recorded it all in sprawling spreadsheets.

"As they looked at the data accumulating year after year, they began to notice something odd in it. With more than 300 species, the tree diversity on the tiny 15-square-kilometer island was staggering. But the distribution of trees among those species was also heavily lopsided, with most of the trees belonging to only a few species.

"Since those early studies, that overstuffed, highly uneven pattern has been seen repeatedly in ecosystems around the world, particularly in rainforests. The ecologist Stephen Hubbell of the University of California, Los Angeles, who was part of the team behind the Barro Colorado surveys, estimates that less than 2% of the tree species in the Amazon account for half of all the individual trees, meaning that 98% of the species are rare. (my bold)

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"A new ecological modeling paper in Nature by James O’Dwyer and Kenneth Jops of the University of Illinois, Urbana-Champaign explains at least part of this discrepancy. They found that species that should seemingly be head-to-head competitors can share an ecosystem if details of their life histories — such as how long they live and how many offspring they have — line up in the right way. Their work also helps to explain why one of the most successful ways to model ecologies often arrives at accurate results, even though it glosses over almost all we know about how organisms function.

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"Back in 2001, the paradoxically high biodiversity on Barro Colorado Island inspired Hubbell to propose the groundbreaking neutral theory of ecology. Traditional ecology theory stressed the competition for niches between species. But Hubbell pointed out that species might not really matter in that equation because, in effect, individuals compete for resources with members of their own species too. He suggested that patterns of diversity in ecosystems might largely be the products of random processes.

***

"When the researchers allowed their model to progress through time, putting each simulated individual through its paces, they found that certain species could persist alongside each other for long periods even though they were competing for the same resources. Looking deeper into the numbers for an explanation, Jops and O’Dwyer found that a complex term called effective population size seemed useful for describing a kind of complementarity that could exist among species. It encapsulated the fact that a species could have high mortality at one point in its life cycle, then low mortality at another, while a complementary species might have low mortality at the first point and high mortality at the second. The more similar this term was for two species, the more likely it was that a pair could live alongside each other despite competing for space and nutrition.

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"The researchers wondered if similar patterns prevailed in the real world. They drew on the COMPADRE database, which houses details about thousands of plant, fungal and bacterial species collected from a variety of studies and sources, and they zeroed in on perennial plants that all lived together in the same research plots. They discovered that, as their model had predicted, the plant species that lived together had closely matching life histories: Pairs of species living in the same ecosystem tend to be more complementary than randomly drawn pairs.

"The findings suggest ways in which species that are not necessarily in direct competition could work well alongside each other without invoking distinct niches, said Annette Ostling, a professor of biology at the University of Texas, Austin. “The coolest part is that they are highlighting that these ideas … can extend to species that are pretty different but complementary,” she said.

"To William Kunin, a professor of ecology at the University of Leeds in England, the paper suggests one reason why the natural world, for all its complexity, can resemble a neutral model: Ecological processes may have a way of canceling each other out, so that what seems like endless variety can have a simple outcome he described as “emergent neutrality.” Hubbell, for his part, appreciates the expansion of his initial work. “It offers some thoughts on how to generalize neutral models, to tweak them to put in a bit of species differences, expanding and contracting to see what happens to diversity in a local community,” he said."

Comment: please take note of my bold. If 98% are small populations, thinking of a safety-in- numbers for species survival, a large species has more genetic variety to help secure adaptability and therefore more chance for survival. Also, the 98% small population brings to mind Raup's 99.9% loss figure. They fit. There is a similarity here to animal ecosystems with top predators surviving as species for long periods.