Balance of nature: bird and seed distribution evolution (Introduction)

by David Turell , Friday, May 14, 2021, 17:23 (1289 days ago) @ David Turell

A careful study of seed distribution by bird species:

https://science.sciencemag.org/content/372/6543/682

"Mutually beneficial interactions between plants and frugivorous birds have evolved for at least 80 million years (1). Now, more than 70% of flowering plants rely on birds to disperse their seeds, and about 56% of bird families consume fruits as part of their diet (2, 3). Plants often have more than one seed disperser, and birds consume different types of fruits from different plant species, thus establishing a complex network of interactions. These networks can change considerably across space and time (4). Over short time spans, seed-dispersal interactions are dynamic and change in response to factors such as competition or abundance of the interacting partner (5, 6). However, the effects of evolutionary processes that take place over deep time are not clear (7). On page 733 of this issue, Burin et al. (8) suggest that evolutionary stability is associated with the specific role of the bird species in seed-dispersal networks.

"The role of each bird species depends on the number of interactions it establishes with potential partner plant species and how it links different parts of the larger bird-plant network (9). These interactions are the result of a set of evolutionary factors, such as coevolution, trait convergence, and diversification (10, 11). Now, Burin et al. add one more factor by demonstrating that birds with a central role in a network (that is, they interact with more plants) tend to have greater persistence through evolutionary time. A bird lineage persists longer through time if it has lower extinction rates and/or higher speciation rates, which the authors refer to as “macroevolutionary stability.” Having a low extinction rate implies longer longevities through evolutionary time, which in turn facilitates the establishment of more connections within the network because bird species have more time to coevolve with plants, whereas having high speciation rates suggests the accumulation of more sister species that are expected to have similar traits and play similar roles in the network and can therefore act as a replacement if a species goes extinct

***

"Most studies on the assembly of seed-dispersal networks are centered at ecological time scales—that is, the time of a change in the environment that affects the relationships of organisms with each other (tens to thousands of years). These studies have shown that the cores of seed dispersal networks are stable to annual fluctuations in fruit availability or the presence of specific bird species (12). Conversely, studies that focused on evolutionary aspects of seed-dispersal networks (time scale of thousands to millions of years) are primarily centered on reconstructing trait evolution of the interacting species as a proxy to detect coevolution (13). Accurately estimating speciation, and particularly extinction rates, from phylogenies composed solely of extant species is still a challenge (14, 15), making it hard to detect the footprint of evolutionary dynamics on species interactions. Although these methods are still controversial, Burin et al. take the leap to merge macroevolution and interaction networks and find a consistent and robust effect, even when accounting for the uncertainty of the rate estimates and the phylogenetic hypothesis.

***

"The direction and causality between macroevolutionary stability and the central role of a species in a network is still not understood. It is unclear whether bird species that persist over deep time become central in the interaction networks because they had more time to coevolve with the plants or whether bird species with a central role in interaction networks are more resilient to temporal changes in the availability of resources and therefore have greater evolutionary stability. Or is it a combination of the two? Moreover, exploring the processes underlying the relationship between macroevolution and species interactions improves understanding of current ecological processes."

Comment: Another ecosystem we have not considered before. All ecosystems play an enormous role in a stabilized ecology to support an enormous human population. 99% of all evolutionary forms are gone but required in the process of creating this giant bush of life in its interacting and interlocking forms. I view it as a magnificent plan by God to offer a stabilized system for all of current life forms to have a broad access for food.