In the course of global warming, the distribution areas of many birds are shifting. At first glance, this leads to an increase in the number of species, especially at higher altitudes and northern latitudes. But as a more detailed analysis now reveals, this belies a phylogenetic impoverishment: In many places, the number of closely related, ecologically similar bird species is increasing, while rarer birds with unique evolutionary and ecological characteristics are disappearing.
Blackbirds, great and blue tits, magpies and house sparrows – these common birds can now be seen on green spaces in many regions of Germany, but there are also rarer species such as storks, bluethroats and little owls. But what will that look like in 2080? How is climate change affecting these species communities? Which bird species will we find in Hesse and the rest of the world in the future?
It also depends on the degree of relationship
Alke Voskamp from the Senckenberg Biodiversity and Climate Research Center Frankfurt (SBiK-F) and her colleagues have found the first answers. “We studied the effects of global warming on land on the regional distribution of birds around the world,” says Voskamp. “The focus was on the effects on species richness as well as on various aspects of phylogenetic diversity, in particular how closely the species are related to each other.” To do this, the team evaluated the distribution data for 8,768 bird species worldwide and analyzed how many at a regional level Lineages in species communities are lost or added as species follow climate change, thereby shifting, expanding, or contracting their ranges.
“The study is not just about how many species there are in the end, but also how diverse the bird community is,” explains Voskamp’s colleague Susanne Fritz. “Two species of sparrows, for example, form a completely different community than a sparrow and a little owl – the second community is phylogenetically and ecologically much more diverse than the first.” Data for two climate scenarios – one with effective climate protection (RCP 2.6) and one with average emissions of greenhouse gases (RCP 6.0).
Increasing phylogenetic homogenization
The evaluations revealed that, at first glance, species diversity even seems to be increasing, especially in the northern latitudes. With climate change, more bird species are expanding their ranges to higher elevations and more poleward. As a result, the number of species tends to be lower in tropical regions and many areas in the southern hemisphere, but higher in northern latitudes such as northern North America and Eurasia. The problem, however, is that “the bird species that are being added are mostly closely related to one another and to the species that are already present in this area,” reports the team. At the same time, species that do not belong to these kin groups are disappearing from these areas.
Such community restructurings are projected to occur around the world, albeit to varying degrees. According to the researchers, large parts of Europe are also affected. Overall, she believes, this development is leading to phylogenetic homogenization in many regions – with potentially negative consequences for ecology: “The diversity of lineages, i.e. the phylogenetic structure of the species community, is very often related to the diversity of the characteristics of species and thus also to it on their roles and functions in ecosystems,” explains Voskamp. “Change thus means that the ecosystem functions that birds perform could also change in the future – with consequences for food webs as well as for seed dispersal and pollination of plants.”
Source: Senckenberg Research Institute and Natural History Museums; Article: Proceedings of the Royal Society B – Biological Sciences, doi: 10.1098/rspb.2021.2184