Bowler et al. (2020) Impacts of predator-mediated interactions along a climatic gradient on the population dynamics of an alpine bird. Proceedings of the Royal Society B, 287, https://doi.org/10.1098/rspb.2020.2653.
Whether or not a species will survive in an area can usually be broken down into two broad categories: how suitable the environmental characteristics of that area are (temperature, elevation, rainfall), and how it interacts with the other species found nearby. Early ecological theory predicted that in harsh environments, how a species interacts with other species wouldn’t matter as much, and would only come into play when the area was easier for the species to inhabit.
Yet more modern work often contradicts this theory. For instance, the Alternative Prey Hypothesis (APH) suggests that in areas where there are relatively few species as a result of harsh climates, interactions between those few species will be relatively strong. For example, if a prey species declines one year, then its usual predator must find an alternative prey species. This creates an indirect interaction between the two prey species, which is particularly strong in harsh environments where there aren’t other species around.
One of the most worrying things about the global phenomena that is climate change is that we are so uncertain of its exact effects on our planet’s biodiversity. There are the more obvious questions that need to be asked, like how will warming temperatures affect species ranges, and will cold-tolerant species face significant population losses?
Yet there are other less obvious concerns out there which need to be tested. For instance, seeing as there are far more fish-like birds in Antarctica, do colder temperatures lead to birds being more fish-like? And will a warming climate therefore lead to a world devoid of fishy birds? This week’s researchers had a different theory, and used some interesting statistical techniques to test it out. The project was inspired by a particularly memorable pizza consumed by one of the researchers, in that it looked at “fishiness, birdiness, lack of fungal toxicity, and effects of prolonged heating”*.
When we think of climate change we tend to think about extreme weather events and melting ice caps, but the way in which our environment is changing is giving the planet more than just unseasonal weather. Phenology (the timing of biological events in nature) dictates when an organism begins a given part of its life cycle, and changes in phenology are one of the most frequent responses to climate change. Take bees and flowers; bees feed on the flowers of certain plant species, and in turn spread the plants’ pollen for them. They both depend on the other being around at the same time, and if flowers bloomed too early, or if the bees came around before the flowers were “ready” for them, both parties would suffer.
Such a mismatch is known as an asynchrony, and it is hypothesized to cause population declines due to the harmful impacts on one or more of the interacting species involved (see another recent post to understand how the loss of one or more interactions can lead to cascading effects throughout a local community). While many theoretical models have investigated these processes, today’s authors wanted to combine such models with long-term data on the phenology and population size of great tits (Parus major). Great tits rely on a small period of insect abundance to feed their young, and as such the more closely they can match the needs of their young to the abundance of insect populations the more they will increase their fitness.
Image Credit: European Wilderness Society, CC BY 4.0, Image Cropped
What comes to your mind when you think of Wilderness? Maybe it is a dense rainforest filled with a cacophony of bird calls, or plain filled with lagre grazing animals and free-roaming carnivores? They certainly qualify, but by definition, Wilderness is any area that hasn’t (or has only slightly) been modified by human activity in the past. This means that Wilderness areas can be incredibly diverse, from the aforementioned tropical forest to a murky swamp. These areas represent nature in its purest form, with the absence of human interventions allowing for dynamic, open-ended natural processes. These processes not only create marvelous landscapes and offer refuge for species, but also provide many benefits for humans.
Climate change has resulted in multifarious changes in the natural world, not the least of which being where one can find a given species. Because areas are growing warmer, some species are shifting their habitats to stay within the type of environment that they like. The thing about shifting habitats though is that a species that shifts is likely to run into/need to compete with another species that is already there. Competition affects the growth and dispersal of organisms, so it follows that this should have an effect on the ability of a given species to shift or expand its range. However, most studies do not take competition into account when predicting range expansion.
A classic example in the scientific literature that did take competition into account was that of the gray squirrel invasion of Britain. Gray squirrels invaded and subsequently displaced the native red squirrels, but competition appeared to have no influence. Instead, a pathogen appeared to be the likely cause of the contraction of the red squirrel range. This example, however, comes from an observational study of a single replicate. Today’s authors instead conducted a manipulative lab experiment to test for the effects of competition on range expansion.
We here at Ecology for the Masses recognize the harm of climate change and the danger that it poses to countless species the world over. Part of climate change involves extreme climate events such as floods, droughts, unusual cold spells, or cyclones, all of which can be devastating to natural systems. By and large these events are seen as negative, and rightfully so! But today’s paper offers another perspective on extreme climate events: their potential for driving evolution towards increased resilience.
Now, I’m not saying that these extreme climate events are good. I dislike them just as much as the next person with a shred of concern about the natural world. That being said, the authors raise some interesting points about the evidence that exists for these events being a positive force for evolution and adaptation. As such, I want to touch on a few of those points, address some issues with this ‘silver lining’, and talk about what it means going forward.
What Evidence Exists
Extreme climate events result in massive losses of organic life, local extinctions, and can drive range shifts. This is quite costly from not only an ecological point of view, but also a social and and an economic one. Due to these costs, a significant amount of effort and money has been dedicated to working on issues associated with these events. Interestingly enough, despite the negative connotations and costs associated with extreme climate events, there is emerging empirical evidence for a “benefit” in that they can cause non-random mortality (see Did You Know?), driving rapid evolution and adaptation.
Scientific theory has predicted that when extreme climate events occur in such a way that they select against weak individuals, but aren’t so extreme that “tougher” individuals cannot live, then these more tolerant and stronger individuals can persist in populations/areas undergoing extreme events. If these tougher individuals can pass on their genes, then a population can rapidly adapt to these extreme conditions. For example, a study showed that a severe cold snap selected for cold tolerance in green anoles (Anolis carolinensis), and similar work has shown that heatwaves selected for thermal tolerance in kelp. While plenty of the lizards/kelp didn’t have the proper traits to survive these extreme temperatures, some of them did. And because they passed on those genes to the next generation, the population is better-suited to survive future extreme temperatures.
Did You Know: Non-Random Mortality
Evolution is a fact of life, and the driving force behind the persistence of life on our planet. However, what you may not know is how evolution actually results in changes in a population/species over time. Individual organisms don’t evolve, species do. So how does that work? Well, it all has to do with how often certain individuals pass on their genes. “Survival of the fittest” refers to the biological concept of “fitness”, which is how good a given organism is at passing on its genes. So in order to be the most fit, you have to pass on the most genetic material, relative to other members of the population. This is where non-random mortality comes into play. Non-random mortality means that there is a pattern behind the death rates. Put into other words, the individuals that survived had something that the ones that died did not. This is how evolution works slowly over time, non-random mortality means that individuals with a given trait tend to die less often than those that don’t have that trait, which means that that trait gets passed on more often than others. Eventually, that trait will become the new normal for that population/species, and evolution has occurred.
What This Means
The potential for extreme events to select for resilience and drive rapid adaptation means that groups dedicated to conservation and preservation of species and ecosystems may be able to proactively anticipate future events. The authors highlight the difficulty inherent in studying non-model organisms for traits/genes that may promote persistence to future climate events, as it involves a LOT of background research to understand the mechanisms behind such persistence. However, to use the anoles from earlier as an example, there are better ways. If one was to go to an area that recently suffered a cold snap like those anoles did and collect the survivors, chances are that most of those survivors have the cold-tolerance trait. By selectively breeding/relocating those survivors conservation workers could prevent future die-offs due to cold snaps.
Problems With These Approaches
This all sounds great, right? No issue? Well, not quite. Just because a given trait may promote persistence to one stressor (the environment) does not mean that it promotes persistence to all others (like disease). Another issue with this silver-lining of adaptation and rapid evolution is the bottleneck effect: extreme events cause mass die-offs. Though the survivors may have a trait that allows them to persist in extreme events, the reduced population size of the survivors may result in such a marked decrease in genetic diversity that the population fails eventually anyway due to the issues associated with inbreeding.
Extreme climate events are an unfortunate reality, and they are only predicted to get worse and become more frequent. Today’s paper offers a pleasant silver lining to that very grim reality, as it highlights the potential for these events to drive evolution and selection to extreme conditions. It may not be as good as not having these events in the first place, but the authors bring up an important point by drawing attention to the evidence that exists for populations adapting to these extreme conditions, many of which seem to be driven by human-induced climate change. I’ve recently re-read Michael Crichton’s Jurassic Park, and I can’t help but think of a quote from the character Dr. Ian Malcolm’s as I was reading this paper: “The planet has survived everything, in its time. It will certainly survive us”.
Adam Hasik is an evolutionary ecologist interested in the ecological and evolutionary dynamics of host-parasite interactions. You can read more about his research and his work for Ecology for the Masses here, see his personal website here, or follow him on Twitter here.
Language is important. It’s a lesson many biological scientists would have learned a long time ago if we hadn’t kept social sciences at such a wary arm’s length. Ecologists have a tendency to label and relabel ecological concepts (anyone up for a debate about the word ‘niche’?), species and even global phenomena (think global warming vs. climate change) based on anything from shifts in public perception to new findings that challenge our earlier labels.
One of the few positives to come out of a recent spate of catastrophic weather events has been the fact that climate change is now nigh on undeniable, and more people than ever are working to prevent its future effects. Yet there are parts of the world in which climate change is more than the progenitor of random disasters, where it has become an everyday reality.
One such area is sub-Saharan Africa. Despite being one of the poorest regions of the world, it’s also a region that has enormous potential for agricultural transformation, helping to solve not only local food crises, but global ones as well. A prominent example is Kenya, where the agricultural sector contributes to over half of the Gross Domestic Product, and provides food and employment for more than 80% of the population. Working for Kenya and other countries in the region is the chance to avoid mistakes made by other regions in the past, as they benefit both from hindsight and improved technology. Yet working against them is that encroaching threat of climate change.
It’s a topic that Assistant Professor Esther Ngumbi, of the University of Illinois has been vocal about. Esther grew up on a farm in rural Kenya, and has witnessed the effects of increased drought and weather variability over the last decade. Esther’s work on food security in Africa has seen her work published in everything from the Journal of Chemical Ecology to Times Magazine.
At 2019’s BES Annual meeting, I got the chance to speak to Esther about everything from African governments to the shifting of climate baselines.
Recent responses to climate change reveal the drivers of species extinction and survival(2020) Román-Palacios & Wiens, PNAS, https:/doi/10.1073/pnas.1913007117
We tend to think of climate change as bad, and despite the fact that some organisms will benefit from it, many others won’t. A big part of why we consider it bad is that species are predicted to be lost at an alarming rate, with some estimates as high as 54% of all organisms going extinct. An issue with these predictions is that they tend to assume that species will track their preferred temperature and precipitation conditions, but this eliminates any ability of organisms to adapt to their new normal over time.
Today’s authors wanted to use data from previous studies to estimate how species adapt (or don’t) to climate change. Although previous work has shown that climate change is detrimental for many species, this study aimed to learn if it was due to changes in the overall temperature, changes in the extremes (i.e. how hot the hottest day is), or was it the sheer speed of change that did organisms in. Read more
Increased reproductive success through parasitoid release at a range margin: Implications for range shifts induced by climate change(2020) MacKay, Gross, & Ryder, Journal of Biogeography,https://doi.org/10.1111/jbi.13795
Predicting the response of organisms to climate change is a challenge for ecologists and wildlife managers alike. Fortunately, some responses are common enough that it is still possible to make fairly accurate predictions about them without too much information. One common response is that of the range shift, whereby a population of organisms facing some alteration (eg. climate change) in their current habitat, making it unfavorable, begin to move to another location. This allows them to track favorable environmental conditions and possibly mitigate any negative effects of climate change.
Sounds easy, right? Just pack it all up and move when things get hard? Well, for some organisms it may be that simple (looking at you, birds), but for others (like trees) it is significantly harder to do so. Trees (and other plants) are limited in that they depend on other organisms or things like wind to help disperse their seeds. Making things even more difficult are plant species that depend on specific pollinators, and in order for a successful range shift to happen trees AND their pollinators have to make the move. Today’s authors wanted to study how relationships between trees and their pollinators changed at the leading edge of a range shift, allowing them to understand how and why trees succeed during a range shift.