When you think about doing something, you do so with a goal in mind. We know actions have reactions, but often we only look at action from one viewpoint – cause and desired effect. Yet, when you view action through only one lens, you miss the whole picture. There’s more to the story because, naturally, the effects of an action aren’t black and white. Things are never quite that straightforward.
I came across a recent paper discussing marine heatwaves and climate change and am reminded of the importance of seeing the whole picture. Nature is inherently holistic, and humans aren’t removed from that – regardless of the existing constructs that may have you believe otherwise. In times when things seem ambiguous and scary, trying to see the broader picture of our influence becomes even more important.
The need to understand our overarching influence is critical. That’s for many reasons, but the more dire reason is how greatly we influence the natural world. There are direct and indirect pathways that give way to broader impacts that come from action. Ultimately, we need to understand these pathways if we hope to save ourselves from the worst of climate change.
All actions have consequences.
Imagine you’re eating a protein bar while walking on the beach. Once you’ve finished said protein bar you realize you have no pockets and no trashcans are around. So, you decide to drop your wrapper. What’s the big deal? You move on with your life.
Then a seabird comes by, smells the food, and swallows the wrapper whole. Action and reaction. Your action directly led to a seabird eating a piece of plastic.
But then the seabird flies back to its nest to feed its chick what it just picked up, the plastic wrapper. This plastic then blocks the chick’s digestive tract. Therefore, your action has indirectly led to the chick’s starvation. Morbid, but you get the point.
Direct vs Indirect Effects
When talking about ecology and conservation, it’s important to understand how an ecosystem functions. One of the best ways to do so is by trying to understand the broader impacts of change. That is the direct and indirect effects of certain actions. Learning more about direct and indirect effects clues us into how greatly variables influence other things and how compounding of an effect they may have.
Direct effects
Direct effects are consequences that come from direct influence and involve two parties. On one hand, this can be in the form of two organisms interacting. But it can also be in the form of environmental change directly influencing the behavior or physiology (i.e. bodily functions, like the respiratory or digestive systems) of an organism. Both physiology and behavior play huge roles in determining an organism’s ability to live!
Physiology helps organisms detect predators and prey. Physiology also determines coordination, endurance, ability to manage stress, and phenology (which is the timing of life history events, like migrations and laying eggs). Behavior changes are also important to note and can play a part in physiological responses. Direct effects on behavior influence things like location, activity levels, and the amount of energy an organism uses.
Examples of direct effects:
Direct effects are linear actions that are more understood because the cause and effect are straightforward. A bee pollinating a flower or a frog catching and eating an insect are classic examples of a direct effect. But there are eight main types of direct effects and these are classified by whether the net effect is positive, negative, or neutral.
Herbivory
This is when an organism eats a plant. A caterpillar eating a leaf is an example of herbivory. The net effect is positive for the herbivore, but negative for the plant.
Predation
When one organism (predator) eats another organism (prey). A lion eating a zebra, for example. Similar to herbivory, the effect is positive for the predator but negative for the prey.
Competition
In the case of direct effects, competition is when two organisms compete for the same resource. This can happen to secure things like food, a mate, or space. Two trees growing taller to gain better access to sunlight is an example of direct competition. This is a net negative for both parties.
Parasitism
One organism is dependent on a host to live, at the expense of the host. Fleas and dogs are an example, where the fleas are the parasite and the dogs are the host. Parasitism is positive for the parasite, but negative for the host.
Mutualism
Two species benefit from interacting with each other. Clownfish and sea anemones are mutualists that positively affect each other. The net effect here is positive for both parties.
Commensalism
One organism is positively affected but the other party sees no change. Remora fish and sharks have such a relationship.
Amensalism
One organism is negatively affected but the other party sees no change. Black walnut trees, for example, release a toxin into soil that kills surrounding plants.
Neutralism
Coexisting organisms that have neither a positive nor a negative effect on each other. This one is hard to prove, but one example is seen through some species of Lactobacillus and Streptococcus bacteria which can coexist without positively or negatively affecting each other.
Indirect Effects
Unlike direct effects, indirect effects require a third party to facilitate the action. One organism affects another but only because of that third party. In other words, organism A affects B, which then affects C. These effects are complex and add to the intricacy of ecosystems.
Furthermore, indirect effects include a broad variety of interactions that can happen through chains of direct interactions. Although indirect effects operate in a more roundabout way, the consequences are often just as – if not more so – impactful as direct effects.
Examples of indirect effects:
There are two main ways an indirect effect can occur, the first is through changing dynamics. This is an interaction chain where organism A affects the abundance of organism B, which then affects organism C. The second, interaction modification, happens when organism A changes a characteristic of organism B, such as behavior, which then affects organism C.
Interaction chains:
Keystone predation
Here, a predator (organism A) causes a decline in the number of its prey (organism B), which allows a competitor species (organism C) to grow in numbers. An example of this is fish increasing the predation of sea stars, a keystone species, which then lets mussels, the sea stars’ competitor, have more resources leading to an increase in mussels.
Trophic cascade
A predator influences its prey’s resources by reducing the abundance of the prey. An example of this is a bird having a positive effect on a plant species by reducing the abundance of caterpillars that eat the plant species.
Apparent competition
This is when an increase of one organism leads to a decrease of a second organism due to enhanced predation by a shared predator. For example, an eagle preys on snakes (organism 1) and rabbits (organism 2). As snake numbers grow, so do the eagle numbers because the eagles now have more to eat. The rising number of eagles then leads to a decline in rabbits. So, as snake populations increase rabbit populations decrease.
Exploitative competition
When two predators eat the same prey, the decline of prey species can negatively affect the second predator. For example, fish and crabs are two predators that eat sea stars. With both predators relying on sea stars for food, sea star numbers quickly fall. Suppose fish are better at catching sea stars, that causes a decline in crabs because the scarce prey is going to the fish.
Interaction modifications:
Habitat facilitation
An organism indirectly improves the habitat of a third organism through its interaction with a second organism. For example, freshwater plants help algal filaments to grow, which then are used as habitat for snails.
Indirect mutualism
This is when two organisms positively impact each other through a third organism. For example, ants that live and rely on acacia trees for food will protect the trees from other herbivores. So, ants indirectly positively affect acacia trees by deterring those herbivores while also benefitting from using the trees’ resources.
Indirect commensalism
Here, one organism benefits another through its interactions with a shared third party. An example is beavers cutting down cottonwood trees, which makes the leaves on cottonwood trees more nutritious. This lets beetles who feed on the leaves to grow and develop faster, so they are positively affected by the interaction between the beavers and the cottonwood trees.
Nature responds to change but can be limited.
Not surprisingly, how an organism responds to a situation is determined by how it evolved. Past conditions shape what something can and cannot tolerate. So, there’s potential for a mismatch between the past and the now-changing conditions.
If there’s room for adaptive responses, survival can (in theory) prevent population declines and provide additional time for the organisms to adapt to new conditions. Maladaptive responses, on the other hand, make organisms less fit as environments change and could accelerate population declines.
The impacts of climate change are far-reaching and dynamic.
Climate change is affecting how we, and other species, interact with the environment and each other. Ecological interactions are changing! The impacts of climate change include warming temperatures, changes in the water cycle, increases in the frequency and intensity of extreme weather events, and rising sea levels. Even still, all of these things will fundamentally transform current ecosystems and food webs.
We’re already seeing the effects. Species distributions are changing, whole dynamics are changing, biodiversity it changing, and species are going extinct at alarming rates. For us, these impacts threaten our health by affecting the food we eat, the water we drink, the air we breathe, and the weather we experience.
The direct and indirect effects of anthropogenic climate change:
Environmental change puts a lot of stress on those who undergo this change. If we have any hope of mitigating the consequences of anthropogenic climate change, we need to first understand the mechanisms that underlie biological change. That is, the mechanisms that drive responses to global change: direct and indirect effects.
Species don’t live in isolation within their physical environments, and the direct effects of climate change are likely to be compounded by indirect effects that result from altered interactions with other species. Climate change effects are not observed in a bubble! The bottom line is that climate change affects both direct and indirect interactions of species by changing conditions and resources in their habitats.
Direct effects of climate change:
Direct impacts of climate change include physical and chemical changes in the environment that directly affect species.
Some examples include:
- Changing temperatures are leading to a change in species distributions and cause extinction events if species can’t cope with new temperatures.
- Pollution has overarching negative direct effects on environmental and human health.
- Sea level rise and warming temperatures directly lead to ocean acidification.
Indirect effects of climate change:
Indirect impacts of climate change are associated with changes in climate and impacts on ecosystems, which include compounding effects on species.
Some examples include:
- Changing temperatures and water availability affects soil health which then leads to a decline in plant biodiversity and decreases agricultural yields.
- Rising temperatures indirectly lead to massive die-offs due to algal blooms.
- Increased extreme weather events like flooding can lead to the increased spread of pathogens.
Responsibility is key.
We know climate change is a problem, but how much? We can try to figure this out by using models to examine indirect and direct effects. But really we just need to move forward. We can’t pretend there’s no cost, but we also can’t pretend we can continue per the status quo. The more we understand the problems, the better we can find solutions. Trying to scrutinize our actions to try and predict the direct and indirect effects is potentially too extreme, but everyone needs to understand that actions have consequences, even in our daily lives.
We need to understand that we, directly and indirectly, influence our environment, just like our environment directly and indirectly influences us. Assessing the joint impact of direct and indirect effects of global change on populations will be necessary to effectively predict and mitigate biodiversity loss. Although the complexity of ecological systems makes accurate predictions difficult to achieve, an increased understanding can hopefully improve our ability to maintain biodiversity in the face of myriad environmental challenges.
Let’s get out of our human-centered bubble and realize there are broader implications to our actions. Overconsumption, for example, has been normalized far beyond the point of sanity and is done without regard. So, let’s create a more sustainable world by being more mindful and more compassionate to others and the environment.