A casual look at the world of plants and insects may suggest that nothing much is going on, but the constant struggle is anything but quiet. In this “eat, fight, or be eaten” world, scientists continue to learn how species’ various defense mechanisms, both direct and indirect, have emerged concurrently in life’s history to yield balanced, healthy ecosystems. These symbiotic relationships—sometimes involving multiple species—provide evidence for a Creator’s intelligent agency.

Symbiosis refers to a close association of two or more distinct species of life that mutually benefit one another at a cost to each of them that is less than the benefits. We’ve all seen the common example of bees and fruit trees. Bees grow a lot of long hairs that they do not directly need. These hairs are designed so that the pollen of fruit tree flowers sticks to them and rubs off when the bees encounter the tissues of flower pistils. Fruit tree flowers are designed with pistils that provide a nectar reward to visiting bees and an aroma that attracts them. The bees benefit from these nectar rewards and the fruit trees benefit from the bees pollinating their flowers. Each species pays a price for their mutualistic relationship but receives much more than what they pay for. In the case of the bees and fruit trees the symbiosis is obligate: neither species would survive without the other. Both must be created at the same time and place.

Symbiosis Studies Reveal Optimization
In a recent issue of Ecology Letters a team of ten ecologists reviewed years of scientific literature on plant-predator symbiosis.1 They pointed out that the complex and indirect nature of plant-predator symbiosis led their peers to conclude that it must be rarely manifested. However, their survey of the scientific literature led them to conclude that this indirect symbiosis was not rare but in fact, appears to be ubiquitous or nearly ubiquitous.

Plant species are constantly at risk of being wiped out by herbivores. This risk is not only a problem for plants but also for herbivores. If herbivores wipe out plant species by overconsumption, they lose their food sources and join the plant species in extinction.

Scientists have learned that ecological optimization pervades life history. The relationships among microbes, vegetation, herbivores, carnivores, parasites, and detritivores (animals that feed on decaying plant and animal tissues) appear to be consistently optimized for the benefit of all life. It takes a Mind to know what specific designs in one species would benefit that species and simultaneously maximally benefit all other species in the diverse categories of Earth’s life.

Defenses against Being Eaten
Ecologists have observed how plant species around the world possess direct defenses against herbivoresThese defenses are optimally designed so that plants can survive herbivory while preventing the herbivores from overgrazing and suffering population collapses. Examples include the thorns and spikes on cacti, hair on thistles, bad-tasting chemicals in conifer needles, waxy coatings on the leaves of ice plants, and toxins in tobacco and tea leaves. Plant species that are the slowest growing and most exposed to environmental stresses and, hence, least tolerant to aggressive herbivory, possess these direct defenses to the greatest degree.

In a few plant species, ecologists observe far more complex indirect defenses. Here, a certain plant species will reward specific predators that feed on the herbivores that feed on the plants. These reward features are designed to ensure that enough predators remain in the vicinity of the plants to prevent herbivores from overgrazing.

A well-known example of a sophisticated indirect plant defense can be seen in flowering plants that grow extrafloral nectaries—sugar-producing glands outside of the flowers. These extrafloral nectaries serve no purpose in the plant reproduction. Rather, they are designed to attract and feed certain species of insects. These insects on the plants act as bodyguards, preventing other herbivores from feeding on other parts of the plants that would threaten the plants’ survival.2

Another well-known example involves plant species that provide homes for spiders that, in turn, feed on the insects that threaten to overgraze the plants. In a review written twenty-two years ago, a team of four ecologists wrote that such indirect plant defenses, rather than being a secondary line of defense against herbivores, rank as the most potent defense line.3

The team of ten ecologists discovered that examples of indirect plant defenses are far more varied and complex than previously thought. In their scientific literature review, they found diverse plant species that emit aromas to attract predator species that prey on the herbivores that feed on the plants. They also found equally diverse plant species that grow hair tufts that house predatory mites or insects. For some plants, the hairs are sticky and trap insects, which attracts predators that then also feed on other herbivores attempting to graze on the plants. They also noted that many tree and bush species are architecturally designed to make it easier for birds to attack the herbivores feeding on the trees and bushes.

Complex Indirect Symbiosis Appears to Be Designed
As a result of their study, the ten ecologists concluded that complex designs were far more numerous than anyone realized. Complex indirect plant defenses, rather than being rare and manifesting only one or two defense designs, were likely ubiquitous and manifesting multiple independent indirect defense designs. They noted that research on indirect plant defenses was nowhere near exhaustive. Thus, they anticipated that many more indirect plant defense designs remain to be discovered and that if ecologists are diligent they will find that indirect plant defenses are indeed ubiquitous.

Such continued research will yield practical results and food for thought. A greater understanding and application of indirect plant defenses could provide farmers with the means to protect their crops from herbivore pests without the use of pesticides. This new understanding of the diversity, complexity, and pervasiveness of indirect plant defenses provides yet more evidence that a Mind lies behind the ecological optimization observed throughout life’s history.

Featured image: Extrafloral Nectaries Attracting Predator Ants
Image credit: Schwitzke et al., Anthropod-Plant Interactions 9 (2015): 497–505

Check out more from Reasons to Believe @Reasons.org

  1. Ian S. Pearse et al., “Generalising Indirect Defence and Resistance of Plants,” Ecology Letters 23, no. 7 (July 2020): 1137–52, doi:10.1111/ele.13512.
  2. Barbara L. Bentley, “Extrafloral Nectaries and Protection by Pugnacious Bodyguards,” Annual Review of Ecology and Systematics 8 (November 1977): 407–27, doi:10.1146/annurev.es.08.110177.002203.
  3. Arne Janssen et al., “Review Behaviour and Indirect Interactions in Food Webs of Plant-Inhabiting Arthropods,” Experimental & Applied Acarology 22 (September 1998): 497–521, doi:10.1023/A:1006089924336.


About The Author

Dr. Hugh Ross

Reasons to Believe emerged from my passion to research, develop, and proclaim the most powerful new reasons to believe in Christ as Creator, Lord, and Savior and to use those new reasons to reach people for Christ. I also am eager to equip Christians to engage, rather than withdraw from or attack, educated non-Christians. One of the approaches I’ve developed, with the help of my RTB colleagues, is a biblical creation model that is testable, falsifiable, and predictive. I enjoy constructively integrating all 66 books of the Bible with all the science disciplines as a way to discover and apply deeper truths. 1 Peter 3:15–16 sets my ministry goal, "Always be prepared to give an answer to everyone who asks you to give the reason for the hope that you have. But do this with gentleness and respect, keeping a clear conscience." Hugh Ross launched his career at age seven when he went to the library to find out why stars are hot. Physics and astronomy captured his curiosity and never let go. At age seventeen he became the youngest person ever to serve as director of observations for Vancouver's Royal Astronomical Society. With the help of a provincial scholarship and a National Research Council (NRC) of Canada fellowship, he completed his undergraduate degree in physics (University of British Columbia) and graduate degrees in astronomy (University of Toronto). The NRC also sent him to the United States for postdoctoral studies. At Caltech he researched quasi-stellar objects, or "quasars," some of the most distant and ancient objects in the universe. Not all of Hugh's discoveries involved astrophysics. Prompted by curiosity, he studied the world’s religions and "holy books" and found only one book that proved scientifically and historically accurate: the Bible. Hugh started at religious "ground zero" and through scientific and historical reality-testing became convinced that the Bible is truly the Word of God! When he went on to describe for others his journey to faith in Jesus Christ, he was surprised to discover how many people believed or disbelieved without checking the evidence. Hugh's unshakable confidence that God's revelations in Scripture and nature do not, will not, and cannot contradict became his unique message. Wholeheartedly encouraged by family and friends, communicating that message as broadly and clearly as possible became his mission. Thus, in 1986, he founded science-faith think tank Reasons to Believe (RTB). He and his colleagues at RTB keep tabs on the frontiers of research to share with scientists and nonscientists alike the thrilling news of what's being discovered and how it connects with biblical theology. In this realm, he has written many books, including: The Fingerprint of God, The Creator and the Cosmos, Beyond the Cosmos, A Matter of Days, Creation as Science, Why the Universe Is the Way It Is, and More Than a Theory. Between writing books and articles, recording podcasts, and taking interviews, Hugh travels the world challenging students and faculty, churches and professional groups, to consider what they believe and why. He presents a persuasive case for Christianity without applying pressure. Because he treats people's questions and comments with respect, he is in great demand as a speaker and as a talk-radio and television guest. Having grown up amid the splendor of Canada's mountains, wildlife, and waterways, Hugh loves the outdoors. Hiking, trail running, and photography are among his favorite recreational pursuits - in addition to stargazing. Hugh lives in Southern California with his wife, Kathy, and two sons.

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