you're reading...


Comparing all the ecosystems ever reveals cool patterns about their structure

[Original paper: “Ian A. Hatton et al. (2015) “The predator-prey power law: Biomass scaling across terrestrial and aquatic biomes” Science vol. 349 iss. 6252 p. 1070”]

Sometimes finding patterns in data helps answer questions; sometimes it asks questions. The study we’ll discuss today does the latter, and the question it asks is a big one: what is the relationship between an ecological community and the individuals that make up that community?

One of the most beloved and hotly debated theories in biology is Kleiber’s law, which poses a relationship between an individual’s mass (m) and its metabolism (b), i.e. how much energy it uses up. The mathematical formula is b = a*m^k, where a is a constant corresponding to the metabolism of an organism that weighs one gram (this in general varies from species to species), and k is an exponent that’s 3/4 if you ask a biologist, 2/3 if you ask a physicist, but definitely less than one. An animal’s mass, then, (e.g. how much biologically active tissue they have) has a huge influence on its overall metabolism.

Screen Shot 2015-11-14 at 3.34.09 PM



Fig. 1: A gorilla and a mouse, animals with two very different metabolic rates.

The important thing about k < 1 is that per unit mass, metabolism decreases as organism size increases. A gorilla typically weighs about 8000 times more than a mouse; we can probably guess that a single gorilla uses up more total energy and eats more than a single mouse (Fig. 1). However, with Kleiber’s law we can predict that if we had 8000 mice instead of the one gorilla, they’d collectively have a metabolism about 10 times that of the gorilla, and eat about 10 times more. Now imagine replacing the gorilla with the equivalent amount of bacteria – that’s a hungry bacterio-ape!

Screen Shot 2015-11-14 at 3.11.48 PM


Fig. 2: Data for Kleiber’s law. Despite a huge range of individual sizes [.00000000001 to 100000000 grams], over 1500 organisms fall very closely along the same relationship of how fast they can grow (“Maximum production”) and how big they are. Theory geeks like myself go crazy for straight lines on logarithmic plots [by ‘logarithmic’ I mean how things change along the axes], especially with so many points!

Kleiber’s law, however, is a theory about individuals, and the relationship between body mass and metabolism has been known and tested experimentally for decades. What the authors of this study uncovered was a really interesting link between this individual-level phenomenon and similar relationships at the ecosystem level. By compiling data from 2260 ecosystem studies across the globe (Fig. 3), they uncover similar k-exponent relationships for ecosystem ‘production’ (one can most simply think of this as growth) and predator-to-prey ratios.


Screen Shot 2015-11-15 at 9.31.25 PMScreen Shot 2015-11-15 at 9.31.10 PM


Fig. 3: Each point corresponds to a place data was taken from for this study, all over the world; each color represents lakes/coasts/rivers (blue), open ocean (yellow), land plants (green), and land animals (red). It’s… a lot of data.




Whether it’s a lake, a river, an ocean, a forest, a savannah – same stuff. As we look at communities with more mass in them, i.e. more or bigger organisms, we see the same sort of decline in growth as with Kleiber’s law, and the same decline in how many predators a community of prey can support. Because the pattern is repeated across all kinds of ecosystems and scales, it suggests that the phenomenon is very general and doesn’t depend on the details of any particular ecosystem, but is somehow universal to the way ecosystems are structured. As you throw more algae into a pond, more gazelles into a savannah, or more fish into a bay, fewer predators per capita of prey can survive there according to the same k-formula, and each individual grows more slowly in the same way.


Screen Shot 2015-11-15 at 9.30.07 PM

Screen Shot 2015-11-15 at 9.30.16 PM

Fig. 4: All of the data from Fig. 3 are plotted here and show the key findings of the study. The slope k varies somewhat, but the relationship stays the same. With more prey/plants/algae comes slower individual growth and fewer predators per prey that can be sustained.

The exact value for k varies slightly, but this sort of data is hard to get good measurements for, and extracting a k-value from data is not as simple a mathematical process as it’s generally thought to be (a rant for another day). The general pattern is a lot more important than the specific number. Why this metabolism-mass relationship for individuals should translate to a growth-mass relationship or a predator-prey relationship for communities is not obvious!


We can bicker about what the particular slope k should be and other details, but this impressive data set convincingly shows that a general pattern emerges for (almost, if not) all of life, at both individual and community levels. Just as metabolism decreases (per unit mass) with size in a consistent way for individual organisms, growth decreases with size in a similar manner across a range of ecosystems, as does the ratio between predators and prey.

Such robust laws are rare in ecology. The ones that emerge from this data set are quite compelling, and beg for a convincing theory as to why they happen. Such a theory would elucidate fundamental links between physiology and ecology, and would be of immense applicability to a vast range of ecosystems.

Oceanic Significance

At the same time, this study points out something really fascinating about the oceans. Ocean ecology lies at the small end of all of these mass scales, being filled mostly with microorganisms – after all, last I checked a tree is generally a bit bigger than a plankton cell. Based on this study, this means that ocean life generally supports one of the highest predator-to-prey ratios around, and that per unit mass, ocean life is hundreds if not thousands of times more productive than terrestrial life.

More than that, it suggests these differences are the result of something fundamental about how ecosystems structure themselves. Besides making ocean ecosystems markedly different than terrestrial ones, if we also consider that the ocean takes up a lot more of the earth’s surface than the continents, this also points to how ocean life has so much greater an impact on the earth system and climate than terrestrial life does.



Screen Shot 2015-11-14 at 3.16.47 PM

Fig. 5: What’s so special about ocean life? Well for one, because ocean life is in general composed of very small life forms, the predator-prey ratio is very high, and the amount of mass actually increases up the food chain, unlike how we think of most ecosystems. However, that little bit sitting at the bottom of the food chain is growing like wild compared to its terrestrial counterparts!



3 Responses to “Comparing all the ecosystems ever reveals cool patterns about their structure”

  1. Amazing to see that such varied, complex systems end up exhibiting some very predictable characteristics across many scales. Cool!

    Posted by harold | November 28, 2015, 2:29 pm


  1. […] animals tend to have higher metabolic rates than explained by their body size alone, indicating greater routine oxygen needs. Though the exact causal relationship between temperament […]

Post a Comment


  • by oceanbites 2 months ago
    Happy Earth Day! Take some time today to do something for the planet and appreciate the ocean, which covers 71% of the Earth’s surface.  #EarthDay   #OceanAppreciation   #Oceanbites   #CoastalVibes   #CoastalRI 
  • by oceanbites 3 months ago
    Not all outdoor science is fieldwork. Some of the best days in the lab can be setting up experiments, especially when you get to do it outdoors. It’s an exciting mix of problem solving, precision, preparation, and teamwork. Here is
  • by oceanbites 4 months ago
    Being on a research cruise is a unique experience with the open water, 12-hour working shifts, and close quarters, but there are some familiar practices too. Here Diana is filtering seawater to gather chlorophyll for analysis, the same process on
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #oceanbites  we are featuring Hannah Collins  @hannahh_irene  Hannah works with marine suspension feeding bivalves and microplastics, investigating whether ingesting microplastics causes changes to the gut microbial community or gut tissues. She hopes to keep working
  • by oceanbites 5 months ago
    Leveling up - did you know that crabs have a larval phase? These are both porcelain crabs, but the one on the right is the earlier stage. It’s massive spine makes it both difficult to eat and quite conspicuous in
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring Cierra Braga. Cierra works ultraviolet c (UVC) to discover how this light can be used to combat biofouling, or the growth of living things, on the hulls of ships. Here, you
  • by oceanbites 5 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Elena Gadoutsis  @haysailor  These photos feature her “favorite marine research so far: From surveying tropical coral reefs, photographing dolphins and whales, and growing my own algae to expose it to different
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  on Oceanbites we are featuring Eliza Oldach. According to Ellie, “I study coastal communities, and try to understand the policies and decisions and interactions and adaptations that communities use to navigate an ever-changing world. Most of
  • by oceanbites 6 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Jiwoon Park with a little photographic help from Ryan Tabata at the University of Hawaii. When asked about her research, Jiwoon wrote “Just like we need vitamins and minerals to stay
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  on  #Oceanbites  we are featuring  @riley_henning  According to Riley, ”I am interested in studying small things that make a big impact in the ocean. Right now for my master's research at the University of San Diego,
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Gabby Stedman. Gabby is interested in interested in understanding how many species of small-bodied animals there are in the deep-sea and where they live so we can better protect them from
  • by oceanbites 7 months ago
    This week for  #WriterWednesday  at  #Oceanbites  we are featuring Shawn Wang! Shawn is “an oceanographer that studies ocean conditions of the past. I use everything from microfossils to complex computer models to understand how climate has changed in the past
  • by oceanbites 7 months ago
    Today we are highlighting some of our awesome new authors for  #WriterWednesday  Today we have Daniel Speer! He says, “I am driven to investigate the interface of biology, chemistry, and physics, asking questions about how organisms or biological systems respond
  • by oceanbites 8 months ago
    Here at Oceanbites we love long-term datasets. So much happens in the ocean that sometimes it can be hard to tell if a trend is a part of a natural cycle or actually an anomaly, but as we gather more
  • by oceanbites 8 months ago
    Have you ever seen a lobster molt? Because lobsters have exoskeletons, every time they grow they have to climb out of their old shell, leaving them soft and vulnerable for a few days until their new shell hardens. Young, small
  • by oceanbites 9 months ago
    A lot of zooplankton are translucent, making it much easier to hide from predators. This juvenile mantis shrimp was almost impossible to spot floating in the water, but under a dissecting scope it’s features really come into view. See the
  • by oceanbites 9 months ago
    This is a clump of Dead Man’s Fingers, scientific name Codium fragile. It’s native to the Pacific Ocean and is invasive where I found it on the east coast of the US. It’s a bit velvety, and the coolest thing
  • by oceanbites 10 months ago
    You’ve probably heard of jellyfish, but have you heard of salps? These gelatinous sea creatures band together to form long chains, but they can also fall apart and will wash up onshore like tiny gemstones that squish. Have you seen
  • by oceanbites 11 months ago
    Check out what’s happening on a cool summer research cruise! On the  #neslter  summer transect cruise, we deployed a tow sled called the In Situ Icthyoplankton Imaging System. This can take pictures of gelatinous zooplankton (like jellyfish) that would be
  • by oceanbites 11 months ago
    Did you know horseshoe crabs have more than just two eyes? In these juveniles you can see another set in the middle of the shell. Check out our website to learn about some awesome horseshoe crab research.  #oceanbites   #plankton   #horseshoecrabs 
WP2Social Auto Publish Powered By : XYZScripts.com