Essential predators

21 11 2012

© C. Hilton

Here at ConservationBytes.com, My contributors and I have highlighted the important regulating role of predators in myriad systems. We have written extensively on the mesopredator release concept applied to dingos, sharks and coyotes, but we haven’t really expanded on the broader role of predators in more complex systems.

This week comes an elegant experimental study (and how I love good experimental evidence of complex ecological processes and how they affect population persistence and ecosystem stability, resilience and productivity) demonstrating, once again, just how important predators are for healthy ecosystems. Long story short – if your predators are not doing well, chances are the rest of the ecosystem is performing poorly.

Today’s latest evidence comes from on an inshore marine system in Ireland involving crabs (Carcinus maenas), whelks (Nucella lapillus), gastropd grazers (Patella vulgata, Littorina littorea and Gibbula umbilicalis), mussels (Mytilus edulis) and macroalgae. Published in Journal of Animal Ecology, O’Connor and colleagues’ paper (Distinguishing between direct and indirect effects of predators in complex ecosystems) explains how their controlled experimental removals of different combinations of predators (crabs & whelks) and their herbivore prey (mussels & gastropods) affected primary producer (macroalgae) diversity and cover (see Figure below and caption from O’Connor et al.).

(a) Simplified trophic interaction network of a moderately exposed rocky shore, with the components whose presence was manipulated and highlighted in red. While mussels might not interact trophically with benthic macroalgae consistently, they can comprise important consumers of algal propagules and also have strong non-trophic interactions with macroalgae arising primarily from competition for space on the shore, which might also interact with the presence of grazers. Such strong non-trophic interactions are largely absent from food web-based theoretical frameworks yet play a key role in determining the structure of algal assemblages. While crabs can feed on whelks, no predation by crabs on whelks was observed. (b) Experimental design comprising nine treatments, involving the removal of 2 species of predator and 2 groups of their prey, to measure the independent and interactive effects of predators on primary producers and test for direct and indirect effects across trophic levels.

While there were many complex interactions and outcomes of the removals, the gist of the experiment was that the loss of either predator ended up reducing the diversity and total cover of the macroalgae, mainly via the indirect effects of altered grazing abundance. They also found that shifting the dominance of one prey species to another completely changed the dominance of different macroalgae species. Thus, the top-down effects of predators on primary producers are utterly mediated by the relative changes in prey distribution and abundance. Great stuff.

The paper is worth a read, but has a lot of provisos, methods caveats and the (typical) pleas for more experimental work over longer periods. I’m just sticking with the main message here, but it’s another case of the complexity of ecology and the necessity of trying to examine simple effects from several different angles and under several different circumstances. Yes – we do need a lot more of such studies.

Chalk this paper up as another great example of good empirical evidence for the essential role of predators. Without predators, our feeble attempts to conserve ecosystems are doomed to fail.

CJA Bradshaw.


Actions

Information

7 responses

5 03 2014
Essential role of carnivores on the wane | Gaia Gazette

[…] or so revealed the essential ecosystem functions of these species (see former posts on CB.com here, here and here). The review focuses on the largest and most well-studied species, but the trends […]

20 01 2014
Černá cesta technologií | GreenAction

[…] to znamená, že pokud jeden druh, který zajišťuje základní funkce ekosystému (např. jako predaci) zanikne, je zde další, podobný druh, který je připraven převzít tohle […]

20 01 2014
Černá cesta technologií | Puntíčkovaní chrobáci

[…] to znamená, že pokud jeden druh, který zajišťuje základní funkce ekosystému (např. jako predaci) zanikne, je zde další, podobný druh, který je připraven převzít tohle […]

10 01 2014
Essential role of carnivores on the wane | ConservationBytes.com

[…] or so revealed the essential ecosystem functions of these species (see former posts on CB.com here, here and here). The review focuses on the largest and most well-studied species, but the trends […]

8 01 2014
More species = more resilience | ConservationBytes.com

[…] meaning that if one species providing an essential ecosystem function (e.g., like predation) goes extinct, there’s another, similar species ready to take its […]

21 08 2013
Don’t blame it on the dingo | ConservationBytes.com

[…] Both thylacines and devils lasted on mainland Australia for over 40 thousand years following the arrival of humans. However, a second regime shift resulted in the extinction of both these predators by about 3 thousand years ago, which was coincidentally just after dingoes were introduced to Australia. Dingoes are descended from early domestic dogs and were introduced to northern Australia from Asia by ancient traders approximately 4 thousand years ago. Today, they are Australia’s only top predator remaining, other than invasive European foxes and feral cats. Since the earliest days of European settlement, dingoes have been persecuted because they prey on livestock. During the 1880s, 5614 km of ‘dingo fence’ was constructed to protect south-east Australia’s grazing rangelands from dingo incursions. The fence is maintained to this day, and dingoes are poisoned and shot both inside and outside this barrier, despite mounting evidence that these predators play a key role in maintaining native ecosystems, largely by suppressing invasive predators. […]

11 12 2012
The biggest go first « ConservationBytes.com

[...] here on ConservationBytes.com, such as the effect of habitat patch size on species diversity, the importance of predators for maintaining ecosystem stability, and that low genetic diversity doesn’t exactly help your chances of persisting. Another big [...]

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s




Follow

Get every new post delivered to your Inbox.

Join 6,313 other followers

%d bloggers like this: