No big animals, no fertile Earth

A study recently published in the magazine Proceedings of the National Academy of Science (PNAS) reveals that animals play a key role in the transport of nutrients, but their contribution has been reduced due to the extinction or decline of many of the largest populations. In this post, we will review this study in order to understand the consequences of this fact.

INTRODUCTION

The ancient Earth was plenty of giant animals, with abundant whales in the oceans and large animals in the land. Nevertheless, their populations have been reduced for several reasons:

• The massive extinction during the late-Quaternary: about 150 large mammal (more than 44 kg) species went extinct.
• Recent and present extinctions.
• Widespread population reductions in great whales due to hunting: some whale densities might have been reduced between 66% and 99%, like blue whale (Balaenoptera musculus).
• Present environmental pressures: 27% of seabird species are threatened and anadromous fish’s populations have been reduced to less than 10% of their historical values (Pacific Northwest).

All this things are probable to have caused a shift in the global nutrient cycling. In concrete, Doughty et al. estimate a reduction to about 8% of the animals’ capability to spread nutrients in the land and about 5% in the oceans, compared with past values. Several animal groups have been identified to play a key role in this system.

1. Terrestrial animals: accelerates cycling of nutrients from more resistant  forms to decomposing matter. Some animals transfer terrestrial nutrients to aquatic environments, while others do the contrary. Even some animals, like bears and eagles, transfer oceanic nutrients to land environments by feeding on anadromous fishes.

   

   Moose (Alces americanus) transfer aquatic-derived N to terrestrial systems (Picture: BioLib).

2. Anadromous fish, fish that travel from sea to rivers to spawn their eggs (such as salmon or striped bass) and seabirds transport nutrients from sea to land.

   

   Striped bass (Morone saxatilis) is an anadromous fish (Picture: Ethan Dropkin).

3. Marine mammals, that include cetaceans, sirenians (with dugongs and manatees) and seals; have two functions in the cycling nutrient process: they transport nutrients vertically (from deep to surface waters via excrements and urine) and laterally due to migrations. [Read more about cetacean migration]

IS EARTH AS FERTILE AS IT WAS?

The answer to this question is “no”.

New findings reveal that the global nutrient distribution capacity on land has been reduced to 8% of its former value. Nevertheless, there is regional variation: most of the current capacity is on Africa because it is full of megafauna species, while in South America the capacity is at 1% of the past value. In the past, South America had the largest number of big herbivorous (more than 1,000 kg) but all of them went extinct. Nowadays, the largest animals in the continent weights about 300 kg. This difference explains the large reduction.

Arctotherium bonariense was a bear that live in South America during the late Pliocene (Picture: W.B. Scott, Creative Commons).

The current capacity of oceans is more than three times higher than for land. However, the reduction of its capacity is also important: 2% of its former value in the Southern Ocean and 14% in the Atlantic Ocean. Concerning the vertical transport of nutrients, the amount of phosphorus transported from deep to surface waters is nowadays a 23% of the original transport, with differences among oceans. Behind these reductions, hunting pressure to marine mammals is present. Nutrients that fall below the well-illuminated zone are considered to be lost. Marine mammals would have been responsible of returning nutrients to surface by feeding on the deep ocean and defecating and urinating on the sea surface.

Finally, seabirds transports 6.3 million Kg for square kilometre of phosphorous from sea to coastal environments each year (former values are not available) and anadromous fish capacity is 4% of the past value, possibly due to overfishing and habitat modification (such as damming of rivers).

Potential interlinked system of recycling nutrients. Grey animals represent extinctions.  (Picture: Doughty et al. 2015).

HOW CAN WE RESTORE THIS?

Doughty and his colleagues give some solutions to restore this situation:

• Future pastures may have less fences and more species to simulate natural pastures.
• Restoration of free-ranging wild herbivores.
• Restoration of whale populations.
• Restoration of seabird colonies and anadromous fish populations.

REFERENCES

• Doughty, CE; Roman, J; Faurby, S; Wolf, A; Haque, A; Bakker, ES; Malhi, Y; Dunning, JB & Svenning, JC (2015). Global nutrient transport in a world of giants. PNAS, doi: 10.1073/pnas.1502549112

How do whales communicate with each other?

The post of this week talks about baleen whale communication, it is, cetaceans that feed thanks to the presence of baleen plates in the mouth. In concrete, we will focus on the acoustic communication in baleen whales and, in specific, in the humpback whale case.

INTRODUCTION

Bradbury and Vehrencamp defined the term communication like the process in which an information is given through a signal from a speaker to a receiver and this receiver uses this information to decide how to respond or if the receiver responds to the signal.

There are several types of communication among marine mammals, either chemical, visual, tactile or acoustic. Due to solar light has a delimited capability to penetrate into the water, whales and other marine mammals have difficulties on visual communication with each other from a certain distance, so they use sound. In addition, chemical communication is not efficient in the aquatic environment.

COMMUNICATION PROCES IN BALEEN WHALES

Production and reception of sound

While anatomical structures related with the production and transmission of sound have been found in odotocetes (cetaceans with teeth), they have not been found in the case of baleen whales (mysticetes). Baleen whales, despite they present larynx, don’t have vocal chords. However, it is accepted that cranial sinuses, empty spaces in the skull, are involved in phonation, but its role is unclear.

The big whales are by far the most resounding marine mammals. Humpback whales (Megaptera novaeangliae) produce songs that last some hours and can be heard long distances (some kilometres). Blue whales (Balaenoptera musculus) and fin whales (Balaenoptera physalis) don’t fall behind: they produce low frequency sounds that travel more than 3,200 km of distance. In fact, blue whales produce sounds around 190 decibels, the loudest sound produced for an animal.

Blue whales (Balaenoptera musculus) can produce sounds of 190 decibels  (Picture: iTravel Cabo).

Some behavioural studies have demonstrated that all cetaceans, but specially odontocetes, have a good hearing.

Function

While some experts defend the idea that this sounds are used to communicate each other at long distances, other suggest that are used to detect the underwater relief to orientate (echolocation). Anyway, it is more accepted that they have a communicative function, including behaviours like exhibition and the establishment of the territory, among others.

THE CASE OF HUMPBACK WHALES

Humpback whales (Megaptera novaeangliae) produce complex sounds that can be heard to long distances. They are one of the most resounding baleen whales. During winter, in the breeding grounds, these whales produce long and complex songs at the same zone. These songs are different in the different zones. These songs (you can hear one of them here) lasts 10-15 minutes, but they can sing them for hours, and are composed by themes, phrases and subphrases. Each subphrase lasts some seconds and are composed by low frequency sounds (normally under 1,500 Hz).

Structure of a humpback whale song (Megaptera novaeangliae) (Picture: Hawai’s Marine Mammal Consortium).

But the complexity doesn’t end here. The structure of this musical pieces changes along winter. Not only they change the frequency and duration of the phrases and themes, but also some of them are changed by new compositions. Moreover, they also modified the composition and sequence of these themes.

Anyway, all the whales at the same area sing the same song and all of them modify it at the same rate to other mates. So, they learn from other mates.

Some studies highlighted that adult males are the only that produce this songs. So, it indicates that this songs play a role in reproduction, similar to bird songs. Therefore, these songs indicate to females the sex, the species, the position and that he is ready to compete with other males and he is ready for mating.

In addition, according to Mobley y Herman (1985) the fact that males sing at the same time stimulates the synchronization of the ovulation of the females.

The fact that males sings at the same time produce the synchronization of the ovultion of females of humpback whale (Picture: Yellowmagpie).

REFERENCES

• Berta A, Sumich J & Kovacs KM (2006). Marine mammlas. Evolutionary biology. Ed. Academic Press (2 ed)
• Day (2008). Guía para observar ballenas, delfines y marsopas en su hábitat. Ed. Blume
• Perrin WF, Würsig B & Thewissen JGM (2009). Ed. Academic Press (2 ed)
• Reeves RR, Stewart BS, Clapham PJ & Powell JA (2005). Guía de los mamíferos marinos del mundo. Ed. Omega

Common names of Mysticeti

In this publication, there is a table that relate the scientific name of the different species of Mysticeti cetaceans (cetaceans with baleens) with their common names in Catalan, Spanish and English. You can observe that the most part of them have several names.

Nom científic	Català	Espanyol	Anglès
Nombre científico	Catalán	Español	Inglés
Scientific name	Catalan	Spanish	English
Eschrichtius gibbosus	Balena gris	Ballena gris	Gray whale
Caperea marginata	Balena franca pigmea	Ballena franca pigmea Ballena franca enana	Pygmy right whale
Balaenoptera musculus	Balena blava	Ballena azul Rorcual azul	Blue whale Sibbald’s Rorqual Suphur-bottom Whale Pygmy Blue Whale
Balaenoptera physalus	Rorqual comú	Rorcual común Ballena de aleta Ballena Boba	Fin whale Finback whale Fin-backed whale Finner Herring Whale Razorback Common rorqual
Megaptera novaeangliae	Iubarta Balena amb gep	Yubarta Gubarte Ballena jorobada Jorobada Rorcual jorobado	Humpback whale Hump whale Hunchbacked Whale Bunch
Balaenoptera borealis	Rorqual boreal	Rorcual boreal Rorcual norteño Rorcual de Rudolphi Rorcual sei Ballena boba Ballena sei	Sei whale Rudophi’s Rorqual Coalfish Whale Pollack Whale
Balaenoptera edeni	Rorqual tropical Rorqual de Bryde	Rorcual tropical Rorqual de Eden Rorqual enano Ballena de Bryde	Bryde’s Whale Tropical Whale Common Bryde’s Whale Eden’s Whale Pygmy Bryde’s Whale
Balaenoptera brydei	Rorqual de Bryde	Rorcual de Bryde Ballena de Bryde	Bryde’s Whale Tropical Whale Common Bryde’s Whale Eden’s Whale Pygmy Bryde’s Whale
Balaenoptera acutorostrata	Rorqual d’aleta blanca (Hemisferi nord)	Rorcual aliblanco Ballena de Minke común Ballena enana Rorcual menor	Common Minke Whale Northern Minke Whale Lesser Rorqual Little Piked Whale Dwarf Minke Whale
Balaenoptera bonaerensis	Rorqual d’aleta blanca (Hemisferi sud)	Rorcual austral Minke antártico	Antarctic Minke Whale Southern Minke Whale
Balaena mysticetus	Balena de Grenlàndia Balena franca àrtica	Ballena de Groenlàndia Ballena boreal	Greenland Right Whale Bowhead whale
Eubalaena glacialis	Balena franca glacial Balena franca comuna Balena basca	Ballena franca glacial Ballena de los vascos Ballena franca del norte Ballenga	North Atlantic Right Whale Northern Right Whale Right Whale Black Right Whale
Eubalaena australis	Balena franca austral	Ballena franca austral	Southern right whale
Eubalaena japonica	Balena franca del Pacífic Nord	Ballena franca del Pacífico Norte	North Pacific right whale