Did you know that approximately 9500 species of trees could potentially disappear in the near future? And the estimation is more realistically between 12000 and 20000 (of the 60000 of tree species described so far)! Tree biodiversity (or genetic diversity of trees) is essential because it ensures that trees can adapt to different environments and deal with changes and environmental stress, so the conservation of such diversity is vital.

Approximately 9500 species of trees could potentially disappear in the near future.

To share the latest information and discuss strategies for collaboration to conserve the genetic diversity of tree species, 120 scientists and conservation managers from different countries met in Chicago last spring. Kevin Potter (professor at North Carolina State University) is one of the authors of the introduction paper to the special issue dedicated to the Chicago meeting “Gene Conservation of Tree Species – Banking on the Future” (*), so we asked him to tell us about genetic diversity of trees and the meeting’s purposes and conclusions.

Why conservation matters?

Unlike animals, plants cannot move so they need to manage threats in a different way than running away; genetic diversity is the key to the ability of plants to adapt to changing conditions. Trees in particular, among the longest-living organisms on the planet, show in fact higher genetic variation within a single population than other kinds of plants.

Considering that we are facing a particularly tough time (we have entered an era of mass extinction in which the current extinction rate is at least three orders of magnitude -100 times- higher than Earth’s average across biological and geological history ) it is “imperative to effectively and efficiently conserve the world’s forest genetic resources”, Kevin says.

It is “imperative to effectively and efficiently conserve the world’s forest genetic resources”, Kevin says.

Trees can be conserved in their natural habitat (this is called in situ conservation, from Latin “at the place”) or somewhere else, where they would not necessarily grow (ex situ conservation, “outside the place”). National parks on one side and botanic gardens on the other are two main examples of these conservation approaches (Kew Gardens’ Millennium Seed Bank near London, UK, stores more than 2 billion seeds from ca. 37,400 plant species).

Some outcomes from the meeting

Still basic information about many tree species is greatly lacking, which is a major limitation to meet the global conservation targets set by the Global Strategy for Plant Conservation in 2002, in association with the international Convention for Biological Diversity. To achieve these targets, partnerships are essential. An evaluation of whether existing in situ reserves adequately protect species was also one of the subjects of the meeting, as well as the need to address key knowledge gaps about successful ex situ conservation methods and how to restore them in natural habitats (in fact a better coordination between ex situ and in situ was recommended). Most of the world’s tree genetic conservation efforts, have focused on temperate and boreal tree species, so great efforts are required for tropical and semi-tropical tree species, which show even higher diversity!

Another major challenge to the success of achieving the targets set by the GSPC is obviously the political choices of governments. The existential value of tree species is a hard sell (and Kevin ironically remarks “trees don’t vote!”). But on the bright side the meeting ended with a number of agreed collaborations among botanical gardens and governments (one example is between the US and Malawi for the conservation of Mulanje cedar, which has declined more than 90% in the past 30 years).

“Trees don’t vote!”

In conclusion

Forests have ecological, economic and cultural importance, and we must conserve their diversity; we have no choice (have a look at the FAO 2014 report on the State of World’s Forests Genetic Resources). Kevin ends the paper quoting leading tree conservation scientist Sir Peter Crane, who was a keynote speaker at the meeting: “There is plenty to be done, there is no time to lose, and as opportunities arise they need to be seized with vigour.” And those in Chicago last May definitely followed the advice and plan to continue doing so!”.

Read full article: Banking on the future: progress, challenges and opportunities for the genetic conservation of forest trees

(*) The meeting “Gene Conservation of Tree Species – Banking on the Future” was organized by the U.S. Forest Service and The Morton Arboretum, the Chicago Botanic Garden, Botanic Gardens Conservation International, the U.S. Agricultural Research Service, the Western Forestry and Conservation Association, the American Public Gardens Association, and the Global Trees Campaign.

Kevin M. Potter is a conservation geneticist and landscape ecologist who applies evolutionary ecology tools and concepts to better understand the response of tree species and communities to forest health threats. He is a research associate professor in the Department of Forestry and Environmental Resources at North Carolina State University (NCSU), and works closely with the Eastern Forest Environmental Threat Assessment Center of the U.S. Forest Service. When he is not working, he spends time with his three kids and his wife (an applied mathematician), and he enjoys playing guitar and hiking.

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Vertical greening

Contemporary architecture is increasingly focusing on vertical greening systems as a means to restore the environmental integrity of urban areas, biodiversity and sustainability. Vertical greening is the activity of greening the building envelope with all forms of vegetated wall surfaces (www.greenroofs.org) as with plants either rooted into the ground, in the wall itself or in modular panels attached to the façade. Vertical green can be classified as façade greening or living wall systems according to the growing method employed. The plant choice affects the aesthetical and functional aspects of a greened façade and many parameters have to be taken into account when choosing plant species for vertical greening systems.  These parameters include the supporting system type, microclimatic benefits, maintenance needs, biomass production, climate type, and environmental parameters, façade orientation and constraints within the urban area.

Contemporary architecture is increasingly focusing on vertical greening systems as a means to restore the environmental integrity of urban areas, biodiversity and sustainability.

Benefits of vertical greening systems

Applying vertical greening systems on both new and existing buildings can offer multiple environmental benefits and a sustainable approach in terms of energy saving, nutrients and water management and efficient preservation of edifices.

The ecological and environmental benefits of green roofs include the improvement of air quality, the reduction of pollution, increased biodiversity and reduction of the heat island effect in urban areas. Plant’s leaves collect and absorb fine dust particles and transform the carbon dioxide produced by traffic & heating into carbon hydrates and oxygen. The reduction of the heat island effect in urban areas occurs thanks to the lower amount of heat re-radiated by greened façades and humidity affected by the evapostranspiration caused by plants as compared to artificial surfaces. This process also allows indirectly saving considerable energy supplied to the building as the plants and the growing medium provide insulation and shade which can reduce energy needed for cooling, especially in the Mediterranean area.

Vertical greening systems can improve biodiversity as they create a habitat for microorganisms and also for smaller animals such as bees, bats, birds, etc. Green façades function in this context as a food source (insects) and as nesting or breeding opportunity.

Besides the above-mentioned benefits, green roofs and walls also provide economic advantages. Those relate to the real estate market, greater durability of buildings, and a better psychological state of citizens.

The presence of vegetation in urban areas might affect the economic value of buildings, increase property or rental prices due to the improved aesthetic aspects. Both green roofs and vertical greening systems reduce the frequency of maintenance interventions thanks to a protective action of leaves against negative effects of UV rays, temperature fluctuations, acid rain and air pollution on the underlying surfaces.

Still, vegetation and green areas are scarce in contemporary urban environments, where impervious surfaces i.e. traditional building materials, asphalt roads, etc. may cover more than 75% of the total area. It’s advisable that most of the cities’ surfaces are green because some of the environmental benefits of greening the building envelope only work if a large surface in the given area is greened.

Our research and the process tree

My research focuses on the effects of vertical greening systems on the building energy performance and in particular on ways to reduce the energy demand for air conditioning. I consider environmental and economic suitability and sustainability of various vertical greening systems because it appears that some vertical greening systems are more sustainable than others from an economic and environmental perspective.

To provide a full perspective on vertical greening systems, I and my co-workers have developed a process tree.

The greening systems’ design needs to take into account many aspects including the integration with the building envelope, a sustainable material choice, the environmental impact, and the symbiosis between the growing medium and the vegetation, the economics related to costs and potential savings due to possible reduction of energy needed for heating and cooling. To provide a full perspective on vertical greening systems, I and my co-workers have developed a process tree.  Our process tree makes it possible to incorporate and analyze the main parameters of vertical greening systems and to compare various climate and building characteristics such as technologies, materials, durability, dimensions, and plant species employed in the design process. Our aim is to increase our understanding of vertical greening systems, to promote their use, to make their application possible and to help avoiding damages and maintenance problems caused by inappropriate design.

Our next steps

More research is needed to quantify all the environmental benefits of vertical greening systems, especially air quality improvement and cooling capacity. For this reason, we, the Ecosystemics research group of the Polytechnic School of the University of Genoa, Architecture and Design Department, built a pilot project in Italy, the first green wall built in the city of Genova. A broad research project is focused on the monitoring of the National Institute of Social Insurance (INPS) Green Façade pilot project, which includes the analysis of environmental, economic and social benefits in the context of densely urbanized areas, especially those in the Mediterranean region.

Read full article: Vertical greening systems, a process tree for green façades and living walls

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WARNING: Do not ingest, toxic!

Poison frogs (family Dendrobatidae) are some of the most spectacularly colored members of the animal kingdom and like many other dangerous or toxic animals, including venomous coral snakes and stinging bees, their bright colors act as a signal that warns potential predators to stay away. This combination of “danger” plus bright coloration is called aposematism.

Poison frogs are some of the most spectacularly colored members of the animal kingdom.

Poison frogs get their name from their ability to accumulate toxins in their skin, which they acquire through their diet.  Some species’ toxins are so potent that indigenous groups in Central and South America used the skin secretions from these tiny frogs to coat the tips of the darts they used for hunting (hence the other common name for this group, the poison dart frogs).  In fact, poison frog toxins continue to be of use to humans today for understanding physiological processes like heart function and pain sensation. For the frogs, however, their toxicity needs only to teach its natural enemies not to bother attacking again, which is where the bright, warning coloration comes in handy.

Because the effectiveness of animal warning signals depends on a the ability of a predator who has had a bad experience with one individual to recognize and that signal when they see it again, theory suggests that all individuals of the aposematic species should look alike – the more consistent the warning signal, the easier it is for the predator to learn to avoid it.  However, in poison frogs and some other taxa where aposematism is common striking examples of warning color diversity can be found.

The strawberry poison frog example

The strawberry poison frog (Oophaga pumilio) provides a great example of this.  These thumbnail sized frogs come in almost every color of the rainbow and are especially variable in color in the Bocas del Toro Archipelago off the coast of Panama.  Research in our group has focused on uncovering how selection, both natural and sexual, might have contributed to the evolution of this amazing color diversity.

In this study, we took advantage of an area where two distinct color morphs of O. pumilio occur in the same population (one red and one yellow, but both with large black spots) to test for differences in survival and predator attack rates between color morphs and learn about the potential role of natural selection in shaping color diversity.  Because in most of the adjacent populations frogs of this species are red, we predicted that more predators would have learned to avoid attacking red frogs than yellow ones, leaving the much less common yellow morph more vulnerable to attack.

To test our predictions, we used a combination of approaches including the use of red and yellow soft clay model frogs, which preserve evidence of predator attacks, a mark-recapture study, which permits comparison of survival rates for red versus yellow frogs, and visual modeling, which allows us to ask whether the frogs’ colors, that appear very distinct to the human eye, are distinguishable by a suite of potential predators with different visual sensitivities.

Contrary to our expectations…

Our results surprised us!  Both approaches we used suggested that red and yellow frogs do equally well, despite the fact that these colors are predicted to be both distinguishable and conspicuous to a variety of potential predators.  These findings suggest that counter to what we would expect based on aposematism theory, predation is not constraining the coloration that these frogs can exhibit.  Instead, it appears that predators avoid both colors efficiently, even though yellow is rare.  Perhaps attacks on these island frogs are so few and far between that natural selection is not constraining the evolution of coloration? If so, perhaps the answer to why these frogs are so incredibly color diverse is tied to sexual selection, given that the mate preferences of this species are also influenced by color!

Read full article: No evidence for differential survival or predation between sympatric color morphs of an aposematic poison frog

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Why I am fascinated by barrier islands

I grew up in the arid southwestern United States, far from the ocean.  When I moved to Florida, I quickly learned to love barrier islands, which I found to be both exotic and beautiful.  I was working on St. George Island in the northern Gulf of Mexico in the late 1990’s with a postdoc, Gretchen LeBuhn, and we were both struck by the similarities between the islands and, oddly, southwestern deserts.   Plants from both islands and deserts are subject to very harsh conditions and affected by extremes in precipitation and temperature, with windblown and low-nutrient sandy soils.

Understanding barrier islands is very important for the ecology, conservation, and economy of coastal areas.

Further, the vegetation dynamics were similar, in that species abundances could change quickly and dramatically. Species could appear or disappear in different years or locations.  What made islands unique from deserts were tropical storms; I had two entire field season’s wiped out by tropical storms and was witness to the significant destruction on St. George Island by Hurricane Opal in 1995.

Studying barrier islands

Gretchen and I were fascinated by the “shifting mosaic” of different species changing in occurrence in different parts of the dunes across months and years. We thought about how to quantify these spatial and temporal patterns and concluded that a long-term study on the fairly large scale of dunes and troughs was required.  We devised replicate large plots using a simple grid system within each plot and were about to start our first census in 1998 when Hurricane Georges brought 3 m of storm surge and destroyed some of our plots. I re-established the plots in 1999 and we have sampled the plots annually ever since.

I must admit that our initial goal was to just satisfy our own curiosities, and that Gretchen and I didn’t know about the larger potential value of this research.  Barrier islands occur along many coastlines worldwide in areas prone to high disturbance from storms. Their coastal dunes protect inland areas, including both human habitation and natural resources such as seagrass, oyster beds, and salt marshes, all of which serve as nurseries for important fisheries.  Understanding barrier islands is very important for the ecology, conservation, and economy of coastal areas.

Their coastal dunes protect inland areas, including both human habitation and natural resources such as seagrass, oyster beds, and salt marshes, all of which serve as nurseries for important fisheries.

Sand dune communities have also been used in many classic studies in ecology, going back to Cowles work in the 1890s on succession.  In ecosystem ecology, barrier islands are interesting because of a dynamic tension between the shapes and positions of the dunes and the vegetation growing on them. The dune structure determines what plants will establish and grow, while the vegetation can control the stability and dynamics of the dunes; meanwhile, both dunes and the vegetation undergo succession as islands build.

The importance of long-term studies

Our paper in Plant Ecology with the first eight years of the census was important for documenting effects of hurricanes, while also showing that other, less obvious climate factors such as drought could have equally large effects.  Elise Gornish and Hannah Buckley helped develop the analyses, using some interesting approaches for using long-term ordination data that we took from a paper by Tadashi Fukami.  Gornish later went on to use the long-term data as the basis for a model of hurricane effects on barrier islands, as well as to develop methods for restoration of dunes following hurricane disturbances.

One reason why this study has been well cited is the dearth of similar long-term studies of sand dunes, especially in the Gulf of Mexico.  The data provided by long-term studies are absolutely necessary for understanding natural dynamics, as well as for understanding the effects of sudden (e.g. oil spill, hurricane) and more gradual (e.g., sea level rise) disturbances.  Long-term studies are easy to initiate, hard to maintain, and often require significant investment of time and energy before they provide any meaningful results.  Yet, long-term studies fill an important need and I encourage everyone to consider initiating or participating in such studies.

The best science is done with friends

Other than working at a beautiful site, one of the real pleasures I have derived from this study is gathering colleagues, friends, and students together each year to conduct the survey.  It takes more than 10 people to complete the census over two or three days each fall. Now, by 2016, this research program has contributed to eight publications, two Master’s Theses, and many undergraduate research projects, and is a component of a field course for our entering graduate students in Ecology and Evolution at Florida State University. Certain people have been critical for keeping this project going, including Elise Gornish, Abigail Pastore, Marina Lauck, and especially Alice Winn. The annual census always reminds me of the companionship and joie de vivre that attracted me to ecology in the first place.

Read full article: Climate and coastal dune vegetation: disturbance, recovery, and succession

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Antarctica’s leopard seals and their diet

Few predators have a more ferocious (or well earned) reputation than Antarctica’s leopard seals. Early researchers called them the “principal enemy of the penguins” and today many people know them best as the bad guy from Happy Feet. After ambushing their feathered prey, they hold it in their long curved teeth and thrash it at the water’s surface, tearing it into swallowable chunks of flesh.

But seabirds aren’t the only large animals on their menu. These big predators (which can reach over 3 m long and weight up to 500kg) also target other seals. Around 78% of adult crabeater seals living in the pack-ice bear long parallel scars on their backs; a badge of honour that marks those that survived leopard seal attacks in their youth. They also target fur seals and even young elephant seals, which they kill by piercing the braincase with their long canines during repeated bites to the head. In the whaling days, leopard seals were even seen scavenging whale carcasses.

But interestingly, rather than specialising solely on the large prey upon which their reputation is based, studies of their wild diet have also shown that leopard seals often eat smaller prey, in particular Antarctic Krill. The question is then, how does such a large toothy predator capture and eat such tiny prey?

To explore this we worked with with Casey and Sabine, two adult leopard seals from Taronga Zoo (Australia), where they were living in human care after being found as juvenile vagrants near Sydney a long way from their Antarctic home.

We presented the seals with small fish in a special feeding apparatus. The seals could see the fish through the sides of apparatus, but were unable to use their teeth to get hold of them because the fish were surrounded by the device. Instead, seals had to suck the fish out.

Suction feeding and the sieve

Suction feeding is where animals create lower pressure inside their mouths relative to the pressure around them (generally by retracting their tongue in mammals), causing any prey swimming in front of the mouth to be sucked in along with its surrounding water. The problem with suction feeding, though, is that animals then need to get rid of this extra water before they can swallow their catch. This is where leopard seals do something interesting.

After capturing the fish by suction, the leopard seals in our study closed their jaws and forced the water captured along with prey out via the sides of the mouth. Their flabby cheeks seemed to control the flow of water, and to exit the mouth, the water also had to pass between the seal’s trident-shaped cheek teeth. Any food captured by suction is therefore trapped behind the sieve formed by the leopard seal’s teeth.

In the wild, this feeding behaviour likely enables leopard seals to suck in a mouthful of krill-laden water, before expelling the excess water and swallowing the krill in bulk. This is similar to how baleen whales like blue whales feed, except that these use ‘engulfment’ or ‘lunging’ to capture prey inside the mouth before it is sieved, rather than suction. Watch the Video Here.

This all comes down to the shape of their highly specialised teeth. When pursuing large prey, like penguins, they use their long, sharp canines and robust front teeth to kill and break apart their catch by thrashing it at the water’s surface. But when they feed on krill or small fish, they use suction to capture prey inside their mouth, before sieving it from the seawater with their trident-shaped cheek teeth. The unique shape of their teeth allows leopard seals to feed efficiently at both the top and bottom of the Antarctic food web, increasing their feeding options and therefore, their chances of survival.

However, while we’ve now seen these behaviours displayed in captivity, we still haven’t observed them directly in the wild. Historically, this has been very difficult to do because of the challenges faced when observing these animals in their pack-ice habitat. But advances in research technology are now making it easier to study leopard seals in their own environment.

Future studies

Recently, Krause et al. (2015) used CRITTERCAM to film leopard seals while hunting for seals, penguins and fish. This study provides some amazing insights into how these animals find and capture their food, as well as how they interact with each other while fighting over food. Hopefully future studies can make use of these exciting new technologies to catch the first glimpses of leopard seals using suction and filter feeding to consume krill in the wild.

For more info check our our original study.

Read full article: Leopard seals (Hydrurga leptonyx) use suction and filter feeding when hunting small prey underwater.

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Why understanding the Caatinga?

The Brazilian semiarid northeast is characterized by having one of the highest population densities among the regions of the world that have similar environmental characteristics. As the area estimated at approximately 882,000 square kilometers, the region is home to around 18 million people and has a population density of 20 inhabitants per square kilometers.

Brazilian tropical dry forest, the Caatinga – called white forest by the Indians – is the least studied ecosystems in South America. This ecosystem contains more than three hundred endemic plant species and also some Latin America animals that are threatened with extinction. For years, woody plant species of this biome has been cut and burned to serve as energy for a population without access to alternative sources. At this time, less than 1% of the total area is protected by permanent reserves, and this is the lowest percentage among Brazilian ecosystems.

An anthropic pressure and adverse weather forecasts present a threat to the Caatinga, and force us to accelerate knowledge of this ecosystem through interdisciplinary studies.

Can Caatinga tolerate the current challenges?

The weather pattern of the Brazilian northeast region is a strong factor influencing the living conditions of plants in Caatinga. The Caatinga has two distinct seasons. These are the rainy season that lasts three to four months and the dry season for the remaining months of the year. It is expected that due to the global climate change, the length of the dry season will increase. If this prediction is confirmed the recovery of Caatinga’s degraded area will be very difficult and the future of Caatinga insecure.

Plants abilities to survive during the dry season

The good news is that as the knowledge of the Caatinga is advancing via an integrated approach of ecology, physiology and plant anatomy, we can see how fantastic the different mechanisms act jointly to help species tolerate environmental conditions in the semiarid environment.

Most of Caatinga’s species have as strategy to lose their leaves at the beginning of the dry season to protect against the water loss. However, some species have a set of features that enable the maintenance of their leaves during months of drought. Besides several biochemical adjustments, we also observe anatomical strategies. For example, arboreal species Cynophalla flexuosa, directed the majority of its pores, responsible for CO₂ uptake for photosynthesis and release of water vapor between the leaves and air and called stomata, to the bottom side of the leaf. Furthermore, it created a special wall surrounding each particular stomatal pore that forms a barrier against water loss. These anatomical adjustments help reducing the rate of water vapor loss from the Cynophalla flexuosa leaves and ultimately help to survive the dry season.

In my point of view we should make lots of efforts to better understand the plant physiological ecology of the Caatinga, promote its conservation, and this should be done in front of the need for intense anthropic use and climate change.

Read full article: Caatinga, the Brazilian dry tropical forest: can it tolerate climate changes?

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Why do we need bees?

Along with its contribution to crop production of approximately 35% of all food in the world, animal pollination also maintains viable populations of native plants and guarantees the viability of several agriculture enterprises throughout the world. Among all pollinators, bees are the most important ones, either because of their diversity ways of life or because of the species diversity itself. These insects are very important to agriculture because they increase the yield of different crop plants, such as coffee, tomato, and sunflower.

Why bees are in danger?

The conservation of this insect group is attracting a considerable public concern because human activities are believed to cause significant population decreases in several different bee species. The habitat loss and fragmentation caused by agriculture intensification, the increased use of chemical defenses and the introduction of foreigner parasites are believed to be the main causes of bee decreases worldwide. Additionally, synergetic interactions between all these issues are also believed to be causing the pollination crisis reported elsewhere. On the other hand, our dependency on bee-pollinated crops has significantly increased lately, and this may cause a pollination debt in the near future.

Our case study: landscape changes and Euglossini bees in Brazil

With the above problems in mind, we aimed to evaluate the effects of landscape changes in the populations of two Brazilian Euglossini bees, Eulaema nigrita Lepeletier and Eufriesea auriceps Friese. The Euglossini bees are endemic to the Neotropics, very diverse (~250 species were already described) and related to forested areas. The males of these bees have a peculiar behavior: they collect flower scents to allegedly improve their pheromones and attract the females. Specifically considering these two species, but mainly E. nigrita, they are very generalist species, being able to be very resistant to environmental changes. In fact, E. nigrita abundances were already reported to increase in occurrence of anthropogenic disturbances. Since this species pollinates several different plant species, we expected them (mostly E. nigrita) not being affected by the landscape changes in the Brazilian Cerrado. Additionally, as this biome is naturally an opened habitat that naturally favors these species. Therefore, we expected that their abundances would not be much affected by the landscape changes.

Given their biological and ecological features, we sampled these bees in several areas in the Brazilian Cerrado to evaluate whether their populations were being affected by landscape changes, such as habitat loss and fragmentation in this biome. We sampled from several landscapes in this Brazilian biome and also measured the amount of fragmentation within each landscape, in an attempt to relate such changes with the species abundances in each sampled landscape. As expected, both of these species did not show any response to different landscape metrics measured. Still, we believe that for Euglossini bees with small body sizes, landscape features may still pose as important determinants of population sizes in the Neotropical region.

Good news for Euglossini bees in Brazil but how about future?

Of course these results do not indicate there are no menaces to bees in the Brazilian Cerrado savanna. These results only indicate that both of these Euglossini species are well-adapted to the environmental changes induced by humans and, consequently, did not show too much responses to the landscape changes. However, considering Euglossini bees from both Atlantic and Amazonian regions, deforestation, fragmentation, and habitat loss are indicated as pervasive ecological issues to bees. Even though the Euglossini fauna within the Cerrado may provide some protection to animal-pollinated crops, agriculture intensification of the ongoing and increasing application of agrochemicals pose as important and significant threats to bees in general and are expected to greatly affect pollination debt in the future. Since even generalist species may be negatively affected by these threats, pollinators-friendly actions done by farmers in general within their lands (i.e. maintenance of natural vegetation to serve as refuges for the bees, decrease in the amount of chemicals used etc.) are expected to help bees to strive in their natural remaining habitats. Otherwise, bee population decreases throughout the world are expected to continue significantly affecting the pollination debt and the potential economic losses regarding insect-pollinated crops.

Read full article: No Evidence of Habitat Loss Affecting the Orchid Bees Eulaema nigrita Lepeletier and Eufriesea auriceps Friese (Apidae: Euglossini) in the Brazilian Cerrado Savanna

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The ecological role of sounds

Sounds are used by vocal animals to perform several vital functions: bats use active-produced ultrasounds to intercept flying preys and avoid obstacles, elephants beat the soil to produce infrasound waves to inform others groups of their presence. Male songbirds perform complex songs to attract females and to defend territories from competitors. Sounds may be used collectively by vocal animals like mammals, birds, frogs or insects to produce high informative choruses at dawn and dusk.

The investigation of the role of the sounds in the ecology of several groups of animals (from insects to whales and shrimps), either living in high mountains, in tropical forests or in deep oceanic waters, represents an important advancement for the knowledge of Earth diversity and complexity.

Ecoacoustics a novel ecological discipline

Ecoacoustics is a new entry between the disciplines that investigate the ecology of the natural systems. It was recognized as an independent branch of the ecology at the first Ecoacoustics Congress in Paris in 2014 and the International Society of Ecoacoustics (ISE) was established. Since 2014, the ISE has been growing and attracting hundreds of scientists from the entire world.

This advancement has been possible thanks to new theories about the cognitive mechanisms used by vocal animals to communicate and to track resources, e.g. the Ecofield hypothesis, Soundtope hypothesis, Acoustic community hypothesis, Ecoacoustic events model.

Sounds are used by vocal animals to perform several vital functions.

Technologies and passive recording

As field naturalist my interest on the sounds of nature dates back to the 70’s when just graduated was used to count birds based on their acoustic cues. However, despite the awareness that sound information is an essential part of the ecological complexity, I had to wait until year 2000 to have available autonomous field recorders that can set date, time of recording and some environmental parameters like temperature, humidity, luminosity and atmospheric pressure. Contemporarily, digital memories of great capacity (128 Gb) and Li-Ion rechargeable batteries have improved the efficiency of this tool that can autonomously operate for a long time.

Sounds may be used to identify species and to understand the dynamic of acoustic communities in areas like tropics or oceans where the identification of species remains highly problematic. The noninvasiveness of the passive recording and the possibility to make a post-processing analysis in lab offers new opportunities for a long-term researcher also in remote regions.

The EEDI model

Despite the recent improvements in the field of recording, the ecoacoustic approach still faces difficulties especially when managing big data from long-term monitoring investigations.

To overpass this serious difficulty, recently I’ve proposed a model called Ecoacoustic Event Detection and Identification (EEDI) for the analysis of big data based on the concept of the ecoacoustic events. The ecoacoustic events are defined as emergent sonic patterns that are recognized by individual species during the completion of a specific function.

EEDI is based on the idea that the combination of acoustic indices describes unique acoustic events like geophonies, technophonies or biophonies and their combination. EEDI is powered by the SoundscapeMeter 2.0 and is very easy to use.

EEDI allows handling hundreds of acoustic files in a very small amount of time. EEDI has been designed for an ecological analysis of data more than for species identification, although in many cases identification of some species is possible.

Ecoacoustic conservation

Ecoacoustics is a discipline that will help to monitoring our Earth ecosystems extending benefit also to the application to biodiversity assessment, nature conservation and management of protected areas. It represents a necessary tool to create a public awareness of the risk of several biophonies being masked by the intrusion of human technophonies. There is a growing empirical evidence of the negative effects of technophonic sounds on the ecology of vocal animals.

Despite the short story of ecoacoustics, this discipline offers many possibilities to scientists, practitioners, decision makers and politicians to improve the knowledge of our complex world. It seems to be especially important in tropical areas and in deep oceans where research is difficult and the risk of species extinction is very high and requires an urgent action.

Sound performances in many animals are vital traits to accomplish many strategic functions. If such biophonies are masked by unwanted sounds many species may disappear.

Thanks to ecoacoustics we have discovered that noise is a further threat produced by human intrusion to Earth ecosystems functioning and well-being.

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Jakob von Uexküll´s theory of meaning

In his introduction to Theory of Meaning (1940, published in English in Semiotica 1982), the German-Baltic biologist Jakob von Uexküll (1864–1944) refers to a prominent biologist who had criticized his Umwelt theory – a biological theory about the experiential worlds of animals – for being misleading in its depiction of an orderly arrangement of nature.

[This biologist] perceives nature´s countenance like a chemist confronting the Sistine Madonna. Although he can see the colors, he cannot see the picture. The chemist can certainly learn much by chemically analyzing the colors, but such an analysis is irrelevant to the painting.

As we see here, Uexküll compares his critic´s «meaning-blindness» to color-blindness. The subjective biology that Uexküll called for takes the perspective of the living being that is the subject of biological study. In order to understand for instance an animal, he reasoned, we must understand what carries meaning in its subjective, experiential world, its Umwelt.

The study of meaning in nature

Biosemiotics is the approach within today´s biology that most systematically advances  Uexküll´s point of view. The main idea of biosemiotics, as stated by its founding scholar Thomas A. Sebeok (1920–2001), is that life and semiosis are coextensive. Semiosis is sign exchange, exchange of signs – where “a sign” somehow stands for something else than itself.

Signs carry meaning. And life carries certain mind-like properties that enable meaningful interpretation of perceived signs. This outlook contrasts with the traditional dualistic approach in science that distinguishes sharply between mind and matter. Biosemiotics explores the gradual emergence of various qualities, including broad phenomena such as life and mind.

Biosemiotics explores the gradual emergence of various qualities, including broad phenomena such as life and mind.

The mind-like properties found elsewhere in nature can be very different from the human mind. Biosemiotics does not promote anthropomorphism – attribution of human traits to non-humans. Instead, it acknowledges the diversity of semiosis across and within the various levels of biological organization, from the cell via individuals to ecosystems.

Challenges

Sign processes are easily recognized in animals that communicate and learn, but it is more difficult to find similar processes in organisms without nerves and brains. Molecular biologists are used to talk about information transfer. While the animal itself interprets signs appearing in its perception, it is harder to say what it is in cells that interprets information.

The semiotic enterprise’s expansion to the entire tree of life is an enormous challenge. We have to admit that semiosis in simple bacteria is qualitatively different from the semiosis in advanced eukaryotic cells, and even more radically different from the brain-based semiosis of animals.

Semiosis evolved with life, and both gradually increased their complexity and organization. This process of evolution is not merely a quantitative affair, but a process paved with important qualitative inventions that at some points in time restructured both the nature of life and the character of signs.

Biosemiotic ideas about development and evolution

Uexküll was the first to propose that objects in the environment have specific meanings for different organisms. A key feature of biosemiotics is that it considers the workings of semiosis at multiple time scales, and emphasizes the active role organisms have in reshaping sign relations.

The healthy development – growing up, coming-to-be – of an organism presupposes that it is surrounded by an environment that is rich in terms of signs and meets its requirements. Only in a rich and suitable environment can an organism act by selecting what is meaningful to it, attribute meanings to environmental objects and develop its subjective world, its Umwelt.

The healthy development – growing up, coming-to-be – of an organism presupposes that it is surrounded by an environment that is rich in terms of signs and meets its requirements.

This holds true whether we are talking about human child development (where required elements include social caretakers and eventually companions) or the development of organisms in general.

Organisms are active in shaping their own lives. The active role of organisms has crucial implications for our understanding of ecological and evolutionary processes. By altering sign relations, organisms influence what they recognize and how they respond to it. Organisms also change sign relations in other species. In the big picture, we all affect each other.

Biosemiotics offers a new platform for explaining biological evolution. It says that evolution is semiosis, a process of continuous interpretation and re-interpretation of hereditary signs alongside other signs that originate in the environment or the body.

This blog post includes text drawn from three editorials published in Biosemiotics, all written by Alexei Sharov, Timo Maran and Morten Tønnessen: Towards Synthesis of Biology and Semiotics (2015), Organisms Reshape Sign Relations (2015) and Comprehending the Semiosis of Evolution (2016).

The journal Biosemiotics is the official periodical of the International Society for Biosemiotic Studies (ISBS), a society that organizes an annual International Gathering in Biosemiotics.

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When I saw a foot-flagging frog (a frog that waves his hind legs to show colored foot webbings) for the first time, I was standing on top of a waterfall in Borneo. I yelled out to my colleague: “they are down there” but he could not understand me, so I started signaling with my hands (look-down there). At this moment it became pretty clear why sound is often not enough to communicate in noisy environments, and for the rest of the day both of us watched male foot-flagging frogs defending their perching sites with acoustic and visual signals.

Environmental noise is of course not constricted to rushing water; a lot comes from other animals, for examples cicadas that sing to find a mate or other frog species that advertise to attract females and to repel rivals. Most of this noise is restricted to certain time periods or a certain frequency and frogs are experts in avoiding signal overlaps. However individuals of the same species have equal activity times, more or less the same call frequency, and like males of an Indian foot-flagging frog call from stones in noisy streams, which makes it difficult to detect your rivals.

But why signal in noisy environments in the first place? In the case of foot-flagging frogs, almost all species worldwide live and more importantly breed in fast-flowing stream habitats. The streams are visited by gravid females. Males perch along the stream and attend choruses; thereby increasing their chance to attract a mate. To deal with noise, they use additional visual modalities for communication.

A second signal modality

The approximately 2 cm large (or rather small) males of the Indian foot-flagging frog species inflate a bright white vocal sac while calling. And although their body coloration can vary from yellow, reddish or dark brown they are always very well camouflaged in their environment. Only while calling, when the white vocal sac flashes periodically or while foot-flagging and displaying silver foot-webbings, can one immediately visually detect them. The vocal sac did not evolve as a visual cue per se, but rather as an organ that recycles air while calling. This made us curious and we wanted to test if males are influenced by the visual signal of the pulsating vocal sac or rather react to only the calls of conspecifics.

So we used two plastic boxes that were glued on top of each other, the bottom was sunk in the stream and the on the top box we affixed the tip of a rubber glove connected to a tube we could manually inflate from a distance. Behind the top box we put a loudspeaker. We then played back only calls from a distance of 50 cm to a frog and later we tested the reaction of individual males to calls and the flashing rubber balloon. For our results we only used reactions displayed for a standardized period of 4 minutes after play back presentations. Just out of interest, we kept on playing multimodal presentations in some trials and some frogs did not get tired to compete with the rubber balloon mimicking the white vocal sac with accompanying call stimuli.

Our results suggested that visual signals of an inflating vocal sac are used to locate and detect the opponent and elicit more and longer calls and more visual signal activity in males than play-back calls alone. Interestingly, the tested males only displayed foot-flagging behavior in response to acoustic and visual stimuli. Thereby males that detected an opponent (in our case: calls from a loudspeaker and synchronously inflating balloon) in close vicinity immediately started advertising and signaled threat displays.

Foot-flagging behavior

Unlike the common assumption that foot-flagging frogs wave their legs and show their colored webbings to attract females, the influence of foot-flags on females has never been tested. Foot flagging is mainly used as an agonistic or threat signal towards rivals and most likely originates from a kicking behavior to kick the opponent off its perching site and claim the territory. Exaggerations of limb lifting and stereotype movement patterns causing a behavioral change in opponents could have triggered the ritualization of the conspicuous foot-flagging behavior.

The threat signals are also used by juveniles of a Bornean species during feeding in the Vienna Zoo presumably to defend food resources. Our recent investigations showed that androgenic hormones mediate the behavior and androgen receptors in the hind limb musculature are expressed at levels 10x greater than in two other anuran species that do not produce foot signals.

Whenever you ask somebody how frogs communicate, the answer will be: “ribbit ribbit”! Vocalizations are the most conspicuous displays to human observers and as a consequence other signal modalities have traditionally received less attention. However over the past decades we have realized that colors and movements fulfill communicative functions and help frogs to deal with biotic and abiotic noise, an important accessory in an increasingly noisy world.

Read full journal article: Multimodal signaling in the Small Torrent Frog (Micrixalus saxicola) in a complex acoustic environment

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