Habitat loss is bad news for species – especially for top predators

Scientists at Linkoping University, Sweden, have simulated what happens in ecosystems when the habitats of different species disappear. When plants and animals lose their habitats, predator species at the top of the food chain die out first. The results have been published in Ecology Letters, and may provide information for and strengthen initiatives to preserve biodiversity.

Credit: Nagel Photography/Shutterstock

One of the most serious threats against biodiversity is habitat loss. Humans cause severe changes in the landscapes when converting or removing natural land to be used for construction or food production. In addition, climate change is also causing some regions to become uninhabitable for some species. Researchers at Linkoping University have developed a mathematical method to investigate how large ecosystems are affected when habitat disappears.

"We can reach two important conclusions from our study. The first is that initiatives to preserve biological diversity must preserve habitat and not only focus on a particular species. It is very important to consider the interactions between the ecosystem's species by looking at the food web—which animals and plants are eaten by which other animals. The second conclusion is that the order in which habitats disappear has a profound significance," says Anna Eklof, senior lecturer in the Department of Physics, Chemistry and Biology (IFM) at Linkoping University.

The LiU researchers use modeling and computer simulations to study ecological networks, which describe how the various species in an ecosystem interact. The article, published in Ecology Letters, combines two mathematical models: a classical and a new one. The model described in the article distinguishes between suitable habitats in which species can live, and other areas in which they cannot. Suitable habitat patches are distributed across the landscape, with different plant and animal species spread across them. The species are connected to each other in a food web, a network that describes how they feed on each other. A hare eats several types of plants, the hare and several other prey species can become food for foxes, and the fox is one of the predators at the top of the food web.

The survival of an animal in a particular habitat depends on having the correct prey animals or plants in the same habitat patch. The model developed by the researchers also considers how effectively species can move between the habitat patches. In the real world, the habitat patches are often separated by inhospitable regions, such as a road with heavy traffic, that can prevent plants and animals from moving between them. If dispersal between different habitat patches becomes more difficult, probability increases that a species becomes extinct in the ecological network—which in turn influences the survival of other species.

 

The researchers have used the model to analyze a large number of simulated networks involving several hundreds of species. They also tested the model on a dataset of measurements describing the food web of the Serengeti National Park in Tanzania. In order to investigate how ecosystems are affected by habitat loss, the researchers ranked the habitat patches in order of how important they are for species at the bottom of the food chain. They then simulated three different ways in which habitat loss can occur: with the least important habitat patches removed first, the most important ones first, or removing them in a random order. The destruction of habitat in a random order is similar to what happens when humans construct roads or buildings without considering how valuable the region is for different species.

"In our model, the species at the upper levels of the food chain die out first when habitat patches are lost. What surprised us was that the damage to the ecosystem was almost the same when patches were lost in a random order as when the most valuable patches were lost first," says research fellow Gyorgy Barabas.

The researchers emphasize that it is important to classify how significant various habitats patches are when considering initiatives to preserve ecosystems, and to give priority to the most valuable ones. The resilience of the ecosystem to species extinctions can also be improved by, for example, strengthening connections between patches. By taking such matters into consideration when determining how land is used, humans can protect ecosystems and prevent species from becoming extinct—particularly species that are high up in the food chain.

Author: Karin Soderlund Leifler | Source: Linkoping University [October 28, 2020]

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Leaving more big fish in the sea reduces CO2 emissions

An international team of scientists has found leaving more big fish in the sea reduces the amount of carbon dioxide (CO2) released into the Earth's atmosphere.

Leaving more big fish in the sea--especially where fishing is not economically profitable in the
Central Pacific, South Atlantic, and North Indian Oceans --reduces the amount of
carbon dioxide (CO2) released into the Earth's atmosphere [Credit: Enric Sala]

When a fish dies in the ocean it sinks to the depths, sequestrating all the carbon it contains with it. This is a form of 'blue carbon'--carbon captured and stored by the world's ocean and coastal ecosystems.

"But when a fish is caught, the carbon it contains is partly emitted into the atmosphere as CO2 a few days or weeks after," said Gael Mariani, a PhD student at the University of Montpellier in France.

Mr Mariani led a world-first study showing how ocean fisheries have released at least 730 million metric tons of CO2 into the atmosphere since 1950. An estimated 20.4 million metric tons of CO2 was emitted in 2014--equivalent to the annual emissions of 4.5 million cars.

Co-author Professor David Mouillot from the ARC Centre of Excellence for Coral Reef Studies at James Cook University (CoralCoE at JCU) and the University of Montpellier said the carbon footprint of fisheries is 25 percent higher than previous industry estimates.

"Fishing boats produce greenhouse gases by consuming fuel," Prof Mouillot said. "And now we know that extracting fish releases additional CO2 that would otherwise remain captive in the ocean."

Large fish such as tuna, sharks, mackerel and swordfish are about 10 to 15 percent carbon.

"When these fish die, they sink rapidly," Prof Mouillot said. "As a result, most of the carbon they contain is sequestered at the bottom of the sea for thousands or even millions of years. They are therefore carbon sinks--the size of which has never been estimated before."

He says this natural phenomenon--a blue carbon pump--has been increasingly and greatly disrupted by industrial fishing.

The authors also say the phenomenon has not only been overlooked until now, but it happens in areas where fishing is not economically profitable: in the Central Pacific, South Atlantic, and North Indian Oceans.

"Fishing boats sometimes go to very remote areas--with enormous fuel consumption--even though the fish caught in these areas are not profitable and fishing is only viable thanks to subsidies," Mr Mariani said.

For the authors of the study, the new data strongly supports more reasoned fishing.

"The annihilation of the blue carbon pump represented by large fish suggests new protection and management measures must be put in place, so that more large fish can remain a carbon sink and no longer become an additional CO2 source," Mr Mariani said. "And in doing so we further reduce CO2 emissions by burning less fuel."

"We need to fish better," Prof Mouillot said.

The study is published in Science Advances.

Source: ARC Centre of Excellence for Coral Reef Studies [October 28, 2020]

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Tracking the Himalayan history from the evolution of hundreds of frogs, lizards and snakes

The Himalaya are among the youngest and highest mountains in the world, but the exact timing of their uplift and origins of their biodiversity are still in debate. Generally, there are two hypotheses about the uplift process of the Himalaya. The "Stepwise Hypothesis" states that the Himalaya rose slowly from 1000-2500 m during 56-23 million years ago (Ma), before an additional rapid uplift to 4000 m during 23-19 Ma, and a final rise to the current average elevations (~5000 m) at around 15 Ma. Alternatively, recent hydrological and thermal evidences support that this region was probably not elevated to current elevation till mid-Pliocene ("Late Orogeny Hypothesis").

The Himalaya and representative amphibians and reptiles
[Credit: Science China Press]

Time-based records of biological processes can be informative about montane histories and environmental changes. Various hypotheses about Himalayan origins can be tested using phylogenetic information and estimates of the timing of biological speciation events. To address the question about the timing of the Himalaya uplift, we carried out field work across the Himalaya to collect samples of amphibians and reptiles. The Himalayan region encompasses multiple countries and has many access challenges, so sampling across the entire region is difficult, which has inhibited integrative studies of the origin of the Himalayan biota.

Combining 14 time-calibrated phylogenies of Himalayan-associated amphibian and reptile families involving 85 genera and 1628 species, we estimated times of divergence among 183 species that occur in the Himalaya. We identified 230 biogeographic events related to the Himalayan species. The dynamics of in situ diversification and dispersal rates remained essentially parallel across the Cenozoic. Both the in situ diversification rate, as well as the dispersal rate into the Himalaya, fit the Stepwise Hypothesis for the origin of this mountain range. In contrast, our estimates of origination and peak diversification are not consistent with the late-uplift hypothesis.

Biotic assembly through time of herpetofauna in the Himalaya. (a): The rates of in situ diversification
 and dispersal of the Himalayan herpetofauna through time (smoothed across 5 Ma windows).
Dispersal indicates "dispersal into the Himalaya." MDivE = maximal number of observed
 in situ diversification events per Ma. MDisE = maximal number of observed dispersal events
per Ma. Ambiguous events are separately listed. (b): Dispersal events from adjacent regions
 into the Himalaya (smoothed across 5 Ma windows). MDisE = maximal number
of observed dispersal events per Ma [Credit: Science China Press]

The rapid Himalayan uplift and associated intensified South Asia Monsoon not only promoted a pulse of uplift-driven in situ diversification, but also affected the rates of biotic interchange. Biotic interchange was restricted by the lack of a moist environment that is required by many reptiles and amphibians. In contrast, an expanded tropical forest belt is thought to have persisted between the Himalaya and Southeast Asia since the middle Miocene, which likely accounts for the high dispersal rates between these two regions.

This work has important implications about the assembly process of Himalayan herpetofauna and its conservation. Our analyses show a deep-rooted origin of Himalayan herpetofauna originating in the Paleocene, but with rapid diversification in the Miocene.

The study is published in the National Science Review 2020.

Source: South China Press [October 26, 2020]

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Hidden losses deep in the Amazon rainforest

Few places on Earth are as rich in biodiversity and removed from human influence as the world's largest rainforest -- the Amazon. Scientists at Louisiana State University (LSU) have been conducting research within the pristine rainforest for decades. However, they began to notice that some of the animals, specifically birds that forage on and near the forest floor, had become very difficult to find.

New research shows animal patterns are changing in the absence of landscape change, which signals
a sobering warning that simply preserving forests will not maintain rainforest biodiversity
[Credit: Vitek Jirinec, LSU]

"What we think is happening is an erosion of biodiversity, a loss of some of the richness in a place where we would hope biodiversity can be maintained," said LSU School of Renewable Natural Resources Professor Philip Stouffer, who is the lead author of a new study published in Ecology Letters.

Stouffer began leading field research deep within the Amazon rainforest, north of Manaus, Brazil, when he was a post-doctoral researcher with the Smithsonian in 1991. With support from the National Science Foundation, he continued to oversee bird monitoring at the Biological Dynamics of Forest Fragments Project until 2016. However, around 2008, he and his graduate students noticed that they could seldom find some bird species that they had observed in previous years.

Stouffer and his students devised a research plan to collect new data that would be directly comparable to historical samples from the early 1980s. LSU graduate students Vitek Jirinec and Cameron Rutt collaborated with Stouffer to synthesize the results, aided by the computational modeling expertise from co-author LSU Department of Oceanography & Coastal Sciences Assistant Professor Stephen Midway. The team analyzed the vast dataset that spanned more than 35 years and covered 55 sites to investigate what Stouffer and his graduate students had observed in the field.

"It's a very robust dataset from a variety of places collected over many years. It's not just some fluke. It looks like there's a real pattern and it looks like it could be linked to things we know are happening with global climate change that are affecting even this pristine place," Midway said.

This downward trend signals a shifting baseline that could have gone undetected.

"Our nostalgia was correct--certain birds are much less common than they used to be," Stouffer said. "If animal patterns are changing in the absence of landscape change, it signals a sobering warning that simply preserving forests will not maintain rainforest biodiversity."

Winners and losers

In general, the birds that have experienced the most dramatic declines live on or near the forest floor where they forage on arthropods, mostly insects. However, there is some variation among species winners and losers in the rainforest.

The iconic voice of the Amazon rainforest, the Musician Wren, is one of the birds that researchers
have discovered is on the decline in pristine, remote parts of the Amazon
[Credit: Philip Stouffer, LSU]

For example, the Wing-banded Antbird , or Myrmornis torquata, is one of the species that has declined since the 1980s. It is also one of the species that forages insects on the forest floor by searching under leaves and other debris. Also declining is the Musician Wren , or Cyphorinus arada, a seldom-seen bird with one of the iconic voices of the Amazon.

Conversely, the White-plumed Antbird , or Pithys albifrons, has not declined and remains common. Its foraging strategy may be the key to its resilience. The White-plumed Antbird follows swarms of marauding ants that churn up other insects hidden on the forest floor. The antbird jockeys for an advantageous position ahead of the ant swarm and preys upon the fleeing insects. The White-plumed Antbird is not tied to one location in the rainforest. It travels and eats a variety of prey surfaced by the swarms of ants.

The scientists also found that frugivores, or birds that also eat fruit, are increasing in abundance. This suggests that omnivorous birds with more flexible diets can adjust to changing environmental conditions.

More research is needed to better understand the hidden losses and shifting baseline that are happening in the Amazon rainforest and other parts of the planet. "The idea that things are changing, even in the most pristine parts of our planet yet we don't even know it, illustrates the need for us to pay more attention," Stouffer said.

Source: Louisiana State University [October 26, 2020]

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