Blog written by Cameron L. Rutt, PhD Candidate at Louisiana State University, USA. Read the full paper here. 

Recent forest fires throughout the Brazilian Amazon’s southern tier have reignited the international consciousness, bringing renewed focus to the wake left behind by the blazes—deforestation. But, this is not a new phenomenon in the world’s largest rainforest, especially along the so-called “arc of deforestation,” in the Brazilian Amazon’s southern and southeastern reaches. Over the past 30 years, deforestation practices across this entire region have carved a California-sized hole in this once seamless forest, adding to the now 20% that has been clearcut.

Large clearings for agriculture and cattle ranches stand in stark contrast to the surrounding forested areas, which teem with rich plant and animal communities. We now have decades of research following deforestation that illustrate in sobering detail just how devastating habitat loss is for the unique forest biodiversity. But we also need to learn about the kinds of species that colonize and tolerate these human-modified landscapes. What is the legacy of these newly cultivated habitats?

The first question this begs is one of duration—does it take decades for animals to find and colonize these new areas of disturbance? A large-scale experiment in the central Amazon that once housed three cattle ranches helps us to answer that question for birds. Now largely abandoned by ranchers, scientists have been cataloging birds at the Biological Dynamics of Forest Fragments Project, for nearly 40 years.

We used these uniquely rich bird inventories to ask a series of simple questions. When an area is clearcut, do adjacent forest birds move in? If not, what habitat supplies the new arrivals? How quickly do they find these cracks in the Amazon? And how long do these novel avian communities linger? We found that there are dozens of outside species such as flycatchers and tanagers that almost immediately filled these anthropogenic cracks in the forest, even in the absence of large-scale transformation of the landscape.

In all, more than 100 bird species appeared that are not typically found in the surrounding pristine rainforest, and about three dozen of these established small populations within the disturbances. Moreover, these birds arrived quickly—the vast majority appeared within the first decade after the ranches’ establishment. Finally, a disproportionate number of these birds are widespread generalists, species that are commonly found in close association with humans. This includes birds regularly encountered in the largest Amazonian city of Manaus and species that frequent regional backyards and gardens.

This study also serves as an important benchmark to describe what happens when the landscape begins to heal. We found that as the forest recovers on the abandoned cattle ranches, these widespread birds began to retreat and disappear from the landscape because they were restricted to the disturbances. This is good news for the many specialized forest birds that can now regain lost habitat, but which could not survive in pastures or clearcuts. Therefore, for the health of the Amazon rainforest, we should minimize the intensity of human land-use and, should deforestation occur, allow the forest to reassert itself as soon as possible.

Deforestation rates in the Amazon are once again on the rise, further degrading the habitat of hundreds of species of birds. It is therefore critical that conservationists understand how these organisms, as well as the novel communities of widespread generalists, are coping with these large-scale landscape changes. Only then will we be able to develop best management practices for these impoverished habitats. Although this summer’s headline-grabbing fires in Brazil have ratcheted up the pressure for policymakers to stem the tide of Amazonian deforestation, we shouldn’t wait for another severe burning season to flame our interest and outrage about the state of the world’s most diverse forest.   

This work would not be possible without support from the Biological Dynamics of Forest Fragments Project and funding by the US National Science Foundation (LTREB 0545491 and 1257340).

Blog written by Suzanne Austin & Doug Robinson. Read the full paper here.

Why do lowland tropical birds have longer incubation periods than temperate species? This question has received substantial attention in recent decades with a large amount of research on a hypothesis known as the predation paradox. This hypothesis suggests that the longer tropical incubation periods are a consequence of parents reducing their own time at the nest to reduce chances predators will find the nests by seeing the parents coming and going. Nests of tropical songbirds are, on average, lost to predators more often and more quickly than those of temperate songbirds. For example, an average songbird nesting in the humid lowlands of Panama will have to nest about four times before they fledge offspring whereas a typical temperate songbird may need to nest only once or twice to fledge kids.

As a consequence of less parental time at the nest, egg temperatures drop, which then increases the time required for embryos to develop. Despite these ideas, there have been few data gathered on actual time spent incubating by most species of tropical birds. We documented incubation behavior by 112 species of tropical and temperate songbirds with video cameras plus some data from the existing literature.

To understand how adults were allocating time to incubation of eggs, we compared multiple variables that described adult incubation behavior including constancy (the total proportion of time that adults spend incubating), visit rate (the number of trips by parents to the nest in an hour), on-bout length (the amount of time parents spent incubating their eggs in an individual visit), and off-bout length (the time parents spent off of the eggs during an individual recess). We also compared each parental attendance variable to a set of environmental, natural history and life-history characteristics, such as nest predation rate, egg mass, adult mass, clutch size, adult incubation strategy (uni-parental or bi-parental), nest height, and nest type (open-cup, enclosed-cup, or cavity).

Despite longer tropical incubation periods, we found that the proportion of time (constancy) spent incubating was not different for tropical and temperate birds.  When we adjusted constancy to reflect the differences in day length between Michigan and Panama, we still found no difference associated with latitude in constancy. This result indicates that birds were spending a similar proportion of time incubating regardless of latitude (median= 71-75%).

However, when we investigated how birds allocated their incubation time, we found that tropical songbirds typically stayed longer on their eggs during each incubation bout (on-bout length), took longer recesses away from their eggs (off-bout length) and made fewer trips to their nests (visit rate). Lowland tropical species were engaging in a different incubation strategy than temperate songbirds.

While our finding of similar constancy across latitudes was inconsistent with the predation paradox, our data indicated that visit rate and off-bout length followed the pattern predicted by the predation paradox, but on-bout length didn’t. The expectation of lower constancy and shorter on-bout length, which were proposed to explain the longer tropical incubation periods, did not occur in our sample of tropical birds.  

Our data did reveal that nest predation was related to several attendance variables, but in directions inconsistent with those suggested by the predation paradox. Instead, birds subject to higher nest predation rate tended to spend more time on the nest rather than less time. We also found that incubation period was not related to any of our attendance variables, which suggests that how eggs were incubated didn’t explain the variation in incubation period length in the songbird species in our dataset.

We suggest that parents have optimized their incubation strategy to limit fitness costs to their offspring and to themselves, which may explain why constancy is fairly consistent within species. Yet, how birds allocate their time incubating their eggs varies across latitude. We suggest that there is an interaction between the environment and the needs of the embryo, which influences the strategy parents use to incubate their eggs. For example, the higher, more stable ambient temperatures of the lowland tropics likely allow parents to spend longer away from their eggs than temperate parents because the cooling rate of eggs is lower. These data add to the growing body of literature that suggests nest predation does not explain the observed differences in embryonic development across latitudes. Instead, much of the variation might be influenced by intrinsic differences in embryos during development, such as latitudinal differences in construction of immune systems, morphological attributes and degree of maturity at hatch.

Blog written by Karolína Brandlová. Read the full paper here.

It’s amazing to see my students getting their education in Prague, professionally growing and becoming part of the research and conservation teams across Africa. Our faculty is a sort of surprise, being situated in the heart of Europe and focused on tropical regions – Faculty of Tropical AgriSciences of the Czech University of Life Sciences Prague.

When I graduated (decades ago) our faculty was almost fully oriented to agriculture in the tropics. Fifteen years ago, we decided together with my colleagues concerned about wildlife to open a new study branch focused on wildlife management, currently named Wild and Domestic Animal Production, Management and Conservation. Step by step we have developed a team able to combine extensive fieldwork across Africa with teaching specific subjects focused both on wildlife management and conservation and on sustainable animal production. We’ve always been teaching in English and have acquired students from different parts of the world, passionate to join our projects and become wildlife management and conservation professionals. The first author of this paper, Mathias D’haen, is one of them.

He came to Prague from Belgium, with a clear idea to work on a conservation project in Africa. It was not easy at the very beginning to find a place where he could go to fulfil his idea for his master thesis, with results which would have clear applied conservation impact. He finally decided to join the team at African Parks, managing the extremely challenging Garamba National Park in the Democratic Republic of Congo, where he spent a year as a trainee and became responsible for giraffe research, monitoring and conservation.

Garamba National Park is really remote. The last remnant of a once widespread Kordofan giraffe population is now completely isolated, with the nearest neighbouring population hundreds of kilometres away in South Sudan – and it is unsure if those giraffe even still exist there . Garamba is also the southernmost part of the Kordofan giraffe area of distribution, with considerably higher humidity than the rest of its range, resulting in different vegetation conditions and composition.

Mathias became part of the team and, supported by experts from Giraffe Conservation Foundation, searched for answers to many crucial questions which may help set up effective conservation measures for this population. How many giraffe are, in fact, in Garamba? Where do they live and how they use the challenging environment? What should be done to ensure their long-term survival?

You can find some of the answers in the paper, and also some more questions which emerged during the data processing and result interpretation. We are all aware of the fact that the paper itself will not save the giraffe. However, the results of our study can be used to design dedicated conservation actions and make informed decisions. I am proud of Mathias who is still working with African Parks, and proud of many other students who are becoming conservation professionals able to conduct sound research which may be applied to effectively protect species and prevent species extinctions.

Blog written by Angela M. Mech, Matthew P. Ayres, and Daniel A. Herms. Read the full paper here.  

When we hear the word ‘Alien’, most of us conjure up images of extraterrestrials: terrifying, sharp-toothed, drooling, ugly creatures from outer space that are out to destroy us. The truth of the matter is that our fear regarding these aliens is not completely irrational – we don’t know what they would want, we don’t know how dangerous they could be, and we don’t know if we have any weapons that could stop them if they did turn out to be dangerous. When it comes to alien (non-native) herbivorous insects, we have the same fears for the same reasons. We don’t know if they will wipe out our native plants or permanently alter our ecosystems, we don’t know how much they will cost us, and we don’t know if we’ll be able to stop them. This fear exists even though we know that only a small percentage (~15%) of non-native insects actually damage our forests. One of the greatest challenges we face is that we don’t know whether a newly established insect will be harmless or a high-impact invader that causes widespread tree mortality. Our fears may be alleviated if we could somehow predict how much damage a non-native insect would cause before it even gets here. Towards that end, we need to understand what factors drive insect impact. In other words, what ingredients are in the recipe for destruction?

Approximately 450 non-native herbivorous insects have established in North American forests (Aukema et al. 2010). Since the late 1800’s, researchers have been trying to find a recipe that predicts their impact, with most hypotheses assuming that evolutionary history is probably one of the main ingredients. In our study, we evaluated multiple ingredients as potential predictors of insect impact, including those related to the evolutionary relationships between insects and trees. We examined four main categories: 1) insect traits such as the number of eggs laid, feeding method, and reproductive strategy; 2) host traits such as tree growth rate, wood density, and shade tolerance; 3) evolutionary history between the novel and coevolved hosts (i.e., how many million years ago the non-native insect’s new host and native host shared a common ancestor), and; 4) evolutionary history between the non-native insect and the species that coevolved with the new host tree (i.e., what is the closest insect relative that coevolved with the novel host?).

For our study, we focused on non-native insects that feed exclusively on conifer trees (conifer specialists). Conifers made a good model system because they are well studied (including evolutionary history) and of great importance ecologically and economically; 58 non-native insects in North America are considered conifer specialists. We found that divergence time to the most recent common ancestor between the insect’s native and new conifer host was a strong predictor of insect impact. For example, sap-feeding conifer specialists are more damaging on trees that diverged ~12-17 million years ago, with a 27% chance that they will cause widespread tree mortality, but that probability drops to as low as 1 in 650 million as the trees become more distantly related. In regards to host traits, we found that trees that were both shade tolerant and drought intolerant have a higher chance of experiencing mortality from a non-native insect than trees without these traits (26% versus 1.4% respectively). We also found that the chances of the non-native insect causing high impact was ten times lower if there was a North American insect in the same genus already utilizing the host tree. Surprisingly, there was no relationship between insect traits, singularly or in combination, and the probability that a non-native insect would be high-impact. Our research is the first that we know of to quantify the risk that a non-native insect will become a high-impact pest based on evolutionary history.

Most recipes typically have more than one ingredient, and we hypothesized that the same was probably true with predicting impact. In fact, we found that combining the three predictive models into a single model increased the strength of predictability beyond any of the individual models. From random selections of insect species that were high impact and not high impact, our composite model correctly identified the high-impact species 91% of the time. For example, one of the most damaging non-native conifer specialists in North America is the balsam woolly adelgid (Adelges piceae), which is causing mortality of a number of native fir species. These insect-tree combinations have the following category traits: 1) North American fir trees are shade tolerant and drought intolerant, 2) North American fir trees diverged from the European silver fir 13.6 – 16.8 million years ago, and 3) none of the North American fir trees coevolved with an Adelges species; the perfect recipe for mass destruction.

Our model provides a practical means for managing environmental security in the age of globalization. We can now better predict the impact that a non-native forest insect would have before it invades North America. Specifically, our combined model predicts whether a non-native, conifer specialist insect will have a one in 6.5 to a one in 2,858 chance of becoming high impact. This could have practical value in our struggles to limit high-impact non-native invasions. For example, we can now produce more quantitative and reliable watch lists of potential new pests, which could let us prevent their arrival in the first place. This knowledge will hopefully be a powerful weapon to help keep the next high-impact alien insect from becoming our next nightmare.  

Literature Cited

Aukema, J. E., McCullough, D. G., Von Holle, B., Liebhold, A., Britton, K., & Frankel, S. J. (2010). Historical accumulation of nonindigenous forest pests in the continental United States. Bioscience,60, 886-89. doi: 10.1525/bio.2010.60.11.5