Seed consumption by rodents reflects the signature of top-down effects mediated by wolves

Blog written by Jennifer L. Chandler and John L. Orrock. Read the full paper here.

Because most plants die before becoming seedlings, the distribution and abundance of plants often depends upon the distribution and survival of plant seeds. Small mammals are ubiquitous granivores with the potential to determine the distribution and regeneration of plants and trees in forests. Despite their importance, patterns of rodent granivory can also be highly variable, making it difficult to predict how granivory will affect plant recruitment at large scales. While variation in productivity, seasonality, or latitude have been identified as important for predicting patterns of seed predation, often considerable variation in seed predation exists even after these factors are considered.

Since rodents are common prey of carnivores, knowledge of activity patterns of rodent predators may play a part in predicting hotspots and coldspots of seed consumption by rodents. Large carnivores can have effects that cascade down the food chain, altering ecosystem dynamics both when they are removed and reintroduced to a system. Top carnivores can affect abundance and behavior of mesocarnivores, which in turn affect abundance and behavior of their prey, usually herbivores, which can alter plant abundance and community composition. We hypothesized that distributions of apex predators can create large-scale variation in the distribution and abundance of mesopredators that consume small mammals, creating predictable areas of high and low seed survival.

The hypothesized effects of interactions among carnivores on rodent abundance and seed survival. Solid arrows represent direct effects and dashed arrows represent indirect effects. Pluses and minuses indicate positive and negative effects.

The natural recolonization of northern Wisconsin by gray wolves (Canis lupus) presented a unique opportunity to test the hypothesis that interactions among carnivores affect seed consumption by rodents. By comparing areas recolonized by wolves to areas that had been essentially wolf-free since 1960, we could test whether apex predator presence indicates areas of low seed predation by rodents. Gray wolves competitively exclude coyotes (C. latrans), but better tolerate foxes (Vulpes vulpes, Urocyon cinereoargentus) because foxes have less diet overlap with wolves and are therefore, are less competition. Thus, areas with high wolf activity, such as wolf territories, are areas of relatively lower coyote activity, and higher fox activity. Foxes are expected to consume a greater proportion of small mammals, such as rodents that eat seeds, compared to coyotes. Consequently, we hypothesized that wolf territories may be areas of lower seed consumption due to the higher abundance of rodent predators.

Using multi-year field trials at sites inside and outside of 11 wolf territories in northern Wisconsin, USA, we evaluated whether rodent abundance and seed consumption were lower in wolf territories. At each site, we conducted live trapping sessions to survey rodent abundance. To measure seed consumption, we placed seed depots (plastic containers with known numbers of seeds of four tree species scattered on top of a layer of sand) at study locations for two-week periods, after which, seeds depots were collected and remaining seeds were counted. To confirm that differences between areas inside and outside of wolf territories were a result of differing interactions among carnivores, we also investigated several alternate explanations for the patterns in rodent abundance and seed survival that we observed. We measured a variety of habitat characteristics across our site, such as tree canopy cover, shrub cover, and presence of woody debris (all factors that can influence rodent abundance and activity), to rule out other potential causes of low rodent abundance and seed consumption that may be inherent in habitat where wolves preferentially establish territories.

Acer saccharum and A. rubrum seeds consumed by small mammals inside a seed depot. Red circles indicate examples of consumed seeds.

Consistent with the hypothesized consequences of wolf occupancy, predation of seeds of three tree species was more than 25% lower inside wolf territories areas across two years. Rodent abundance was more than 40% lower in high-wolf areas during one of two study years: a result primarily driven by low southern red-backed vole (Myodes gapperi) abundance in wolf territories. The absence of significant habitat differences between high- and low-wolf areas that might affect rodent abundance or activity further supported these results. Together, our findings suggest that top-down effects of wolves on seed consumption by rodents and seed survival may occur inside wolf territories.

Accounting for the effects of interactions among carnivores on lower levels on the food chain may allow for more accurate predictions of large-scale patterns in seed survival and forest composition, as well as other important ecological processes. With the knowledge of the activity of relatively few individuals of an apex species (e.g., wolves), we were able to predict considerable variation in rodent abundance and seed survival. This finding has important practical applications in forest management; since the majority of U.S. forests rely upon natural regeneration of harvested forest stands (i.e., recruitment from seeds, as opposed to planting), understanding how top predators influence seed survival may allow forest managers to predict which stands are more likely to experience recruitment failure after harvest. Territory boundaries of apex predators may also predict patterns of ecological interactions that influence disease prevalence. For example, small mammals are important intermediate hosts of the bacteria that causes Lyme disease in humans. Areas between predator territories may be areas of high rodent abundance, and therefore, may indicate locations of increased Lyme disease risk to humans. Consideration of the top-down effects of carnivore interactions may shed new light on spatial patterns in many ecological processes with economic, human-health, and conservation consequences that may have otherwise been dismissed as anomalous.

Hiding in plain sight: Why would a butterfly have a greenish-blue band?

Blog written by Eunice J. Tan, Bodo D. Wilts and Antónia Monteiro. Read the full article here.

Animals have a bewildering variety of colour patterns, many of which provide protection from potential predators. However, to identify how these colour patterns, or “signals”, serve to protect the animals can be often challenging.  

Research in the last decades have focused on the mechanistic origin of colour in animals (e.g.Srinivasarao (1999)) and on understanding how various signals function to protect animals (e.g. Stevens and Merilaita (2009)). An important strategy, crypsis, prevents the initial detection of the animal. There are two main ways how animals become cryptic: one way is to have colours that allow them to blend in with their background, thus making the animal’s shape difficult to detect or recognise; another way is to have continuous patterns, such as bands, traverse different but adjacent body parts, thus making it difficult to detect or recognise individual body parts.

Butterflies are well-known for their dazzling colour patterns, but the functions of these patterns are still poorly understood. The Banded Swallowtail butterfly, Papilio demolion demolion, is a mostly black butterfly with a greenish-blue band that crosses the wings (Image of butterfly below), but the origin and the function of the greenish-blue band was unknown. These butterflies occur across Southeast Asia to Australia, can be found in forests and forest edges, and are active and fast fliers, feeding on flowers of shrubs and trees.

Habitat photograph of the Banded Swallowtail butterfly, Papilio demolion. Image credit: Sin Khoon Khew.

To better understand how the colour pattern of the Banded Swallowtail protects the butterfly, we examined the butterfly wing scales that make up this pattern closely with a scanning electron microscope. This allowed us to compare the colours of the green-blue band with the surrounding black wing. We found that this blue-green colour is caused by pigments immersed in the scales, resulting in a matt appearance. Potential predators therefore see an identical green-blue colour pattern from any observation angle.

We hypothesized that the greenish-blue band of the Banded Swallowtail protects it from predators through two possible means: i) its shape could help disguise the butterfly outline, and ii) its greenish-blue colour could help blend it with the surrounding green vegetation, thus preventing recognition by predators.

To test our hypotheses, we created four types of paper butterfly model, imitating the Banded Swallowtail butterfly at rest. The first paper model was like that of the natural butterfly (Model A). In order to test the protective function of the green-blue colour, we created a greyscale version (Model B). Next, to test the protective function of the shape of the band, we distorted the band so that the band is discontinuous (Model C). Finally, to test the protective functions of both the band shape and its green-blue colour simultaneously, we created a greyscale version with a distorted band (Model D). We placed these paper models, with mealworms attached as live baits, in the natural habitats of the Banded Swallowtail, in Singapore. To monitor the predation on the paper models, we checked the models daily over three days, to see if the mealworms had been eaten.

Paper models of the Banded Swallowtail. Image credit: Brent Tan

We found that the natural-looking models (Model A) suffered the least predation, while the grey model with distorted band (Model D) suffered the highest predation. Both models that had only the colour or shape of the band changed (Models B and C) suffered similar, moderate predation.

Our results indicate that both the colour and the shape of the band are important to protect the butterfly. We suggest that the shape of the band helps disguise the butterfly outline, and its greenish-blue colour, by matching the surrounding green vegetation, helps further in preventing recognition by predators.

The presence of bands on animals is an intriguing feature. Bands were shown to reduce predation in other invertebrates such as in another species of butterfly, and in spiders (Hoese, Law, Rao, & Herberstein, 2006; Seymoure & Aiello, 2015). In fish, bands are more frequently found on the bodies of fast-moving fish (Barlow, 1972). We speculate that bands are effective in disguising fast-moving species across a range of animal species, including the fast-flying Banded Swallowtail.

We also considered whether the green-blue colour could be a warning colour, i.e., a colour that warns predators about a prey’s unpalatability. The Banded Swallowtail is probably palatable because the Banded Swallowtail larvae feed on the leaves of non-toxic plants. However, not all warning colours signal unpalatability, some of these colours could be used to signal unprofitability. Pinheiro, Freitas, Campos, DeVries, and Penz (2016) showed that warning colouration in butterflies can also function as a signal to indicate difficulty of capture by insectivorous birds. As the Banded Swallowtail is a strong flier, its blue-green band may serve as a warning colour to signal unprofitability to potential predators.

Both the colour and the band of the Banded Swallowtail may help it form a mimicry ring with other similar-looking local species. Animals in a mimicry ring look similar and advertise their common unprofitability to predators. In fact, the Common Bluebottle butterfly, Graphium sarpedon luctatius, may be involved in a mimicry ring with the Banded Swallowtail. We have seen both butterfly species in the same forests, and both species possess green-blue bands across black wings.

While our experiments cannot distinguish whether the natural-looking models were least attacked because of crypsis or warning colouration, future experiments could test this. Following previous studies (e.g. Wüster et al. (2004)), the predation rates of models in a background with vegetation versus in an artificial grey background could help distinguish among these two possibilities.

Does community-based wildlife conservation work?

Blog written by Talia Speaker, Seth Thomas and Christian Kiffner. Read the full article here.

Since the turn of the century, community-based natural resource management models have risen to the forefront of conservation efforts around the globe. And for good reason—they gained popularity for their promise of meeting both livelihood and conservation goals through empowering local communities to sustainably manage their own land and resources. Particularly in ecologically rich, yet economically poor regions (including many regions in sub-Saharan Africa), this conservation approach sounds like a win-win solution for both human communities lacking basic commodities and declining wildlife populations. But how effective are these conservation models in practice?

Research on these questions has raised major concerns about the socio-economic consequences of current community-based conservation models; namely the results of poor governance and unequal benefit-sharing. These concerns are valid and require urgent attention, but another equally important question has been lacking in the literature: Are these community-managed areas meeting their conservation goals? A handful of studies across East Africa over the last decade suggest a tentative ‘yes’ to this question, but few of these areas have long-term wildlife monitoring programs in place that can be used to assess their sustainability.

Elephant and wildebeest use the swamps and grasslands of Tarangire National Park during the dry season.

Our research takes an important step in addressing this gap by investigating how wildlife populations in a community-based Wildlife Management Area in Tanzania compared to a neighboring state-managed national park over an eight-year study period. More specifically, we tracked changes in species richness and population densities of ten mammal species in both locations from 2011 to 2018 using seasonal and time-matched walking and vehicle based transect surveys. By comparing the community-based model to a national park, we tested it against the “gold standard” of species conservation models, which prioritizes conservation and removes most human disturbances.

Zebra and wildebeest herds aggregate along the Tarangire river during the dry season.

Our results are largely promising. We found that both species richness and population densities across species were comparable between the park and community-managed area, suggesting that these areas can support wildlife communities that are similar to those of a national park, despite different management schemes. We also noted significant increases in the populations of at least three species (elephant, wildebeest, and impala) in the Wildlife Management Area throughout the study period, which further supports the conservation effectiveness of the model but raises concerns about potential negative effects (e.g. crop raiding) of growing wildlife populations on local livelihoods.

Zebras drinking from the Tarangire river during the dry season.

While these findings are good news for this specific Wildlife Management Area, our work is far from done. On a local level, persistent conservation efforts and adaptive management will be critical to the continued success of the wildlife management area model. In the bigger picture, this research only sets the precedent for a much-needed widespread effort to monitor and evaluate the long-term conservation value of community-based models across Tanzania.

Zebras standing in the grasslands of Burunge Wildlife Management Area.

For too long it has been assumed that effective management will come as a de facto result of the (partial) ownership and direct economic benefits derived from wildlife. In our study area, this assumption appears to be valid. We advocate for similar, rigorous assessments of the ecological effectiveness of community-based conservation schemes to test their effectiveness and inform adaptive management. Ideally, assessments are done neither from a wildlife-only nor a livelihood-only perspective but from a holistic and interdisciplinary perspective that takes the social and ecological components into account. To capitalize on this model that holds real potential for facilitating the coexistence of people and wildlife, we must invest now in monitoring its effectiveness and sustainability.

Widespread, generalist birds are riding the wave of Amazon deforestation

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

Experimental clearcutting (north of Manaus, Brazil) leaves behind habitat that is very unlike the surrounding rainforest. Photo by Angélica Hernández Palma. 

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.

One idea is that species might colonize recently cleared areas by traveling along roads, which offer corridors of habitat for species that cannot use mature forest. This is BR-174, the major highway that slices through the rainforest for 1000 km north of Manaus. Photo by Cameron L. Rutt.

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?

Yellow-headed Caracara (Milvago chimachima) is part of the vanguard of species that arrived after the creation of three cattle pastures. Photo by Cameron L. Rutt.

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.

The Variable Chachalaca (Ortalis motmot)—a species that favors dense vegetation following disturbance—has now made inroads into expansive tracts of rainforest. Photo by Anselmo d’Affonseca

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.

The Shiny Cowbird (Molothrus bonariensis) is one of about three-dozen widespread habitat generalists that quickly colonized the cattle ranches after clearing. Photo by Cameron L. Rutt.

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.

A number of established colonists, such as this striking Chestnut-bellied Seedeater (Sporophila castaneiventris), have declined as the forest recovers. Photo by Anselmo d’Affonseca.

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.

However, birds like this female Black-throated Antshrike (Frederickena viridis) rely exclusively on intact, pristine rainforest and do not occur in regenerating forests, even after >30 years. Photo by Cameron L. Rutt

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).

The shortest way from Belgium to Congo leads through Prague

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.

Fieldwork surrounded by elephant grass in Garamba National Park. Photo copyright – African Parks.

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.

Kordofan giraffe standing up after immobilisation, fitted with a harness satellite collar. Photo copyright – African Parks.

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?

Kordofan giraffe in Garamba Nationa Park. Photo copyright – African Parks.

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.

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