Songs of the Forest: deciphering changes in species richness from the forest edge

Ben and Kathleen with a camera trap in a clearing where they spotted an ocelot
Ben and Kathleen with a camera trap in a clearing where they spotted an ocelot

As the quarter comes to a close, we reflect on the work that has gone into our research projects during this eye-opening field biology quarter. We have had an irreplaceable time in the field, and brought home some interesting observations from both our studies! Our conservation project tried to determine how the number of bird and mammal species change as the distance from the forest edge increases. We focused on mammals and birds as they are easy to detect and identify. Additionally, we attempted to identify frugivorous birds, or fruit eaters, and characterize their richness in relation to the forest edge-interior gradient. Frugivores are key species as both animals and trees depend on their role in the rainforest ecosystem as vital seed dispersers.

For our survey, we chose three zones of different distances from the edge of the forest as study sites. These three zones represented the edge, intermediate, and interior forest habitats. Every morning and evening, we recorded birdcalls at each point and set up motion sensor cameras to record mammals. At each point, we also recorded various qualities of the habitat, such as temperature, humidity and wind speeds. It was definitely an enjoyable process collecting data!

In total, we catalogued 117 different birds, identified 18 frugivorous bird species, and even spotted an ocelot! Overall, we didn’t find any solid differences when we compared the total number of species found in the three zones. The intermediate zone always had the highest number of birds and mammals out of the three, but not by much. This may be due to the presence of fresh logging sites near the edge and interior zone that caused a change in the forest dynamics. Therefore, the intermediate zone was most similar to primary undisturbed rainforest in terms of habitat characteristics, having the highest percentage of canopy cover and little human disturbances.

When we broke the data down to the time of day however, we found that there were differences in the number of species found in the mornings as compared to the evenings. These differences were only found in the intermediate and interior zones – which may point to the presence of more specialist species compared to the edge zone – even though all three zones had roughly the same number of species. This was supported by the fact that the interior zone had the highest number of frugivorous species of the three.

With the recent ground breaking of the Nicaraguan transcontinental canal it is vital the developers take into account how human disturbance and infrastructure will influence forest dynamics. The frugivorous birds will definitely be affected by the fragmentation of the forest. To maintain the diversity of species present in the rainforest, developers must acknowledge the importance of a buffer zone between the canal and even proximate regions of the forest.

The Effects of Tourism on a Poison Dart Frog

strawberry poison dart frog
strawberry poison dart frog

For the past 11 weeks we have been participating in a Field Biology Quarter for UCLA. We have planned two projects, travelled to a private section of rainforest in Nicaragua, hiked and collected data daily for three weeks, and came back to UCLA to analyze the data and sum up our projects in two papers. We have learned an immense amount, mostly on how challenging the complete process of carrying out a research study from start to finish can be. We are here now to tell you a little bit about one of our projects, in which we spent hours on end listening for the calls of strawberry poison dart frogs.

Ecotourism is growing in popularity and bringing with it anthropogenic effects to areas previously not exposed to human noises. These noises come from motorboats passing by edges of rainforests, airplanes flying by, and hikers hiking through trails of rainforests. We were interested in studying the species Oophaga pumilio, otherwise known as the strawberry poison dart frog. This frog is very recognizable with its red body and blue legs, while the males also have a very distinguishable call. The males of this species call to advertise their territories and to attract females to mate. We looked into multiple aspects of human interference with the calls in this species.

We conducted two experiments during our time in Nicaragua. In the first, we hypothesized that larger groups of hikers will have more of an effect on the call characteristics of a frog in comparison to small groups. In the second, we hypothesized that frogs residing near to a human settlement will respond differently to hikers passing by than frogs residing farther from human presence.

We found that hiker group size and distance to human settlement did not have a main effect on different aspects of frog calls. This is positive news for the frogs, as the presence of humans walking and talking along trails does not seem to have negative impacts. An aspect that we were not able to study with the calls of the strawberry frogs is the fundamental frequency of call, which has been shown to change in response to urban noise in other species.

Lindsey recording a calling frog
Lindsey recording a calling frog
Jeff listening for frog calls
Jeff listening for frog calls

Foraging habitat preferences and predator avoidance in the Central American Agouti

An agouti in the open (photo by K. Yap)
An agouti in the open (photo by K. Yap)

For our conservation project, we focused on the foraging behavior of the agouti in Refugio Bartola, Nicaragua. We were interested in the potential effects of selective logging on agouti fitness, which may have important conservation implications due to their importance as an important seed disperser and as a food source for many large predators. It is known that selective logging can reduce understory cover, which is known to serve as protection from predators for some species of small mammals.

From previous studies, we knew that agouti restrict their activity to times when predator activity (primarily ocelot and other large cats) is lowest. This is an important general concept in animal behavior – all organisms must acquire resources to survive, but foraging exposes them to increased levels of predation, and thus they must evolve behaviors that resolve this tradeoff. We were curious if agouti might also utilize spatial mechanisms of predator avoidance to do this, selectively foraging in areas in which they are better hidden from predators, and whether this preference varies during the day as predator pressure varies. From a conservation standpoint, this is important because decreases in understory cover from logging may have significant and complex effects on agouti fitness if this is indeed the case; given their important roles as prey and dispersers, this could have cascading effects on the structure and functioning of rainforest communities.

In order to test whether populations of agouti and other small mammals in the Nicaraguan rainforest exhibit such a preference, we studied their foraging habitat selection through a camera trap study. We baited sites of both dense understory cover and open understory cover, with at least one of each near previous agouti sightings, but with a minimum distance exceeding that of the agouti home range size, in order to minimize resampling the same individuals. The sites were restocked with bait every other day, and we observed them for between 4-12 days. We then were able to convert the images into foraging rates (visits per unit time) for different periods of the day in open and closed understory, which allowed us to examine the interaction of time of day (as a proxy for predator pressure) with preference for these different degrees of cover.

Our study yielded interesting but counterintuitive results – interestingly, the primary interaction of foraging rate with time of day was in closed understory. In dense understory, at times when predation is highest (just following dusk according to the literature) agouti foraged at much lower rates than at times when predation is thought to be lower (dawn and day). However, in open understory, there was much less of a difference between dusk and daytime foraging rates, and no difference between dawn and dusk foraging rates. This is the exact opposite of what we predicted: we would have expected that there would be a larger response to predation pressure in open understory, where the agouti are more exposed. However, this may make sense – agouti are known to cache food in open areas, and their main – and successful – means of escape from predators is to observe them before they attack and run away. Thus, open understory might actually be more protective from predators than closed understory – while agouti can be seen more easily, they can also see predators more easily. To get at this question more deeply in the future, studies would need to quantify the actual levels of predator pressure at different times in different areas of cover, which we were unable to do due to time constraints.

Effects of Ecotourism on Leafcutter Ants

Tinh and Emily in the field
Tinh and Emily in the field

The leaf cutter ants are a quintessential component of the rain forest. They deliver an iconic image of the rainforest through their magnificent trails, but beyond this their ecosystem services truly keep the rainforest thriving. As ecotourism rises, the effects of increased human foot-traffic and disturbances pose a real threat to the pristine rainforest we strive to go see. These disturbances can be felt at an immediate level, even caused by our very own footsteps. The leaf cutter ants pave trails all throughout the rainforest, and these trails commonly intersect with manmade trails. When the ants are not using the trails to forage, they can be seen in the colony taking care of broods or tending to their fungal garden for food. Disturbances on their trails force these worker ants to divert their energy from colony maintenance in order to maintain the trail.

As ecotourism promises to merge our world with theirs, we asked how human disturbances affect the activity in leaf-cutter ant trails. We ran a two-part study to look further into this. Experiment 1 consisted of studying how different hiker group sizes affect ant rates. We hypothesized that as we increase the group size disturbance and damage to the trail, this would ultimately lead to a decrease in activity rates of leaf cutter ant trails. For Experiment 2, we were interested to see how the frequency of visitations affects ant rates. We hypothesized that as the frequency of the disturbance increases from 1 to 3 to 6 times, the activity rates of the ant trails would decrease according to the treatment.

For Experiment 1, we found that overall there was a significant effect of time but not of treatment. What this means is that after the disturbance treatment, the activity rates of the trails were significantly different than from the control trails that did not receive any disturbance treatment. For Experiment 2, we found that overall only time had a significant effect. This means that although the specific treatments didn’t have an effect as time progressed, overall activity rates were significantly different after the disturbance. From both of these experiments, we found that group size and frequency of visitation didn’t have a significant effect. However, our results show how disturbances as a whole do have an effect on the activity rates of leaf cutter ant trails over time. Also, at the beginning of the study, we predicted that the smallest disturbances would not significantly impact the ant trails. However, our results show that even the smallest disturbance did affect activity levels. Although more research still has to be done, we have found that human activity weighs in on leaf cutter ant activity, and that ecotourism should be approached carefully in order to preserve these wonders of the rainforest that continue to fascinate us.

Beautiful Bromeliads


A tree by the Rio Bartola is filled with tank bromeliads
A tree by the Rio Bartola is filled with tank bromeliads

Bromeliads belong to a family of plants native to the Neotropics. Some species of bromeliad are epiphytes, meaning that they grow on other plants similar to lichen or moss.  Several species of bromeliad have a center rosette that can trap pools of water—known as a phytotelma. These species are commonly referred to as tank bromeliads.    As one would expect in streams or other bodies of water, bromeliad phytotelma are a valuable resource for many animals, especially aquatic and semi-aquatic macroinvertebrates, which often rely on perennial water bodies to reach maturity or even remain in aqueous environments for their entire lives.

Bromeliads remain understudied and even less is known about the communities they host.  While it has been shown that the type of forest cover above a stream can have an impact on the invertebrates that live in them, this principle has not been thoroughly addressed for bromeliads.  We were interested in how the amount of canopy closure above a bromeliad could affect the diversity and abundance of invertebrates within their phytotelma.  We looked at bromeliads between areas of closed canopy cover and areas in the open, where light could more easily permeate the canopy tops.  We predicted that bromeliads on trees in open areas would have significantly less invertebrates within their phytotelma than bromeliads from within the forest due to the likely linkage between canopy cover and water permanence.  We assumed that with less water due to a difference in cover, these phytotelmata communities would be more vulnerable to desiccation (a process by which animals dry up and perish).

Joey and Michelle pipette water (and inverts!) out of a bromeliad
Joey and Michelle pipette water (and inverts!) out of a bromeliad

Pictured above, we collected data from the bromeliads by removing the liquid and soil contained in the phytotelma and sorting invertebrates found within. We collected a total of 299 invertebrates from 20 bromeliads, half from closed canopy cover and the other half from open areas.  As we predicted, bromeliads under more canopy cover contained more water, soil, and most importantly, had greater abundance and diversity in their invertebrate communities.

The future of Nicaraguan tropical rainforest is marked with discontent due to the increased prevalence of selective logging, a process where the largest trees within a forest stand are removed for their timber as an alternative to clear-cut logging.  It has been shown that the removal of trees within a forest leads to changes in local humidity and temperature that can result in a reduction in the presence and diversity of bromeliads.  Similarly, by removing trees from a forest, area on which bromeliads can grow is lessened.  Our study shows that not only does selective logging have an effect on bromeliad communities within tropical forests, but also on the communities that reside within them.  It is apparent that in order to protect these centers of biodiversity, we must seriously consider the impacts of global forestry practices.

We’d like to thank our professors and TAs for their advice and assistance in the field. We would also like to thank the staff at Refugio Bartola for all of their hard work, our fellow FBQers for positivity, and our friends and family at home for their continued support. Finally, we’d like to thank the bromeliads and macroinvertebrates that were integral to our study.

(Water) striding towards the finish line

Callan and Vivien measuring fish by a stream impacted by the tourist lodge
Callan and Vivien measuring fish by a stream impacted by the tourist lodge

According to the World Health Organization, 4% of global diseases are caused by contaminated water. At Refugio Bartola, Nicaragua, humans frequently interact with water sources, both as a washing or drainage system. Therefore, we took special interest in how water quality affects species richness and abundance in the rainforest streams. We compared pools located upstream and downstream from a lodge generator and a kitchen waste pipe. We tested the water quality by examining coli bacteria presence, amount of dissolved oxygen, and creating a visual assessment of impact score (presence of bubbles, foam, oil, and murkiness) for each examined pool. Our hypothesis is that anthropogenic impacts will affect species richness and species abundance in rainforest streams, due to differences in water quality. We predict an overall decrease in species richness and abundance in pools affected by anthropogenic disturbances. Furthermore, we predict the water quality will decrease in sites affected by anthropogenic disturbances.

We found that there was no difference in species richness, species abundance, total number of fish, total number of dragonflies, and coli bacteria presence between pools above and below anthropogenic disturbances. The highest amount of coli bacteria was present in the pool downstream from the kitchen waste pipe where large quantities of food waste were transported. The pH and dissolved oxygen content was the same in all pools we tested. We did find a difference in the amount of water striders and the visual assessment of impact in pools above and below anthropogenic disturbances. A larger water strider abundance and less visual disturbance existed in undisturbed pools. Therefore, as the visual assessment of impact increased, the amount of water striders decreased.

Even though we did not seem to find a significant difference in species richness and abundance between disturbed and undisturbed pools, we did find that water striders were affected by the present anthropogenic disturbances. Since water striders were affected by the presence of a generator and food residue from a kitchen waste pipe, it is not difficult to imagine what would happen to this species or any other aquatic species if they were exposed to more serious forms of pollution, such as an oil spill or toxic waste. In addition, large groups of tourists only come to this ecotourism lodge every couple of months, or in our case, every two years. If the disturbance levels increase, then species richness and abundance will most likely decrease. However, we might not have reached the threshold of disturbance yet to detect a distinct difference between impacted and non-impacted pools. Moreover, our experiment provides a good baseline for future projects that could examine the effects of large-scale anthropogenic disturbances on animal species.

The Impervious Ant

The Neotropics are at the forefront of all future extinctions. As an alternative to clear-cut logging, which has destroyed approximately 40 million hectares over the past 10 years, selective logging aims to improve how we remove natural resources without severely damaging the environment. Some species thrive in selectively logged areas, while other severely decline in abundance. Therefore, we must look to indicator species, like ants, to best understand the impact we impose on the environment.

An ant carries a cut leaf back to the burrow to add to the fungal garden
An ant carries a cut leaf back to the burrow to add to the fungal garden

The focal species for our study, the leaf-cutter ant (Atta cephalotes), use their mandibles to cut off small pieces of leaf that they use to create fungus gardens underground that they consume. Leaf-cutter ants are the best indicator species because they are the primary herbivores in the forest, as they respond quickly to environmental changes and can indicate the welfare of other species because of their pivotal role in the forest ecosystem. Studies of leaf-cutter ants in secondary forests surprisingly suggest that they do 30 times better in selectively logged tracts of forest despite the increased fluctuations of temperature, humidity, and direct sunlight on the soil. Therefore, we wanted to see if the expected habitat preferences of leaf-cutter ants differ between primary (undisturbed) and secondary forest sites in a Nicaraguan rainforest. We hypothesized that those habitat characteristics that are essential to the survival of the leaf-cutter ant colony, like stable air temperatures, would differ between primary and secondary forests. We predicted that, in secondary forests, there would be greater fluctuations in air temperature, humidity, soil temperature, and soil moisture.

Ultimately, we found that although secondary forest sites had a greater percent of open canopy above the colonies, the ambient air temperature and humidity did not differ between sites. We think this might be because leaf-cutter ants can alter their surroundings by churning up the soil when digging new tunnels and cutting down the leaves of only specific plant species. We also found that the primary forests had higher levels of activity than that of the colonies in secondary forest. A possible explanation for this might be because plants in primary forests have more chemical defenses than plants found in secondary forests; therefore, ants need to travel further in primary forests to find edible plants. Finally, we observed a behavior in which workers place cut leaves around the perimeter of mounds within the colony and we found that this behavior happens more frequently in secondary forest sites. Since secondary forest sites had higher soil temperatures, but soil moisture did not differ between sites, we think that the placement of these cut leaves acts as a thermal blanket. The leaves might keep the chambers underground humid so that fungal gardens are able to grow despite being in a secondary forest.

In light of conservation, studying how an indicator species that thrives in a damaged forest can give us better insight into how we are impacting the ecosystem as a whole.

Weather vs. Callan

Callan studies the behavior of a frog on her head
Callan studies the behavior of a frog on her head

Hot. Wet. Sweat.
Dripping down with each incline.
From merely breathing.
From merely moving.
From merely being still.

In retrospect, the climate never really crossed my mind before coming to Nicaragua, however big it may have influenced my daily schedule in the rainforest. Yes, I did not believe the weather would remain at a constant fixture (because it is the Neotropics); but, the impact of an ever-changing environment was not evident until data collection was crucial.

I remember waking up around 2:30 am to the heavy pitter patter of rain on the metal roof and thinking, “The rain will stop around 5:30 am; enough time for our dragonflies to readjust to their habitat.” But the rain did not stop. It did not stop for three days. What was even more frustrating was that we could not collect data for our water quality project since the usually clear water was too murky and full of soot to count animal abundance.

Eventually, the rain did stop. But my partner and I were on hyper drive, anxious to recover the bits of data we failed to collect. So we became more flexible with our schedule in order to complete more dragonfly trials.

The humidity…now that was something else entirely. You could walk for less than 2 minutes and feel as if you jumped head first into a river. Once or twice I would joke and dramatically tell Vivien to “go on without me” as I wiped the sweat from my face whenever we started hiking up a trail.

But the humidity did not affect me until stress affected me. Until I worried about making a mistake. Until I feared that I was not respected. Until I felt somewhat homesick. Until I wanted to know how my mom, dad, and brother’s day went. Until I questioned my life goals.

So I would close my eyes when I was in the rainforest and breathe in deeply. Taking in the sounds and smells, remembering that this is exactly where I want to be. Where I am destined to be. Working. Right. Here.

There will be high stress events involved in science. It is just how you adapt to those situations that either make or break you. I believe Vivien and I were capable of handling ourselves well when the weather was not optimal. I even believe Vivien and I were very compatible partners, so I am grateful for that. This experience will definitely be one I will not forget. It will always be the first of many: research projects, rare animal sightings (!!!), and true independent range on what scientifically interested me.

On the last day, my friend Brigit and I walked the length of the Rio Gaitan. This was perhaps my most favorite memory. I have never seen such untouched beauty and peace. It looked like a dream. And when I felt the humidity and the sweat, I welcomed it with open arms for I was saying goodbye to an old friend.

Back to Reality

Emily's gopro group shot
Emily’s gopro group shot

Being back home has definitely made me reflect about my time in Nicaragua. I feel that we were so busy while we were there that there was really no time to just sit down and take a breather. I think my one outlet of letting everything spill about how I was feeling or what happened that day was writing in my journal every night. I have been reading some of the entries I wrote while I was there and it felt like I was going way back in time years ago when it was really just about a week ago.  Also, I’m so happy that I was able to bring a GoPro to Nicaragua (quick shout out to Victoria for being the kindest best friend and letting me borrow it!). Last night, I finally downloaded all the videos and pictures and I was having so much fun being able to replay some of those memories. It was also very heartwarming to see how much we evolved as a group. In the first video you see how everyone is still getting comfortable with each other, politely waving at the camera. On the last video, people are jumping across the camera, making the silliest of faces, singing, laughing, hugging, and taking pictures with one another. I’m glad I was able to meet such a great group of people.

I think the biggest thing about being back has been seeing how it’s the little things that matter. For example, for the whole time we were there it was always cold showers. The first hot shower I took at home honestly felt like heaven. Being able to use conditioner and actually be able to brush my hair was amazing. Having a laundry machine that thoroughly washes your clothes is such a privilege. I’m so happy that I am now able to value these things more. I think trips like these are important because sometimes we get so caught up living in such a fast-paced society that we forget to cherish the little things.

In whole, this trip was far from what I expected it to be. When they say you do field work every day, they literally mean every day. What are weekends? When they say you really get to know the 15 other students, they are not lying. When they say you will get frustrated with your project, it’s definitely true. And when they say this experience will be one of the highlights of your undergrad career, there couldn’t be a truer statement.

Memories of the Rain Forest


Jeff holding a Cloudy Slugeater snake
Jeff holding a Cloudy Slugeater snake

A week has passed since arriving back in Los Angeles, and my time in the rainforest is nothing more than a memory (one that is constantly reinforced by the analysis of the data we have collected). Since the time I have been back, I have recited my elevator pitch to almost everyone I have spoken to, including during an interview for a graduate school program. I am consistently asked how my time in Nicaragua was, and the most appropriate answer I can think of is “amazing”.

I had so many expectations going into the trip. It was my first time outside of the United States, so I was expecting to be essentially placed into a whole new world. In some cases it did feel like I was in an entirely unfamiliar place, especially during the night hike we took during our first night in Refugio Bartola. It was honestly a little overwhelming in the beginning, but as time progressed, I soon became adjusted to my surroundings. My childhood dream of traveling to the rainforest, something I had long given up on, was realized.

Like I mentioned in my previous blog post, one of the things I did not anticipate fully was the amount of hard work we would be doing. I was so used to the classroom setting that I did not consider that hiking miles through the rainforest is also a very valid teaching tool. That’s not to say that I did not expect to be working hard at all. I was fully prepared for what was thrown at me.

What made this trip so amazing is that I was able to devote my entire being to the experience. Without the distraction of cell phones and computers, there was no excuse not to take an opportunity to see something cool, such as a sloth or a cool insect that was brought back into camp. I knew that I would see a large variety of wildlife, but knowing you would see something and actually seeing it are two very different things. Looking back at my photos, I realize that nothing will ever be as good as actually being there. The excitement of seeing an animal in its natural habitat is something that will always stick with me.

In the future, if I am given the opportunity to travel to a rainforest setting (or anywhere else, to be honest), I would gladly say yes. This first traveling experience showed me that I really do love nature and that I want to experience more of it.