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Standing in the forests at the foothills of mountains across Asia, Australia, and parts of Africa, hungry insect-eating birds seem to cry out: “Where have all the insects gone?” To their surprise, the weaver ants have devoured them all. These reddish, giant ants swarm the forest floor, feasting voraciously on insects—a familiar scene often portrayed in nature documentaries. Weaver ants consume so many insects that they leave little to nothing behind for the birds.

A team of scientists, led by Umesh Srinivasan from the Centre for Ecological Sciences at the Indian Institute of Science, found that in the foothills of mountain ranges across the world where weaver ants reside, the number of insect-eating birds is low. “Oecophylla [weaver ants] and insectivorous birds have highly overlapping diets,” said Srinivasan, Assistant Professor at CES. “As a result, where Oecophylla ants are present at the base of mountain ranges, the species richness of insectivorous birds is low, while the species richness of all other birds is high.”

Srinivasan, who researches climate change and bird interactions in the eastern Himalayas of India, was ignited to explore the relationship between weaver ants and insect-eating birds after a colleague in Darjeeling, India, prevented these ants from infesting trees. It was found that trees without weaver ants had more insects than those with ant infestations. Srinivasan said he had been curious ever since learning about the experiment, especially since weaver ants are considered the “oldest biological control agent.” He noted that Chinese farmers have long used weaver ants in their orchards to control insects and pests. “So they’re very effective insect predators,” added Srinivasan.

So, Srinivasan’s team categorized birds into three groups: insect-eating, omnivorous (which eat both insects and fruits), and fruit- and nectar-feeding. They then analyzed global datasets on bird elevation and recorded the lower and higher elevations at which birds lived in the observed mountain ranges. Afterward, they counted the number of bird species at different elevations in each mountain range and correlated it with the presence of weaver ants.

The research team found that where weaver ants are present, the number of insect-eating birds was lowest at lower elevations, with the bird population stabilizing only after reaching an altitude where the ants no longer exist. The population of these birds peaked at mid-elevations, around 900 meters, which is “over 400 meters higher than in mountains without Oecophylla,” the researchers wrote in their paper published in August in Ecology Letters. They also observed a “similar but weaker” pattern for omnivorous birds, with their population peaking around 700 meters higher, indicating that omnivores are less affected than insect-eating species. For other bird species, Srinivasan noted, “species richness is highest at low elevations,” suggesting that fruit-eating birds are not significantly impacted by the presence of weaver ants, as their population peaks at lower altitudes and steadily declines with increasing elevation.

“Birds eat a lot of things. Some species eat only insects, some eat only fruits, others are omnivores, and some are scavengers like vultures,” Srinivasan explained. Since weaver ants fiercely compete with insectivorous birds for the same food, only a few insect-eating birds thrive in areas where the ants are present: “Less food, less birds.” 

For hundreds of years, people have proposed numerous ideas to explain the causes behind the uneven distribution of species across elevation gradients: “Temperature, rainfall, area, and various other environmental factors,” Srinivasan said. Another factor is competition between species for resources, which Srinivasan noted hasn’t received much attention—especially competition between species that are distantly related to each other. In fact, the researchers also analyzed factors like precipitation and productivity, but they found these had less impact on the birds compared to the influence of the ants!

This new research—which exposes the link between weaver ants and insectivorous birds—is significant because it presents a new perspective on the question of why species numbers vary in different parts of the world, which is a “fundamental scientific curiosity,” added Srinivasan. Furthermore, he emphasized the rapidly changing global climate that is pushing species higher up the elevation gradient. “Because of rising temperatures, species are shifting their ranges to higher elevations,” he added. “This is not migration; this is actually a permanent shift in the range of species to higher elevations,” Srinivasan clarified. “So if these ants shift their ranges upwards, what will happen to the bird communities?”

Ben Freeman, a biologist at the Georgia Institute of Technology who was not involved in the study, told Science Magazine that he considers this new hypothesis “a big-time idea, that it’s ants that shape insect-eating bird communities.” Although Freeman finds the idea interesting, he expressed a desire to see it tested experimentally in the future.

“This is a pattern that is consistent with one hypothesis,” Srinivasan added. “It's difficult to get proof of a hypothesis like this when what you’re actually asking questions about are at the global scale.” He stated that since it is extremely challenging to prove this hypothesis through large-scale experimental studies, “We can only say that this might be one of the reasons why we see a difference in species richness patterns across a global scale.”

Recent research has brought attention to a concerning trend in waste studies in Nepal: a strong emphasis on urban areas while rural regions are often overlooked. The researchers note that traditionally, rural communities managed waste according to local customs and economic factors. However, with changing lifestyles and an uptick in tourism, waste management in rural areas has become increasingly complex. The research also warns that ineffective waste management practices in rural settings could worsen environmental problems.

Every year, Nepal now welcomes over a million tourists, establishing itself as a thriving destination for travelers worldwide. Tourism benefits Nepal by driving economic growth, creating jobs, promoting cultural exchange, and supporting the preservation of its rich heritage. Conversely, tourism in Nepal also presents challenges such as increased solid waste generation, as evidenced by studies conducted in countries like China, India, and Ukraine.

Now it’s not just the Nepalese cities facing solid waste management challenges anymore; rural areas are grappling with them too, especially in regions that are densely populated and popular tourist destinations. Recent studies by Adhikari and colleagues have shown a worrying increase in waste generation per person, especially in places where connectivity is improving, living standards are rising, and people’s consumption habits are changing. The lack of proper waste management facilities only adds to the problem, along with issues like local governments not fully committing to tackling the issue and inefficient decision-making processes. So, there’s a clear need for a detailed investigation into solid waste management problems in rural areas to find effective solutions.

Ghandruk, lying within the Annapurna Rural Municipality, stands as a beacon for tourists due to its breathtaking Himalayan vistas, diverse cultural heritage, and renowned hiking trails, notably along the path to Annapurna Base Camp. Department of Immigration data reveals that out of 83,568 foreign trekkers in Nepal in 2015, a staggering 78,926 chose to explore the Annapurna Conservation Area, highlighting the economic importance of tourism to Ghandruk.

While tourism has undoubtedly brought economic benefits to Ghandruk, contributing significantly to its social, economic, and environmental landscape, there are notable drawbacks, particularly concerning solid waste management. Mass tourism has aggravated the fragility of the mountain environment, leading to instances of environmental degradation, including the accumulation of solid waste. This issue is particularly pressing in rural tourist areas like Ghandruk, where inadequate waste management infrastructure and practices pose significant challenges to environmental sustainability and eco-tourism.

The recent research, titled “Solid Waste Management in Rural Touristic Areas in the Himalayas—A Case Study of Ghandruk, Nepal,” published in Habitat International in Jan 2024, aimed to highlight the gap in waste management studies. It conducted the first-ever waste characterization and analysis of existing solid waste management (SWM) practices in the rural tourist village of Ghandruk, situated in western Nepal. The research studied 64 households and 15 commercial sectors (hotels and restaurants). Waste from each household and commercial sector was examined over two days to quantify waste generation, with methodologies adapted from previous studies. Semi-structured questionnaire surveys, key informant interviews (KIIs), and focus group discussions (FGDs) were utilized to gather qualitative data on household characteristics, waste management practices, awareness of waste management issues, and satisfaction levels. Geographic information system (GIS) software was used for mapping, while descriptive statistics and statistical software were employed for data analysis.

What did the researchers find?

Households in Ghandruk produce 21.3 grams of solid waste per capita per day, while commercial sectors generate 240 g per capita per day. The composition of solid waste in both households and commercial sectors was analyzed, with organic waste found to be the most dominant component. Waste management practices in Ghandruk were examined, revealing a combination of household segregation, collection, and disposal methods. Efforts by local authorities, including the establishment of collection centers and restrictions on plastic bottle sales, aimed to mitigate waste generation and promote recycling.

Local residents expressed varied perceptions of existing waste management practices, with younger respondents showing greater concern for environmental impacts and older participants focusing on health hazards. Collaboration between the Annapurna Conservation Area Project (ACAP) and local communities aimed to educate residents and improve waste management practices.

The findings of the study highlighted the need for a more holistic approach to waste management. While organic waste remained dominant, there was a notable increase in recyclables like glass and plastics, indicating a shift in waste characteristics not unique to Ghandruk but possibly reflective of trends in rural tourist areas worldwide.

The daily per capita waste generation of 261.3 grams revealed by the study challenges the notion that rural areas produce negligible amounts of solid waste. This highlights the critical need to address waste management concerns in these regions, especially with the burgeoning growth of tourism.

Despite commendable waste segregation efforts, the study identified challenges such as unreliable waste collection and transfer mechanisms, posing potential hurdles in the future. Moreover, concerns regarding the handling of non-recyclable waste and frequent open burning call for systematic solutions to mitigate environmental consequences.

The implications of this research extend beyond Nepal, offering valuable insights for policymakers, operators, and regulators grappling with SWM issues in rural tourist areas globally. Recommendations include the implementation of multimodal SWM plans in collaboration with local stakeholders, including households, and incentivizing community involvement through collection fees and deposit-refund systems.

In light of Nepal’s new federal government structure, the study advocates for proactive measures at the provincial and local levels to address emerging SWM challenges effectively. By prioritizing sustainable waste management practices, rural and mountainous regions can preserve their natural beauty while accommodating the needs of growing tourism industries