When Sunflowers Follow the Sun

Tropisms are widely studied biological phenomena that involve the growth of an organism in response to environmental stimuli. Phototropism is the growth and development of plants in response to light. Heliotropism, a specific form of phototropism, describes growth in response to the sun. Discussions of heliotropism frequently include sunflowers and their ability to “track the sun.” This conjures up images of a field of sunflowers in full bloom following the sun across the sky. However cool this might sound, it simply doesn’t happen. Young sunflowers, before they bloom, track the sun. At maturity and in bloom, the plants hold still.

What is happening in these plants is still pretty cool though, and a report published in an August 2016 issue of Science sheds some light on the heliotropic movements of young sunflowers. They begin the morning facing east. As the sun progresses across the sky, the plants follow, ending the evening facing west. Over night, they reorient themselves to face east again. As they reach maturity, this movement slows, and most of the flowers bloom facing east. Over a series of experiments, researchers were able to determine the cellular and genetic mechanisms involved in this spectacular instance of solar tracking.

Helianthus annuus (common sunflower) is a native of North America, sharing this distinction with dozens of other members of this recognizable genus. It is commonly cultivated for its edible seeds (and the oil produced from them) as well as for its ornamental value. It is a highly variable species and hybridizes readily. Wild populations often cross with cultivated ones, and in many instances the common sunflower is considered a pesky weed. Whether crop, wildflower, or weed, its phototropic movements are easy to detect, making it an excellent subject of study.

Researchers began by tying plants to stakes so that they couldn’t move. Other plants were grown in pots and turned to face west in the morning. The growth of these plants was significantly stunted compared to plants that were not manipulated in these ways, suggesting that solar tracking promotes growth.

The researchers wondered if a circadian system was involved in the movements, and so they took sunflowers that had been growing in pots in a field and placed them indoors beneath a fixed overhead light source. For several days, the plants continued their east to west and back again movements. Over time, the movements became less detectable. This and other experiments led the researchers to conclude that a “circadian clock guides solar tracking in sunflowers.”

Another series of experiments helped the researchers determine what was happening at a cellular level that was causing the eastern side of the stem to grow during the day and the western side to grow during the night. Gene expression and growth hormone levels differed on either side of the stem depending on what time of day it was. In an online article published by University of California Berkeley, Andy Fell summarizes the findings: “[T]here appear to be two growth mechanisms at work in the sunflower stem. The first sets a basic rate of growth for the plant, based on available light. The second, controlled by the circadian clock and influenced by the direction of light, causes the stem to grow more on one side than another, and therefore sway east to west during the day.”

The researchers observed that as the plants reach maturity, they move towards the west less and less. This results in most of the flowers opening in an eastward facing direction. This led them to ask if this behavior offers any sort of ecological advantage. Because flowers are warmer when they are facing the sun, they wondered if they might see an increase in pollinator visits during morning hours on flowers facing east versus those facing west. Indeed, they did: “pollinators visited east-facing heads fivefold more often than west-facing heads.” When west-facing flowers where warmed with a heater in the morning, they received more pollinator visits than west-facing flowers that were not artificially warmed, “albeit [still] fewer than east-facing flowers.” However, increased pollinator visits may be only part of the story, so further investigations are necessary.

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I’m writing a book about weeds, and you can help. For more information, check out my Weeds Poll.

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Introducing Invasive Species

The terms “invasive” or “invasive species” get thrown around a lot. They are frequently used to describe anything that is “misbehaving,” or acting in a way that doesn’t fit our idealized vision for how a landscape should look and function. Oftentimes a species that is introduced (by humans) or is not native to an area automatically gets labeled invasive, even if it isn’t acting aggressively or having any sort of dramatic impact on the ecosystem. It is an alien species in an alien environment; it has invaded, therefore it is invasive.

image credit: cartoon movement

image credit: cartoon movement

Determining what is actually invasive in what location and at what time is much more complex than that. We do our best to understand the natural features and functions of ecosystems, and we single out any species, whether introduced or not, that is acting to upset things. That species is considered invasive and, if the goal is to restore the natural balance, it must be controlled. To what degree a species should be controlled depends on the degree that it is upsetting things. Ultimately, it comes down to human judgement. Hopefully that judgement is based on the best available evidence, but that isn’t always the case.

But we are getting ahead of ourselves. What I mostly want to accomplish with this post is to introduce the concept of invasive species and point you to a selection of resources to learn more about them. I defined invasive species in a post I wrote back in August 2015, so I will repeat myself here:

“Invasive species” is often used inappropriately to refer to any species that is found outside of its historic native range (i.e. the area in which it evolved to its present form). More appropriate terms for such species are “introduced,” “alien,” “exotic,” “non-native,” and “non-indigenous.” The legal definition of an invasive species (according to the US government) is “an alien species that does or is likely to cause economic or environmental harm or harm to human health.” Even though this definition specifically refers to “alien species,” it is possible for native species to behave invasively.

These terms refer not just to plants but to all living organisms. The term “noxious weed,” on the other hand, is specific to plants. A noxious weed is a plant species that has been designated by a Federal, State, or county government as “injurious to public health, agriculture, recreation, wildlife, or property.” A “weed” is simply a plant that, from a human perspective, is growing in the wrong place, and any plant at any point could be determined to be a weed if a human says so.

Invasive species are easily one of the most popular ecological and environmental topics, and resources about them abound – some more credible than others. Here is a list of places to start:

That should get you started. There are, of course, numerous books on the subject, as well as a number of peer-reviewed journals dedicated to biological invasions. You should also be aware that IUCN maintains a list of the Top 100 World’s Worst Invasive Species and that there is a National Invasive Species Awareness Week, which is quickly approaching. This episode of Native Plant Podcast with Jamie Reaser (executive director of National Invasive Species Council) offers an informative discussion about invasive species, and a search for “invasive species” on You Tube brings up dozens of results including this brief, animated video:

 

I want to believe that we are doing the right thing when we make concerted efforts to remove invasive species and restore natural areas, but I’m skeptical. The reason why I have chosen to spend an indefinite amount of time exploring the topic of invasive species is because I truly want us to get it right. Yet I don’t even know that there is a “right.” It seems to me that there are endless trajectories – each one of them addressing different objectives and producing different outcomes. In a way we are playing God, regardless of which approach we take. We are making decisions for nature as if we know what’s best for it or that there even is a “best.”

Humans have had major impacts on virtually every square inch of the planet and have been placing our fingerprints on every ecosystem we touch since long before we became the humans we are today, and so it is difficult for me to envision a planet sans humans. It is also difficult for me to buy into the idea that our planet should look as though humans haven’t touched it (i.e. pristine). Because we have been touching it – for hundreds of thousands of years. Efforts to rewind time to before introductions occurred or to hold an ecosystem in stasis, securing life for only those species that “belong” there, seem noble yet fanciful at best and misguided, arrogant, and fruitless at worst.

To be the best conservationists we can be, we probably need to find a middle ground regarding invasive species – not a deter and eliminate at all costs approach, but also not a complete surrender/all are welcome and all can stay stance. Somewhere in between seems reasonable, acknowledging that the strategy taken will be different every time based on the location, the species in question, and our objectives. Of course, none of my beliefs or opinions on this topic (or any topic for that matter) are fully formed. I am trying to do my best to maintain an open mind, seeking out the best information available and following the evidence where it takes me. A topic as complex as invasion biology, however, is never going to be easy to finalize one’s opinions on, and so this journey will be boundless. I hope you will join me.

tea-bag

Last but not least, here are two articles that discuss updating our approach to dealing with invasive species:

 

Our Urban Planet

As the human population balloons and cities sprawl, ecological studies in urban areas are following suit. Nature has always been a component of cities – we can’t escape it after all, as hard as we may try – but urban nature (and the enhancement of it) has become increasingly important as the human species continues to urbanize. More and more we are seeing the importance of melding the built environment with the natural one. Our motivations are diverse – albeit largely anthropocentric. But that’s fine. As we make improvements to the live-ability of cities for human’s sake, other living beings benefit. We are finding ways to get along with our neighbors, and we are learning to appreciate and value them as well.

Since 2008, the world’s urban population has outnumbered its rural population, and it is predicted that by 2050, more than two-thirds of humans will be urbanites. Immense resources are required to support such large, concentrated populations, and most of these resources are produced outside of urban areas. This results in an ecological footprint that is significantly larger than the city itself. Additionally, waste and pollution produced within cities negatively effects surrounding areas and beyond in abundant ways.

st louis

In May of this year, Science put out a special issue entitled, “Urban Planet,” which features a series of articles that address some of the latest research in urban ecology and discuss current developments and future research needs – a sort of state of the union address for urban ecology in 2016. A series of 13 articles covered diverse topics including city-integrated renewable energy, innovative solutions to water challenges, transportation and air pollution, and food security in an urban world. Rodent-borne diseases in urban slums, creating sustainable cities in China, and Vancouver’s push to become the “greenest city” were also features of this special issue.

The issue serves to highlight the importance of this field of study and the urgency there is in finding solutions to major environmental challenges. But it also offers hope. Bright minds are working towards solutions to this century’s biggest problems as we look towards a more sustainable future. The introduction emphasizes that “the rise of cities is not…all doom and gloom.” Urbanization has upsides: “consolidating human populations helps shrink our individual environmental footprints, and cities are serving as living laboratories for further improvements.”

Urban ecology is a relatively recent subfield of ecology. In The Ecological Future of Cities, Mark McDonnell and Ian MacGregor-Fors describe how it “arose in the 1990’s out of a need to increase our…understanding of the ecological and human dimensions of urban ecosystems.” Initially the field was mainly concerned with biodiversity and the ecosystem processes and services found within cities. Findings from these studies are now influencing urban planning, design, and management. Such decisions are also informed by more recent studies in the field of urban ecology, which has grown to include “issues of sustainability, environmental quality, and human well-being in urban ecosystems.”

The authors note that our ecological understanding of cities was waylaid because “nature within cites was long considered unworthy of study, except when it involved solving environmental problems that threatened human well-being.” Cities were perceived as unnatural because humans had “disrupt[ed] the natural ecological conditions and processes that scientists [were] attempting to understand.” Today, ecologists recognize that studies in the field of urban ecology help us better understand basic ecological principles, while also providing “valuable information for creating liveable, healthy, and resilient urban environments.”

Studies in urban ecology have also increased our understanding of the mechanisms involved in evolution and adaptation. To illustrate this, the authors offer examples of birds that modified their songs “to communicate at noisy locations” and plants that shifted their seed dispersal strategies to survive in “highly fragmented urban habitats.” The authors also highlight the importance of maintaining or restoring natural vegetation in urban areas in order to help preserve struggling species of plants and animals, citing a study that found that “fewer local plant extinctions occurred in cities that maintained at least 30% native vegetation cover.” Additionally, the authors note that “the scope of urban ecology research extends well beyond city limits,” since urbanization is partly to blame for numerous environmental issues including habitat loss and fragmentation, biodiversity loss, climate change, and invasive species.

In Living in Cities, Naturally, Terry Hartig and Peter Kahn, Jr. address the topic of mental health and urban living. While there is still much to learn about the relationship between the two, it is generally believed that viewing or spending time in nature can help improve one’s mental well-being. As the authors put it, “parks and green spaces” can be viewed as “health resources for urban populations,” and including natural areas and natural processes in the design and creation of cities is necessary “for psychological as well as ecological purposes.”

Green roofs

Green roofs are one way to add green space to urban areas. They help replace vegetation that was removed when buildings were constructed, and they offer numerous environmental benefits.

Interacting with nature in an urban setting can help people develop positive feelings about the natural world and may encourage support for environmental protection. The authors worry that if future generations grow up without an intimate connection to the natural world, elevated amounts of environmental degradation will be seen as normal and a feeling of urgency to protect the environment from continued degradation will fade. This is why including plentiful amounts of green space within cities is essential: “Providing opportunities for people to experience more robust, healthy, and even wilder forms of nature in cities offers an important solution to this collective loss of memory and can counter the shifting baseline.”

This special issue of Science highlights some of the current ecological and environmental research regarding urbanization. For a great introductory look at urban ecology and basic ecological principles, check out the book, Nature All Around Us. Also, expect to see many more urban ecology themed posts on Awkward Botany. Tell your friends.

Attract Pollinators, Grow More Food

It seems obvious to say that on farms that rely on insect pollinators for crops to set fruit, having more pollinators around can lead to higher yields. Beyond that, there are questions to consider. How many pollinators and which ones? To what extent can yields be increased? How does the size and location of the farm come into play? Etc. Thanks to a recent study, one that Science News appropriately referred to as “massive,” some of these questions are being addressed, offering compelling evidence that yields grow dramatically simply by increasing and diversifying pollinator populations.

It is also stating the obvious to say that some farms are more productive than others. The difference between a high yield farm and a low yield farm in a given crop system is referred to as a yield gap. Yield gaps are the result of a combination of factors, including soil health, climate, water availability, and management. For crops that depend on insects for pollination, reduced numbers of pollinators can contribute to yield gaps. This five year study by Lucas A. Garibaldi, et al., pubished in a January 2016 issue of Science, involving 344 fields and 33 different crops on farms located in Africa, Asia, and Latin America demonstrates the importance of managing for pollinator abundance and diversity.

The study locations, which ranged from 0.1 hectare to 327.2 hecatares, were separated into large and small farms. Small farms were considered 2 ha and under. In the developing world, more than 2 billion people rely on farms of this size, and many of these farms have low yields. In this study, low yielding farms on average had yields that were a mere 47% of high yielding farms. Researchers wanted to know to what degree enhancing pollinator density and diversity could help increase yields and close this yield gap.

By performing coordinated experiments for five years on farms all over the world and by using a standardized sampling protocol, the researchers were able to determine that higher pollinator densities could close the yield gap on small farms by 24%. For larger farms, such yield increases were seen only when there was both higher pollinator density and diversity. Honeybees were found to be the dominant pollinator in larger fields, and having additional pollinator species present helped to enhance yields.

These results suggest that, as the authors state, “there are large opportunities to increase flower-visitor densities and yields” on low yielding farms to better match the levels of “the best farms.” Poor performing farms can be improved simply by managing for increased pollinator populations. The authors advise that such farms employ “a combination of practices,” such as “sowing flower strips and planting hedgerows, providing nesting resources, [practicing] more targeted use of pesticides, and/or [restoring] semi-natural and natural areas adjacent to crops.” The authors conclude that this case study offers evidence that “ecological intensification [improving agriculture by enhancing ecological functions and biodiversity] can create mutually beneficial scenarios between biodiversity and crop yields worldwide.”

photo credit: wikimedia commons

photo credit: wikimedia commons

A study like this, while aimed at improving crop yields in developing nations, should be viewed as evidence for the importance of protecting and strengthening pollinator populations throughout the world. Modern, industrial farms that plant monocultures from one edge of the field to the other and that include little or no natural area – or weedy, overgrown area for that matter – are helping to place pollinator populations in peril. In this study, after considering numerous covariables, the authors concluded that, “among all the variables we tested, flower-visitor density was the most important predictor of crop yield.”

Back to stating the obvious, if pollinators aren’t present yields decline, and as far as I’m aware, we don’t have a suitable replacement for what nature does best.

This study is available to read free of charge at ResearchGate. If you are interested in improving pollinator habitat in your neighborhood, check out these past Awkward Botany posts: Planting for Pollinators, Ground Nesting Bees in the Garden, and Hellstrip Pollinator Garden.

Podcast Review: Gastropod

I am a voracious consumer of podcasts and have a long list that I regularly listen to. Despite being unable to get through all of them in a reasonable amount of time, I am still continually on the lookout for more. I am particularly interested in science or educational podcasts – something that I can listen to for an hour or so and learn new things about the world, whether it be breaking news or historical facts.

This year a new podcast was born – a podcast exploring the science and history of food.  It is called Gastropod, and it has quickly found its way into my regular rotation of podcast consumption. It wasn’t a difficult climb either, as the general theme of the podcast is something that fascinates me and the hosts do a top-notch job presenting the information and telling the stories.

gastropod

Gastropod is hosted by Cynthia Graber and Nicola Twilley, each of whom have impressive backgrounds in researching and reporting on science, technology, food, and other topics for a variety of outlets both large and small. Among numerous other projects, Nicola has a blog called Edible Geography and Cynthia contributes regularly to Scientific American’s 60 Second Science podcast. Gastropod just happens to be their latest endeavor, and it is a welcome one.

Full length episodes of Gastropod are released once a month, with “snack-sized interludes” called Bites released in between to tide listeners over until the next helping. Since Gastropod is in its infancy (the first episode was released in September 2014), catching up on past episodes is simple. An afternoon of binge listening will do it.

Topics covered so far in full length episodes include the history and evolution of cutlery (which involves a taste test using spoons made of various metals), a discussion with Dan Barber about his book The Third Plate, an exploration of the emerging “microbe revolution” in agriculture (which piggybacks on an article that Cynthia wrote for NOVANext and which I reviewed back in July), and the rising popularity of kelp (“the new kale”) and the growth of seaweed farms. Bite-sized episodes have discussed things like modern day domestication of wild plants, underused American seafood resources, a meal replacement drink called Soylent, the expansive yet underappreciated (and disappearing) diversity of apples, and subnatural foods (smoked pigeon, anyone?).

So far every episode has been great, but if I had to pick a favorite, the interview with Dan Barber really stands out. His discussion of “ecosystem cuisines” – which moves beyond the farm-to-table movement – was new to me but seems like an important idea and one that I would like to see play a pivotal role in the development of science-based sustainable agriculture.

Gastropod is a young but promising podcast, and I look forward to many more captivating episodes in 2015 and beyond. Learn more about Gastropod and its hosts here.

Do you have a favorite podcast, science-themed or otherwise? Share it in the comments section below.

Northern Pitcher Plant: A model for understanding food webs

Carnivorous plants are endlessly fascinating. Even people who aren’t typically interested in plants are likely to find plants that eat animals to be of some interest. These plants not only provide fascination for plant lovers and the plant ambivalent alike, but they are also of great interest to science, providing insight into the workings of the world beyond the swamps and bogs that they inhabit.

A recent study published in the journal, Oikos, examined the complex food web that exists inside the northern pitcher plant (Sarracenia purpurea) in order to come to a better understanding of food webs in general and to construct a model that will aid in further research involving food webs in all types of ecosystems.

The food web that exists inside a pitcher plant is quite interesting. The tubular leaves of the pitcher plant capture rain water and draw in a variety of insects including beetles, ants, and flies. The pool of water also becomes home to the larvae of midges, mosquitoes, and flesh flies, as well as various other tiny creatures including rotifers, mites, copepods, nematodes, and multicellular algae. And thus begins a complex food cycle. Midge larvae attack the drowning insects and tear them to pieces, then bacteria go after the tiny insect parts, after which rotifers consume the bacteria. Finally, the walls of the pitcher plant absorb the waste of the rotifers. Meanwhile, fly larvae consume the rotifers, midge larvae, and other fly larvae, while bacteria is being consumed by all participants.

You can see why this food web is an ideal subject of study. Not only is it complex, with numerous players, but it is also all taking place in a small, confined space – easily observable. By studying such a system, models can be derived for larger, more widespread food webs.

Carnivorous plants have diverse mechanisms for extracting nutrients from other living things – this is just one of those mechanisms. I will plan to profile other carnivorous plants on this blog, because like I said, they are endlessly fascinating. Meanwhile, you can read more about this particular study at Science Daily.

northern pitcher plant

northern pitcher plants (Sarracenia purpurea) photo credit: wikimedia commons