Summary:
Class Discussion (NCSU)
We began class by reviewing the two articles by Marzluff (2005) and Hope, et al. (2003). Here are some of the highlights and big questions.
  • We started with a review of the basic concepts of island biogeography, and examination of how Marzluff applied the processes of colonization and extinction to 1 square-km plots in Seattle, even though they are not literally islands.
  • Marzluff’s observations that support the intermediate disturbance hypothesis could be influenced by some site-specific factors. They include a reservoir of native species in natural areas around Seattle and a lack of competition between native forest birds and synanthropic birds.
  • Hope, et al. use the term “invasive” but Marzluff does not. How do you define invasive? Is anything actually native to an urban environment, and therefore can anything be invasive there? How does public perception [[#|apply]]? We had lots of questions along this line, but few answers.
  • In urban environments, animals can be grouped into exploiters, [[#|adapters]] and avoiders. We had a good story of a neighborhood conflict, which illustrated how perception of chickens, hawks and opossums affects how people interact with them.
  • Even though the intermediate disturbance hypothesis suggests that bird diversity is greatest at moderate levels of development, there are species that will only exist at extremes of development. Therefore, diversity on a larger scale would actually be reduced if it was maximized within every smaller unit.
  • McKinney (2008) summarized past studies to show that the intermediate disturbance hypothesis is not clearly supported for many types of animals. Perhaps it works for birds and plants because humans sometimes actively manage for them.
  • Hope, et al. demonstrated a luxury effect in Phoenix, but again, are there site-specific influences that may not hold true elsewhere? In a desert region, the observed diversity requires inputs of water and fertilizer and human cultivation. A study performed by a class member in Puerto Rico found no luxury effect, but instead found species diversity linked to education and age of homeowners. Also, in a past class we saw that immigrants in Miami cultivated plants native to their homeland in their back yards. Could that diminish or even reverse the luxury effect in Miami?
  • We examined the question “is biodiversity desirable?” There was an example of how humans planted lots of elms in cities, and then Dutch elm disease wiped them out. Increased biodiversity may or may not relate to increased ability of an ecosystem to adapt to changing conditions.

Class Discussion (BU)
We began finishing off the lecture from last week about carbon cycling in urban systems:
  • [[#|Carbon sequestration]] by urban vegetation plays an almost negligible role in urban metabolism; in at least two example systems, ~1/10th of the vegetative carbon sink is emitted in fossil fuels every year. However, removing urban trees does substantially alter the carbon cycle. This is in large part due to the changes in time lags when carbon is removed from sinks. For instance, while clearing a forest to plant corn may appear to replace one carbon sink with another, the carbon sequestered by a corn field has a dramatically different time lag before release than carbon in a forest.
  • Urban development is projected to occur in areas that currently contain the world's largest carbon sinks (e.g. tropical rainforest), and that deforestation, land cover and land use change will alter the carbon cycle on a worldwide scale.
Deforestation is not the only way urbanization alters the carbon cycle-- paving alters the hydrology and permeability of soils, decreasing the soil carbon sink. Carbon is able to leave paved-over soils through water or cracks in the pavement much faster than carbon can enter the soil through that same pavement. This can result in urban flooding and changes to carbon and nutrient levels in urban soils.
  • Professor Hutyra and her team performed a study in the Bronx and Brooklyn, NY (paved ~100 years ago) to measure the amount of carbon in soils under pavement and in reference plots (no pavement). Paved samples were gathered from soils exposed during urban tree planting. They found that paved soils had 60% less carbon than reference plots and contained NO nitrogen, the limiting nutrient for trees in the Northeastern U.S. The carbon lost from these paved soils has likely been released back into the atmosphere.
  • If we scaled Prof Hutyra's findings to the entire United States (113,000 km2 impervious surface) that means we have lost ~620 tg of C. With lawns estimated to sequester ~400 tg C, this makes the land use change of cities a net carbon loss.

Presentation: Dr. Paige Warren- Biodiversity in the City: Ecology, Evolution, and Behavior (NCSU and BU):
  • Most study of urban biota has been on birds in temperate zones in the northern hemisphere. There are lots of research gaps for us to fill.
  • Rather than just examining remnant patches of forests, woodlands, marshes, etc. within a city, we can examine residential areas directly.
  • As an area becomes more urbanized the biodiversity will eventually decrease, but the population density will increase in the species that are still left (although the shapes of those curves are not always clear).
  • An example from Phoenix demonstrated the spatial arrangement of an exploiter (pigeon), and adapter (cactus wren) and an avoider (Phainopepla). It showed that some native species can adapt better and penetrate closer to city center.
species urban curves.JPG

  • Differences between species in behavioral responses to urbanization may lead to shifts in community structure. Some examples include:
    • Species that can increase the pitch of their auditory communication above the background noise may reproduce better.
    • Some urban birds (as demonstrated with Acadian Flycatchers) are less likely to return to a nest that has been predated, even though predation rates are the same as in woodlands.
    • Urban birds may be able to breed earlier, because of the reliable and nutritious food supply discarded by humans.
    • Other behavioral shifts include changes in home range, time of activity during the day, movement (such as roadside avoidance), anti-predatory behavior (vigilance), body size and diet. Dr. Warren urged us to consider the behavioral mechanisms behind dispersal limitations and settlement biases within the colonization-extinction framework.
  • In residential areas, vegetative structure and composition varies considerably, even among sites with similar housing density. Therefore, the urbanization gradient alone isn’t telling us everything we need to know.
  • The spatial structure of a city can be divided different ways. You can look at functional groups, status groups, or cultural groups.
  • The Kuznet curve shows that per capita pollution rises with income, until at some point it declines.
  • Looking at bird diversity and social stratification, we see that species richness per parcel increases with family income in cities like Phoenix, where lot sizes are almost identical and are mostly single-family homes. However, we see the opposite relationship in Chicago.
  • In residential areas we see many different land managers with tiny pieces of land. Their decisions can be influenced by lifestyle and prestige and landscaping companies.
  • One study divided yards into categories: xeric (dry) and mesic (wet). Researchers found that the factors that most influenced bird communities local vegetative variation, followed by socioeconomic status, followed by urban-rural gradient.
  • Spatial autocorrelation shows that people tend to do what their neighbors are doing in terms of landscaping. Can we harness this effect? (e.g., home owners’ associations)
  • Looking at natural selection and plant-insect interactions, we see that there are antagonists who steal nectar without pollination and mutualists who pollinate when they take nectar. A study hypothesized that with increased density of antagonists in urban areas, the plant will work harder to repel them than in forested areas. Results looking at the influence of gardens showed that there was a change in species interactions in association with socioeconomic variables.

Question and Answer Session (NCSU and BU):

Do older cities show the same species-richness curve that peaks in the middle as predicted by the intermediate disturbance hypothesis?


    • The shape is influenced by the scale of measurement, and ecoregion also determines shape.

How does feeding birds impact biodiversity in an urban environment? Do we owe it to them since we removed their original food sources? What are the pros and cons?


    • It can attract raccoons and squirrels that eat the birds’ nests.
    • Depending on what you feed them , they may become dependent on feeder for food source, which may have cascading effects down the food chain, such as insect populations
    • Maybe it’s better to offer food targeted at certain species, such as migratory hummingbirds.
    • Evidence shows that when you feed birds, it doesn’t cause them to delay migration long enough that they die from the winter.
    • Most adult birds don’t bring feeder food to their babies, although gulls and woodpeckers are exceptions.
    • People are engaged by birds at their feeders, promoting connection with wildlife.
    • Does it take away from other ecosystem services that birds provide in terms of pollination and seed dispersal? Maybe we are stealing pollinators, or maybe we are supporting additional pollinators.

Are there other divisions of birds besides those in the Marzluff paper?


    • What makes an urban bird? No clear answers so far.
    • With increased data, we can compare across cities and see what are the different strategies for becoming an urban bird. This may include birds whose natural nesting habitat can be recreated by a feature in the city (such as rocky hilltops, replaced by rocky rooftops).

Do we have examples of speciation of urban and non-urban versions of animals?


    • Suppose feeding caused a population to separate and develop different migratory patterns, leading to morphological divisions and different songs. The birds could develop a preference for songs from their own kind, which could promote reproductive isolation. However, since songs are learned, a bird that leaves the city could adapt its song to the wildland population and reproduce anyway. One overwintering population of Oregon Junco in CA has begun to develop different tail morphology from the migratory population.
  • Is biodiversity positive? What about in the example of Phoenix where you have to invest water and fertilizer to enhance biodiversity in the desert?
    • Paige suggests that we manage for species that are regionally distinct rather than managing for total diversity. That way we enhance biodiversity at a larger scale.

The Questions and answers continued at BU:
  • Following Dr. Warren's presentation, the question was also raised in our classroom: "what is the value of biodiversity in urban systems, particularly considering that urban landscapes don't seem that fragile?" One answer to this question was that it is important to consider the different magnitudes of effect that a single species can have within an ecosystem (and the ability of one dominant species to completely change the structure and function of an ecosystem). Macquarie Island in Australia, colonized in 1810, is one such example of disturbed ecological balance. The indigenous fauna such as seals were killed for their blubber, and human colonizers introduced rats and mice from ships. Because of the lack of predators, the rodent populations grew rapidly. So, cats were introduced to the city to consume the rodents. In 1870, rabbits were left on the island to breed for food, and caused tremendous damage to vegetation. Meanwhile, cats decimated local seabird populations breeding on the island, so the government eliminated the cats, which allowed rodent and rabbit populations to explode. Eventually, the Australia government put $24 million into eliminating rats and rabbits. The Australian reported in 2012 that rabbits, rats and mice had been nearly eradicated from the Macquarie Island.
  • One student asked Dr. Warren how she felt about scientists as advocates and what her role was in advocacy. She seems very committed to conducting studies that have management implications, and said she often considers whether her work will be of use to developers and land managers when asked scientific questions and designing studies. She suggested that scientists are most efficient when they connect with brokers within the community who can turn science into curriculum, policy, and disseminate findings to the public.
  • We learned that Dr. Warren has a gang of volunteer point counters who conduct urban sampling, and that this is one way to harness the people power that cities provide. We briefly discussed the difficulty with using citizen science projects like eBird, as the observations that citizen scientists submit can be hard to normalize by observer effort and complicate statistics.
  • We spoke with Dr Warren about how we might freeze a city right in that sweet spot, where biodiversity is at its peak, and whether that is even a possibility. We discussed this as a class, and while we considered that you might be able to limit land use change after a certain point and plan for landscape heterogeneity, urban systems are also extremely dynamic, and some processes (such as the spread of invasive species) are trajectories that are difficult or impossible to interrupt.
  • We also talked about evidence for genetic divergence of bird species in urban systems. There have been some studies that show some differences among finches in urban and non-urban areas.


Blogs:

Toby Fusco - I feel that this week’s readings and Paige Warren’s presentation complimented each other very well. The subject of urban organisms was a very interesting topic. The role of birds in the urban environment was a much larger topic than I expected. The presence of birds and how humans feed them and interact with them was enlightening. The Hope et al. and Marzluff papers were both informative and easier to follow than some of the past assigned papers. These papers seemed to be more research-based and less in the way of conjecture and opinion. For me, they helped illustrate some of the relationships between socioeconomic traits and the urban environment we have discussed in the past few classes.

For a few weeks now, we have talked about how there seems to be a relationship between wealth/affluence and plant species diversity. The Hope et al. paper put some prove behind this statement. One thing I found interesting about this paper was how the authors concluded the relationship between elevation and development of neighborhoods. They discussed how the areas of higher human development also had higher diversity in plant species. Many of these plant species were brought in and planted by homeowners.

The fact that people seem to flock to higher location in major metropolitan area in the United States was an interesting thought. There could also be a correlation between higher elevation and overall plant diversity. I use the following diagram in my Global Biogeography lecture in Physical Geography courses I have taught in the past. This image comes from Introducing Physical Geography – 5th Ed., Alan H. Strahler, John Wiley & Sons, Inc., 632 pp., 2011. This example is from a Sonoran Desert ecosystem which fits well with the Phoenix, Arizona example discussed in Hope et al. This diagram shows altitudinal zonation in this particular ecosystem. The lower elevations are more arid than higher elevations. As you increase in elevation, temperatures decrease and as temperatures drop you are more apt to reach saturation. When air is saturated, clouds are more likely to form and precipitation can eventually fall. Climatically, higher elevations have localized heavy annual precipitation (mostly in the form of snow).


zonation.png


I thought this was an interesting idea to add to what the authors already discussed. In this case, homeowners in Phoenix have built homes, yards and gardens and brought in plants to an area that naturally has higher annual precipitation than lower elevations. Whether this was part of the planning process or a coincidence is unknown. Either way, a very important abiotic component needed for all ecosystems is readily available at higher elevations and this could possibly add to the higher plant diversity in neighborhoods at higher elevations.

Mustafa Saifuddin:
After the last two classes’ focus on some abiotic, social and theoretical aspects of urban ecology, I was very excited to hear about how some basic community ecology principles operate on biota in urban ecosystems! I was particularly interested in the behavioral shifts which allow some generalist bird species to habituate to novel environments in urban settings. Both Paige Warren and the Marzluff paper relied on some qualitative, predictive graphs modeling species richness (like the intermediate disturbance hypothesis) or competitive interactions (generalist and specialist fitness along a rural to urban gradient). It seemed that birds in urban settings illustrated these predictions elegantly! I started thinking of other predictions one might have based on these basic community ecology ideas, and I wonder how the relatively higher density of generalist bird species in urban areas partition niches to be able to coexist. We saw some evidence of spatial segregation with the heat maps showing different species in different parts of a city, and behavioral shifts suggested there might be temporal niche separation based on foraging time. I wonder if the generalist species become more specialized in their diet, which might then eventually lead us to reclassify them as specialists. I would only hypothesize feeding specialization if there is heightened competition in urban areas due to higher densities of birds occupying a similar niche, but there was also a surprising suggestion that competition may be reduced in urban settings due to more stable availability of low-quality food (i.e. “Credit Card Hypothesis”).

During the discussion, someone raised a question about the potential for urban and rural bird populations to diverge genetically. Given the slides on plant-pollinator networks at the end of the presentation, I was reminded of an interesting study showing that impervious cover is actually associated with increasing genetic differentiation between bumble bee populations! I imagine this question is much easier to assess in bees due to low genetic variation within colonies and very high population numbers, but I too wonder if similar patterns might arise in urban bird species, especially if they exhibit behavioral changes to occupy urban niches.

Scott Beck:
Echoing Mustafa's sentiment, I thought it was really nice to shift gears and focus on urban biota. I'm keenly interested in the idea that urbanization is a catalyst for evolution, and I really like hearing from experts who can cite specific examples. The backyard feeding discussion was also intriguing, and it got me thinking about if/when learned behavior sparks evolutionary changes in urban species. For instance, the backyard feeding of birds no doubt increases predation around feeders, which in turn forces adaptations in prey species. Both predators and prey are 'learning' in a uniquely urban context.

This discussion also had me thinking about how urbanization/disturbance can facilitate invasion. One of my classmates who does really interesting work with scale insects found that the urban heat island is a driver of scale insect abundance on urban trees. Also, we have done some work that suggests that patterns of urbanization and land cover can predict fire ant dispersal/habitat. I'm sure there are similarities between pest invasion and the prevalence/abundance of other urban adaptive species. I also wonder about how well the intermediate disturbance hypothesis would hold up in urbanized areas in the tropics, where species abundance is much higher than in the US. Melissa showed us a paper that demonstrated that the IDH generally held true for bird & plant species in the US, but not for other vertebrates. Basically, species in urban areas compete for 'our' attention, and those that we value the most contribute to urban biodiversity -- others are either ignored or intentionally irradiated. Anyway, it was nice to get out of my little abiotic/urban spatial patterns box for a bit and think about the biology of cities for a little while.

Evan Kuras:
As an undergraduate interested in urban ecology, I found Paige Warren's dynamic talk quite inspiring. She mentioned the idea of the "frontier" numerous times and how this relatively new field is just brimming with new ideas and unexplored avenues. Echoing this sentiment, I was surprised by the tone taken by Marzluff at the end of his 2005 paper. Read portions of his last paragraph here:

"Urban ecologists will increasingly require interdisciplinary training to understand how policies are formulated and implemented, how planners design landscapes, and what people want from their immediate surroundings... Students must open their eyes, ears, and minds widely. International travel is increasingly important. Take the window seat and look at patterns of development. Ask whether the patterns below you provide local, regional, and global diversity. Learn about foreign policies and value systems that seem to result in diverse landscapes. Help globalize knowledge so that we do not continue to do the same thing everywhere."

I underlined the two sentences that surprised me most. Maybe I have not read enough scientific papers, but I am not accustomed to receiving advice about how to live my life. I initially bristled at Marzluff's tone - at some level I believe ecology should be about studying what is actually there, not about prescribing the way things should be. Is it really so bad to do the same thing everywhere? Yet I agree with Marzluff and have heard "Take the window seat" repeated by other urban landscape ecologists. Urban Ecology is a new field and, like any pursuit of this nature, needs its leaders to set the stage for young exciting students like me.

Sravya:

Today’s class was my favorite thus far. I was very excited to meet Dr. Warren and discuss organismal ecology. I was really fascinated by Dr. Warren’s discussion regarding microevolution in urban areas. I was not aware that so many variances already exist amongst urban dwelling organisms and their wild-type counterparts.

What really had me thinking was the changing directionality of characteristics between desert and urban house finch, which seems to mirror the Darwinian paradigm of divergent evolution. There appears to be a left skew in morphological features (due to some selective pressure) such as beak length, depth, and width in the urban populations; moreover, this overall larger beak size is correlated with altered mating calls, a potential pre-zygotic barrier. It is amazing to think urbanization may result in speciation, and perhaps in turn, increase species diversity in urban areas. I wonder how this potential speciation will play out in the long run, both in terms of interspecies and interspecies competition. Furthermore, I wonder if there is a need/ way to control such rapid divergence.

Finally, returning to the discussion regarding bird feeders, I was reminded of a lab I did in introductory biology. To summarize, we took a field trip to Hammond Woods, MA to examine niche partitioning between different bird species at different bird feeders sites. Over the years this lab has been conducted, it has been found that resource partitioning does exist in terms of different habitat preferences as well as displayed aggressive behavior among the bird species. Perhaps backyard feeders can also induce a similar level of competition, which may have significant consequences in terms of what species will be the dominant feeders at these feeders, the levels of species diversity at these feeders, etc.

Amanda:
I was really delighted by Paige Warren's visit. I've spent several years monitoring birds in rural places- primarily national forests and the national seashore in CA. When I moved to Boston, I expected that my birding fun would take a huge hit. When I wanted to see birds, I thought I would have to leave the city, or at least find the green spaces in the city that "good birds" might be stranded in. Last Friday after Dr Warren's talk, I saw a flock of migratory warblers, including two Bay-breasted Warblers and a Prairie Warbler, in the strip of trees outside my apartment in Brookline. And that has been the most exciting part of this course for me-- discovering that urban ecosystems ARE ecosystems. Birds in downtown Boston are subject to the same rules as they would be in a national forest: they have to eat, they have to breed, they have to avoid predators and migrate. To echo some of the sentiments above, it was satisfying to see some qualitative modeling of diversity applied to urban ecosystems. I especially appreciated Dr Warren's focus on how the urban context influences not just species richness, but also behavior, and that behavior is a strong driver of richness. Even though they aren't especially thrilling species, I am really coming around to the value of observing birds like American Robins and House Sparrows- species that are clearly thriving in urban ecosystems- to start to make a mental list of 'what makes an urban bird'. As urban regions continue to expand, and songbirds are increasingly faced with this new type of ecosystem, having an idea of what might make an urban bird most successful will help us predict which species might transition well into an urban landscape, and which species and habitats to prioritize for conservation (those iconic specialists that may not transition well into urban birds).

Since 9/10 times it is a huge pain that birds move as much as they do (mostly for sampling purposes), it was exciting to hear Dr Warren use this as an advantage- we can observe bird behavior, and since birds can up and move pretty easily, they help us view urban effects quickly! Someone posed a great question (was that you, Evan?) about whether Marzluff was being paranoid about global homogenization. Sometimes I am tempted to treat broad statements based on theory as totally separate from my own observations-- but it seems really unreasonable based on what I've actually observed traveling around and paying attention to birds. Despite being able to pick up and go (to a certain extent), birds do maintain regional boundaries! Does anyone know if this is more of a concern for plants, insects, microbes?

Cool post, Toby!! It is really neat seeing how everyone's areas of focus fit into this big interdisciplinary framework. This seems like a big part of what made our discussion last Friday so exciting and productive!

Steve:
Amanda, I think that local homogenization is made to be more of an issue in terms of plants (regional homogenization sometimes happens naturally as a consequence of succession - think eastern hemlock forest) but again, it depends on who you're talking to. For example, systems with hydric soils that used to have more diverse plant communities are now, in large part, dominated by Phragmites australis (phrag, henceforth). This invasive is seen as a pestilence by many, not the least of whom are waterfront landowners who did not count on having a fifteen foot obstruction of their view when they bought their properties (I have a friend who has property on Lake Michigan whose neighbor dumps gasoline on phrag it and burns it). But phrag performs many ecosystem services at least as well as the plants that it replaced, and birders like yourself have told me that they love it because it attracts different types of birds.

The ripping great thing about urban ecology, in terms of plants, is diversity! The wacky disturbance regime, along with special soil, climate, and hydrologic conditions provide niches for some eclectic and beautiful plants. This picture

Living herbarium.JPG

is of the urban plant "living herbarium" that my students made this summer, and this is just a small fraction of what you can find growing in the city. And the coolest part - the less-affluent areas in NYC have the richest wild urban plant diversity! I would go on walks with the kids in midtown Manhattan and we would stop and "ohh and ahh" at the few refugee lambsquarters or pepperweed that had escaped the eyes of the ornamental plant propagators who had no respect for the wild urban stuff. But what the kids could bring home from the Bronx, Brooklyn, and Queens, found in abandoned parks and vacant lots, was truly spectacular. If anyone has time, go to the Arnold Arboretum and check out the Bussey Brook Meadow. What grows in there, largely, is what has recruited in there, and the Arboretum is intending on keeping it that way. So if you're worried about homogenization, worry about kudzu or Japanese stiltgrass in the forest, but I have confidence that our urban centers will be bastions of plant diversity for some time, especially as long as there are areas that find ways to resist corporate colonization.

Janet Felts: Just to reiterate what everyone has already said, it was a very special and unique experience to have Paige Warren speak to our class last Friday. I thought it was a nice change to switch from urban systems and urban metabolism towards something that everyone has a particular interest in- birds. Our discussion on whether it was okay or harmful to feed birds was especially intriguing as my thoughts immediately went to my mom. She has a ton of bird feeders in her yard at home, all specifically for hummingbirds and I had often wondered what these birds would do if she wasn't feeding them. But after hearing from Dr. Warren I am more hopeful that my mom's actions aren't actually harming these birds in the long run by making them dependent on her feeding them. They do seem to rely on her a good bit though, they even come to the kitchen window and seem to look inside when the feeder is empty and mom always knows that it is time to refill it. As Scott expressed earlier, all birds are learning new behaviors, not just the predators. The hummingbirds learned where my mom is to "tell" her that the feeder is empty. It is a unique experience to have these birds communicating to you in their own way. In my opinion, that is what makes our relationship to birds, or any animals, that much more important and special.

Michelle Predi:

I personally really enjoyed the very conversational approach that our talk with Paige Warren took on. I feel that it allowed us to really take the conversation towards what interested the group the most as a whole. Evolution and role that urban ecology plays in this realm was brought up in various ways. The concept of the "ideal city bird" was brought up, and that immediately brought to mind for me the image of a pigeon. I thought to myself that although a pigeon is the quintessential city bird from New York through Paris, the bird obviously was not always a city bird. This lead me the following NY Times article:
http://www.nytimes.com/2013/02/05/science/pigeons-a-darwin-favorite-carry-new-clues-to-evolution.html?pagewanted=all&_r=0.

The article claims that finding a truly "wild" pigeon, is no easy task, because humans have interacting with the species for so long in so many ways. However, current research in the genetic variations of 40 species of pigeons is giving scientists a better understanding of how such variation came about, and what driving factors of created today's "ideal city bird". Although cities are forever changing, therefore changing evolutionary drivers, I feel that one of the best ways that we can begin to better predict how birds of this day and age will adapt to cities is by examining how species that we currently consider city exploiters have evolved over the ages to be this way. The same holds true for other creatures such as typically exploit the cities.

Katy Lawless
I really enjoyed Paige Warren’s discussion. It was a nice change of pace to talk about birds since you see them every day. Dr. Warren’s presentation has definitely changed my view of birds in urban environments and the impacts urbanization has on them. Similar to what Amanda said, I don’t think of cities having nice birds. I am not a bird watcher, but when I think of birds in cities, I think of pigeons. This presentation made me realize that there is a lot of biodiversity in bird species in urban areas. Since our discussion I have become more aware of the different types of birds I see when I’m walking around Boston. I was interested in learning about how human impacts have changed the behavior birds, especially the changes auditory communication to compete with traffic noise. It always amazes me how much animals adapt to overcome human impacts.

I also thought our discussion about feeding birds was particularly interesting. When the topic was first brought up, I was thinking about people throwing bread crumbs on the ground, not bird feeders in someone’s yard. People feeding bread to birds aggravates me because bread does not provide any nourishment for them. I never thought of bird feeders as having a potential negative impact on birds in terms of making them dependent on humans for food.

Rene Valdez
As someone who has studied wildlife for a majority of their collegiate career these readings and lectures were a welcome change. But reading about wildlife in urban environments is relatively new to me. The examples I am familiar with tend to revolve around human-wildlife 'conflicts'. The influx of deer into urban environments and the emerging idea of a social carrying capacity, the dangers that mountain lions can pose in California, and elephants trampling fields in Africa are some of the most memorable examples.

But fauna that perpetually exist alongside humans in urban environments has not been my focus before. The idea of homogenization of both flora and fauna in urban environments is both fascinating and perhaps a little worrying. This homogenization could potentially lower biodiversity of urbanizing locales. While Marzluff presents data that shows higher biodiversity in mixed urban-forested environments I can't help but consider biodiversity losses on larger scales. The study in Washington does not take into consideration birds that migrate or birds that are rare in lower elevations. I assume that is because there is a low likelihood of ever counting these species. But that doesn't mean that the study areas are not or have never been important for these species. Many migrating birds needs resting areas to complete their migration. This leads me to questions of the effect of urban environments on species that range over extremely large or changing areas.

Eric Thompson:
You all have had a great many insightful comments and questions about Paige Warren’s class. I’ll take a different angle and offer a story instead:

A few weeks ago I was walking behind a gas station in Raleigh, when I happened upon a bit of a surprise. I turned the corner to see a squirrel dragging half a slice of pizza across the pavement, and there were 3 crows surrounding him and trying to take the food. They were so absorbed in the conflict, that they hadn’t heard me coming; I was less than 10 feet away. When the animals saw me they all froze for a fraction of a second--like when mom opens the door on a pillow fight. After a hasty assessment of the situation, everyone dropped their hold on the pizza and rushed off in terror. It was hilaaaaarious!

In class, Dr. Warren asked the question of “what makes an urban bird,” and said there was no clear answer. To me, the scene I saw behind the gas station answers at least part of that question. You have access to much more reliable and much richer food sources, but you have to put up with more competition, and you have to be able to negotiate the giant, unpredictable, 2-legged monsters that live there. It’s actually remarkably similar to the same factors that make an urban person.

I also stumbled across an article by Levey et. al. (2009) that was seeking to answer the question of why some urban species adapt well to humans and others do not. They found that mockingbirds could differentiate a single student who threatened their nest from thousands of other individuals walking by on the campus of the University of Florida. The researchers came to the conclusion that “the varying responses of mockingbirds to intruders suggests behavioral flexibility and a keen awareness of different levels of threat posed by individuals of another species: traits that may predispose mockingbirds and other species of urban wildlife to successful exploitation of human-dominated environments.” (p. 2)