Defining the habitat of an organism is key to understanding
its role in the environment and how it interacts with other species. In a
general sense, habitat is the space in which an organism or group of organisms
lives. More finely, habitat is often defined based on the dominant vegetation of
an area. However, defining habitat in this way does not always accurately
represent species densities or even their overall presence or absence. Another
approach to defining habitat is the resource based model, which accounts for species-specific
essential resources and environmental conditions rather than general vegetation
type alone. For mapping species’ local distributions, this approach may be more
accurate than the vegetation-based model.
In their study,
Vanreusel and Van
Dyck tested the resource-based approach against the vegetation-based approach
using green hairstreak butterfly (Callophrys rubi) populations in a heathland landscape. The researchers generated both
a vegetation map and a resource map including variables such as nectar plants,
mate-locating sites, shelter, microclimate, and host-plant availability (fig.
1). Observations of C. rubi were
recorded in two consecutive years using GIS. The proportion of observations explained
by the resource-based approach was significantly larger than in the case of the
vegetation type approach (1466/1724 versus 954/1724, Fisher’s Exact Test, p < 0.0001).
Even for highly mobile organisms on a landscape scale, the resource-based model
can more successfully define the actual habitat of a species.
Figure 1) (a) Vegetation map
(dark green and pale green: pine forest; bright green: broad-leaved forest;
pink: dry heathland; purple: wet heathland; yellow: Molinia dominated
moorland; orange: Myrica shrubland; blue: open water. (f)
Habitat suitability zones for larva and adult C. rubi based on resources. Figure courtesy of https://doi.org/10.1016/j.biocon.2006.10.035.
A resource-based, rather than a
vegetation-based, model for defining habitat is useful in urban environments.
Urban environments are highly fragmented, so using vegetation alone as a
determinant of habitat is too coarsely grained to define habitat. In our urban
Ecology project, we will use vegetation/substrate type as an explanatory factor
to the distribution of fungi on Grinnell’s campus. However, we also need to consider
other essential resources for fungi, such as moisture availability or shelter
from disturbance to fully be able to explain variation in fungal density. We believe this resource-based approach would best explain fungal density variation because of the highly fragmented nature of Grinnell's campus.
Reference:
Vanreusel, W., Van
Dyck, H. (2007). When functional
habitat does not match vegetation types: A resource-based approach to map
butterfly habitat. Biological Conservation, 135(2), 202-211.
https://doi.org/10.1016/j.biocon.2006.10.035.
Unfortunately, many people have a negative opinion, or a general indifference, towards fungi. They infect and lessen the yield of wheat. People believe that every other mushroom in the wild is deadly or poisonous. Even the edible mushrooms are slimy and gross in texture. Most individuals’ favorite interaction with fungi is kicking the unsightly mushrooms on their lawns as a kid. While often overlooked, fungi play a variety of different roles and are often crucial to a functioning ecosystem. Fungi can be parasites, attacking the weakened defenses of animals and plants; decomposers, taking dead material, breaking it down, and making nutrients available to microorganisms and plants; mycorrhizal, associating with plant roots-- mostly trees -- and exchanging nutrients in a mutually beneficial relationship. These are only a few examples of how the important fungi are to the ecosystem. Fungi are an underappreciated and vital part of many functioning ecosystems in varying locations.
Another part of ecology that deserves more attention is urban environments which are ever increasing in today’s world. They are alive with organisms from trees lining the street to raccoons scurrying around at night. While more and more people are studying the ecology of these ecosystems, much more work needs to be done for this rapidly growing ecosystem.
In a recent study, Bainard, Klironomos, & Gordon (2011) sought to compare the abundance anddiversity of mycorrhizal fungi in urban versus rural areas. Past research has shown a decrease in mycorrhizal fungi abundance in urban areas in comparison to rural areas in some habitats such as deserts (Stabler et. al. 2001). Bainard, Klironomos, & Gordon (2011) continued this research by studying 26 different species of trees in southern Ontario. In order to measure the abundance of mycorrhizal fungi, the researchers took soil cores from underneath the trees and looked for ectomycorrhizal fungi at the tips of roots. The researchers also stained and examined small sections of roots in the soil cores for microscopic arbuscular mycorrhizal fungi. Bainard, Klironomos, &Gordon (2011) found that while all trees in both environments have mycorrhizal fungi, trees from urban areas statistically have significantly less than their rural counterparts (Fig. 1).
Fig. 3 All 26 tree species average mycorrhizal associations in rural versus urban environments. Asterisks indicate a significant difference between urban and rural environment bars below them (p=0.05) (Bainard, Klironomos, & Gordon, 2011).
Bainard, Klironomos, & Gordon (2011) stress the need to study more about what causes this decrease in abundance — theories include increased disturbance, fragmentation, and pollution -- and what can be done to increase the abundance of mycorrhizal in order to have healthier trees in urban settings.
Bainard, Klironomos, & Gordon’s (2011) study is important because some of the mushrooms we recently sampled as part of a Grinnell South Campus mushroom survey havemycorrhizal associations with trees. Figure 2 shows Xerocomus ferrugineus, a mycorrhizal bolete similar to some of those found on the east side of the South Campus dorms.
Figure 2. Xerocomus ferrugineus is a mycorrhizal bolete that associates with conifers and hardwoods throughout northern Europe and North America. (Kuo, 2016)
These fungi are important for the health of trees that add beauty to our campus. We know from studies like Bainard, Klironomos, & Gordon’s (2011) that fungi are not as prevalent in urban environments and they have several theories for why this is. We are trying todiscern where the fungi are present in urban areas, such as the less disturbed areas on the east side of South Campus. Then, we can try to replicate these conditions to allow fungi to thrive throughout the campus. Therefore, we should have healthier trees and lawns that we cherish so much thanks to decomposing and mycorrhizal fungi making nutrients more accessible.
References
Bainard, L. D., Klironomos, J. N., & Gordon, A. M. (2011). The mycorrhizal status and colonization of 26 tree species growing in urban and rural environments. Mycorrhiza, 21(2), 91-96.
Kuo, M. (2016). Xerocomus ferrugineus. Retrieved from the MushroomExpert.Com Web site: http://www.mushroomexpert.com/xerocomus_ferrugineus.html
Stabler LB, Martin CA, & Stutz JC (2001) Effect of urban expansion on arbuscular mycorrhizal fungal mediation of landscape tree growth. J Arboric 27:193–202
Review on Bird communities and the structure of urban habitats
“Okay,” I said. Then I thought of something, all of a sudden. “Hey, listen,” I said. “You know those ducks in that lagoon right near Central Park South? That little lake? By any chance, do you happen to know where they go, the ducks, when it gets all frozen over?
Ecologists have been focused on the distribution and richness of a species in the natural environment for a long time. How organism lives in their natural habitat has been intensively studies. Recently, with the rapid urbanization, ecologists have started to focus on how organisms live under the urban environment, a relatively “unnatural” environment for most of the organisms. Understanding how urban settings influence the dynamic of population helps the preservation of urban species. The urban environment brings both challenges and opportunities for the creatures it hosts. A studies from Lepczyk et al. (2017)[1] shows that artificial green space is the major habitat for most of the urban species. Different from “natural” habitat, the urban green spaces, usually separated by artificial construction, are more fragmented and disconnected. The fragmented green space prevents organisms from switching between different types of green space and maximizing their fertility. Under the “natural setting,” where habitats are usually connected, one organism could choose a habitat with more resources during the growing season and then transport to other habitats with less competition to lay their eggs. The prohibition of habitat choice decreases the total fertility of each species and therefore fails to maximize the potential of urban habitat. However, for our focus species today, birds, their high mobility allows them to switch between habitats with ease. Therefore, the habitat bird chooses is aligned with their will, which maximize the urban habitat benefits. By taking a close look at the population dynamics of bird species, one can see how they relate to the structure of the habitat.
In a paper by Lancaster and Rees (1979)[2], the authors explore how environment structural influences the overall diversity, richness, and density of individual species. They collected data by surveying the abundance and diversity of bird species under different habitat settings. The authors divide the habitat they surveyed into five major categories (i.e., commercial industrial, apartment, suburban, woodland, and rural) by both artificial construction coverage and foliage. The main finding from the study is that the foliage coverage is a positive indicator of bird species diversity while the artificial construction coverage is negatively correlated with bird species diversity. One interpretation (Emlen, 1974)[3] of the negative correlation between artificial construction coverage and bird species diversity is that, since the urban habitat is fairly novel for bird species, it takes time for them to adapt toward “harmony with the new habitat” and occupy vacant niches in artificial construction. However, the authors refute this opinion by pointing out that the theory is based on the assumption that man-made features, which generate vacant niches, and therefore increase the habitat structural diversity. From the study, the author claim that most of the man-made features do not necessarily increase the diversity of the habitat. To find out the underlying causes of the negative relationship between bird species diversity and artificial construction coverage, the author then studied the bird species that have a higher density under urban settings than under rural settings, implying successful adaptation to the urban environment. From the survey, the house sparrow, rock dove, and American robin were found to be the species that dominated the urban environment.
Figure 1. Gang of four. From left to right, House sparrow (Passer domesticus), common starling (sturnus vulgaris), American robin (Turdus migratorius), and rock dove (Columba livia). Pictures credited to wikipedia.org
The authors found the success of the four bird species within the urban environment is related to the availability of food resources. The main food resource of the urban area is the food provided by people. The authors discovered a strong positive correlation between food provided by humans and the density of the four bird species. Because the quantity of food provided by humans exceeds the caloric requirement of the bird species, the availability of energy essentially become an unlimited factor.
The study brings many insights about the distribution of bird species under urban settings and also offers implications about bird preservation in the urban environment. In contrast, our ecology projects will focus on the diversity and richness of bird species under suburban settings. In our study, we will examine the bird habitats on the northern part of the Grinnell College campus. Grinnell College, located in the middle of Iowa and distant from the major cities, not only offers us an isolated environment to examine the human impact on bird species, but also a chance to verify Lancaster and Rees’ hypothesis on urban adaption of certain bird species. Since the Grinnell College campus is surrounded by “natural” environment, it is easier for bird to retreat from the area with intensive human interference (the area we observed) to the area with less human interference. Therefore, we can observe how human activity influence the habitat choice of bird. Also, we are interested in whether there exists any birds that take advantage of connected habitat, which differs from urban environment that Lancaster and Rees studied. For example, if there exist bird species that choose to forage in area with more human activity, which means more food, and then returns to remote area to rest without human interference.
In today’s
modern and rapidly globalizing world, society is quickly seeing the decline in
natural habitat and the expansion of urban regions. Prairies are giving way to
pavement and population centers, and forests are giving way to far expanses of
concrete jungle. As the green in the world turns into grey, much of the world’s
habitat is being replaced with expansive and towering cities. These new regions
of sprawl are providing a new kind of habitat – one that is frequently seen as
not forgiving for species of plants and animals that rely on them. One organism
affected by this spread is countless bird species across the world. In an
effort to research conservation methods as the unstoppable spread of
urbanization conquers their natural world, ecologists look to comparable
habitats to provide study points for these concrete jungles. One such habitat
is that of islands – regions of natural habitat often isolated in nature
(Fernandez-Juricic and Jokimaki 2001). By using methods carried out in analysis
of island habitat in similar literature, scientists can extrapolate analyses
onto the isolated environments presented in the sparse environment, whether
presented through parks or pathways, that urban environments provide. The
authors aimed to extrapolate conclusions from habitat island theories to
environments provided in urban landscapes in order to further the framework for
urban bird conservation, education, and management (Fernandez-Juricic and
Jokimaki 2001).
The
authors were able to draw several conclusions based on this cross analysis of
sources. One primary driver for bird species richness within urban settings is
the area that urban parks provide (Fernandez-Juricic and Jokimaki 2001). This
is important to understand, as the isolated patches of urban parks, similar to
that of island biomes, are often far and few between within cities and urban
sprawls, meaning that each appearance of it would be especially important for
bird species as they adjust to changing environments around them. A second important
driver in species diversity is both the age and complexity of urban parks
(Fernandez-Juricic and Jokimaki 2001). While somewhat connected, as the age of
a park typically allows for greater diversity in vegetation and age of growth,
the complexity of a park provides greater diversity of habitat for bird
species, something that can be concentrated down in often limited spaces
provided in urban areas for parklands. A third conclusion drawn is that bird
species richness is negatively correlated with the amount of paved ground
within parks (Fernandez-Juricic and Jokimaki 2001). This highlights the
important dichotomy between two park types – those that are more natural and
greener so to speak, and those that are paved open areas with a lower density
of trees. This conclusion shows that birds in urban areas will prefer areas
with less pavement and more green area (figure 1, taken from Fernandez-Juricic
and Jokimaki 2001).
This research is helpful to my groups ongoing project
on Grinnell College’s campus. We are examining the suitability of prairie
habitat patches on the northern reaches of Grinnell College’s land by the
soccer fields for birds. By understanding the ways that island habitats
interact with birds outlined in the literature, the isolated island-like
patches of prairie habitat planted on campus can be assessed comparatively for
their ability to provide harbor for bird species. Having these types of
habitats on our campus is important, as the city of Grinnell is an urbanizing
area compared to generations ago, in that over the years there has been notable
habitat loss both on campus and in the town. Through the reintroduction of properly
planted and managed habitat, the campus can be a natural habitat substitute for
the habitat that has been taken from birds. This is both beneficial for native
sedentary birds and migratory birds alike, hopefully assisting in the bird’s
recovery against rapidly declining numbers (Rosenburg et al. 2019). It would be
appropriate to hypothesize that the lack of paved ground in the soccer field
prairie habitats at Grinnell College would be beneficial in encouraging more
birds to visit the habitats. Furthermore, prairie habitats on campus that are more
diverse in vegetation and possibly containing older growth are more likely to
be better habitat for birds.
References
Fernandez-Juricic, Esteban, and Jukka Jokimäki. "A
habitat island approach to conserving birds in urban landscapes: case studies
from southern and northern Europe." Biodiversity & Conservation 10.12
(2001): 2023-2043.
Rosenberg, Kenneth V., et al. "Decline of the North
American avifauna." Science 366.6461 (2019): 120-124.
