Chapter 1

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Biological Sciences
Marc Cadotte

C HAPTER 1: T HE W EB OF L IFE DEFORMITY AND DECLINE IN AMPHIBIAN POPULATIONS: A CASE STUDY  Scientists were especially worried about amphibians for 3 reasons 1. The decline appeared to have started recently across wide regions of the world 2. Some of the populations in decline were located in protected or pristine regions, seemingly far from the effects of human activities 3. Many scientists view amphibians as good biological indicators of environmental conditions a. Amphibians have permeable skin (through which pollutants and other molecules can pass) b. Most amphibians spend part of their lives in water and part on land – exposed to a wide range of potential threats including water and air pollution INTRODUCTION  Humans have an enormous impact the planet  We don’t just have an effect the global environment we are part of it  Natural systems are driven by the ways in which organisms interact with one another and with their physical environment  Thus to understand how natural systems work, we must understand ecology  Ecology: the scientific study of how organisms affect – and are affected by – other organisms and their environment Concept 1.1 Events in the natural world are interconnected CONNECTION IN NATURE  Connection in nature – use that phrase to refer to the fact that events in the natural world can be linked or connected to one another - Connections occur as organisms interact with one another and with their physical environment - Does not necessarily mean that there is a strong connection among all organisms - Even species that do not interact directly with each other can be connected by shared features of their environment » Early Observations Suggest that Parasites Cause Amphibian Deformities  Sessions found that the deformed amphibians all contained a parasite known to be Ribeiroia ondatrae (tremadote flatworm)  Ruth hypothesized that these flatworms caused the deformities - Implanted glass beads that mimic the effects of the parasite - Reported that the beads caused deformities similar to those found by Ruth » A Laboratory Experiment Tests the Role of Parasites  When Ruth found deformed amphibians he assumed that they were isolated, local phenomenon  One source of concern was that the deformities might be caused by pollutants, such as pesticides, polychlorinated biphenyls (BCPs), or heavy metals - However none of these substances were found in the water from the 2 ponds - Johnson turned his attention to other factors that might cause deformities - Performed a controlled experiment - Controlled experiment: in which an experimental group was compared with a control group - Took eggs from a region not known to have deformities and placed tadpoles in 1 L containers each assigned at random to 1 of 4 treatments 1) 0 2) 16 Ribeiroia parasites 3) 32 Ribeiroia parasites 4) 48 Ribeiroia parasites - As the number of parasites increased, fewer of the tadpoles survived to metamorphosis, and more of the survivors had deformities - Since exposure to the parasite killed up to 60% of the tadpoles, the results also suggested that the parasites could contribute to amphibian decline  The life cycle of Ribeiroia. The life cycle of Ribeiroia utilizes three different kinds of hosts: snails, larval amphibians or fish, and birds and mammals. Many other parasites have similarly complex life cycles. Some parasites, like Ribeiroia, can alter the appearance of behaviour of their second intermediate host, making that host more vulnerable to predation by their » A Field Experiment Suggests that Multiple Factors Influence Frog Deformities  To examine the possible joint effects of parasites and pesticides, Kiesecker conducted a field experiment in 6 ponds, all of which contained Ribeiroia, but only some of which contained pesticides  3 close to farms (showed detectable levels of pesticides), 3 not so close (did NOT show levels of pesticides)  In each pond, the tadpoles in 3 cages were exposed to the parasites, while the tadpoles in the other 3 cages were not  It was found that tadpoles in cages that protected them from Ribeiroia did not develop deformities  Some tadpoles in cages not protected from the parasite developed deformities; the highest percentage of deformities occurred in tadpoles exposed to both Ribeiroia and pesticides  Kiesecker hypothesized that pesticides might decrease the ability of frogs to resist infection by parasites  One reason for the increased number of parasitic infections appeared to be that the frogs’ immune response was suppressed by the pesticide » Connections in Nature Can Lead to Unanticipated Side Effects  Why has the frequency of amphibian deformities increased? - Kiesecker and Rohr: pesticides may decrease the ability of amphibians to ward off parasitic attack, and hence deformities are more likely in environments that contain pesticides - The first synthetic pesticides were produced in the 1930s, thus the amphibians have increased exposure to pesticides - Other environmental changes may also contribute to the observed increase in amphibian deformities - Ex. Addition of nutrients to natural or artificial pods can lead to increases in parasite infections and amphibian deformities o Nutrients enter pond  growth of algae  snails with Ribeiroia eat algae  life cycle » We Live in an Ecological World  The fact that events in nature are interconnected means that when people alter one aspect of the environment, we can cause other changes that we do not intend or anticipate  Globally, the past few decades have seen an increase in the appearance and spread of new diseases, and that these are the effects of human actions directly or indirectly Concept 1.2 Ecology is the Scientific Study of Interactions Between Organisms and Their Environment  Ecology: the scientific study of interactions between organisms and their environment - The scientific study of interactions that determine the distribution and abundance of organisms - As used by ecologist, refer to a scientific endeavor  Ecology is a branch of biology while the environmental science is an interdisciplinary field that incorporates concepts from the natural sciences and the social sciences  Environmental ecology is focused more specifically on how people affect the environment and how we can address environmental problems » Public and Professional Ideas About Ecology Often Differ  Many members of the public think that: 1) There is a “balance of nature,” in which natural systems are stable and tend to return to an original, preferred state after a disturbance 2) Each species in nature has a distinct role to play in maintaining that balance  Such ideas can have moral or ethical implications on people who hold them  Ecologists now recognize that natural systems do not necessarily return to their original state after a disturbance, and they understand that seemingly random perturbations often play an important role in nature  Connection in nature form the basis for the first of eight ecological maxims “You can never just do one thing” (table 1.1 p.9) » The Scale of an Ecological Study Affects What Can be Learned from it  Ecologists must select the most appropriate dimension or scale  Scale: a dimension for collecting observations, including both time and space  Every ecological study addresses events on some scales but ignores events on other scales » Ecology is Broad in Scope  Ecologists study interactions in nature across many levels of biological organizations  Ecological studies usually emphasize one or more of the following levels: - Individuals - Populations - Communities - Ecosystems - Landscapes - Biosphere  Population: is a group of individuals of a single species that live in a particular area and interact with one another  Community: an association of interacting
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