Changes in weather conditions and food availability are not the only changing features of ecosystems. In fact, an entire ecosystem can change during a process called ecosystem succession. Scientists have studied how the diversity of soil animals changes during ecosystem succession, focusing on a group of soil mites called oribatids. Oribatids are tiny, abundant, and diverse, which means that you can find an entire community of them in a small sample of soil.
There are also many resources available to help identify various oribatid species, so they are a perfect organism to observe to study changes in soil ecosystem diversity. Also, the mobility of oribatids is relatively limited, since they exist in the deep soil are restricted to moving through soil pores and can occasionally move by passive dispersal.
Therefore, oribatid communities mainly develop through the process of ecosystem succession. In a recent study, scientists carried out in a chronosequence of forests that are re-growing after cropland abandonment.
They wanted to know if similar forests of different ages have the same soil communities. Scientists hypothesized that croplands probably had only a few oribatid species in low abundances, but that complex communities with high diversity would develop in older forests.
Comparing current aerial photographs with others from the s, scientists determined which areas had been forests in the s long-established forests , and which had been croplands recent forests. Among the recent forests, we also distinguished between isolated forests surrounded mainly by croplands and most likely showing oribatid communities similar to those found in croplands and those connected to other forests probably with oribatid communities similar to those found in old forests.
Scientists observed two important results. First, long-established and recent but connected forests showed similar numbers of oribatids and similar numbers of species, which were higher than what was seen in the isolated forests. Second, oribatid communities in isolated and connected recent forests shared more species than they did with long-established forests Figure 3 , bottom.
Likely, oribatids arrive mainly by passive dispersal early in ecosystem development. That is probably why recent forests connected to long-established forests quickly establish oribatid communities similar to those in the long-established forests.
But as the recent forest ecosystem continues to develop, lack of refuge availability and access to food may prevent some oribatid species from permanently settling there. This could explain why oribatid communities in recent and connected forests are more like those of isolated forests and thus to those of croplands Figure 3. Scientists studied ecosystem aging in Canadian boreal forests [ 4 ].
The almost instantaneous outbreak of SARS in different parts of the world is an example of such potential, although rapid and effective action contained its spread. Warming of the African Great Lakes due to climate change may create conditions that increase the risk of cholera transmission in surrounding countries C An event similar to the Spanish flu pandemic, which is thought to have killed 20—40 million people worldwide, could now result in over million deaths within a single year.
Such a catastrophic event, the possibility of which is being seriously considered by the epidemiological community , would probably lead to severe economic disruption and possibly even rapid collapse in a world economy dependent on fast global exchange of goods and services. Algal blooms and fish kills S While small increases in nutrient loading often cause little change in many ecosystems , once a threshold of nutrient loading is achieved, the changes can be abrupt and extensive, creating harmful algal blooms including blooms of toxic species and often leading to the domination of the ecosystem by one or a few species.
Severe nutrient overloading can lead to the formation of oxygen-depleted zones, killing all animal life. Fisheries collapses C18 : Fish population collapses have been commonly encountered in both freshwater and marine fisheries. Fish populations are generally able to withstand some level of catch with a relatively small impact on their overall population size. As the catch increases, however, a threshold is reached after which too few adults remain to produce enough offspring to support that level of harvest, and the population may drop abruptly to a much smaller size.
For example, the Atlantic cod stocks of the east coast of Newfoundland collapsed in , forcing the closure of the fishery after hundreds of years of exploitation, as shown in Figure 3. Most important, the stocks may take years to recover or not recover at all, even if harvesting is significantly reduced or eliminated entirely.
Species introductions and losses : Introductions or removal of species can cause nonlinear changes in ecosystems and their services. For example, the introduction of the zebra mussel into U. The loss of the sea otters from many coastal ecosystems on the Pacific Coast of North America due to hunting led to the booming populations of sea urchins a prey species for otters which in turn led to the loss of kelp forests which are eaten by urchins.
Changes in dominant species in coral ecosystems : Some coral reef ecosystems have undergone sudden shifts from coral-dominated to algae-dominated reefs. The trigger for such phase shifts, which are essentially irreversible, is usually multifaceted and includes increased nutrient input leading to eutrophic conditions, and removal of herbivorous fishes that maintain the balance between corals and algae. Once a threshold is reached, the change in the ecosystem takes place within months and the resulting ecosystem, although stable, is less productive and less diverse.
One well-studied example is the sudden switch in from coral to algal domination of Jamaican reef systems. This followed several centuries of overfishing of herbivores, which left the control of algal cover almost entirely dependent on a single species of sea urchin , whose populations collapsed when exposed to a species-specific pathogen.
Regional climate change C In the Sahel region of North Africa, vegetation cover is almost completely controlled by rainfall. When vegetation is present, rainfall is quickly recycled, generally increasing precipitation and, in turn, leading to a denser vegetation canopy. Model results suggest that land degradation leads to a substantial reduction in water recycling and may have contributed to the observed trend in rainfall reduction in the region over the last 30 years. This summary is free and ad-free, as is all of our content.
You can help us remain free and independant as well as to develop new ways to communicate science by becoming a Patron! Home » Ecosystem Change » Level 2 » Question 7. Previous Question. Next Question. How do ecosystems change over time? This question addresses: Time scales of change: how long it takes for the effects of change in an ecosystem to become apparent also referred to as lag time. Inertia : the delay or slowness in the response of an ecosystem to certain factors of change.
Figure 7. Emergence of infectious diseases: An epidemic spreads if a certain transmission threshold is crossed, that is if, on average, each infected person infects at least one other person. The epidemic dies out if the infection rate is lower. When humans live closely together and in contact with infected animals, epidemics can potentially spread quickly through the well connected and mobile world population.
The almost instantaneous outbreak of SARS in different parts of the world is an example of such potential, although rapid and effective action contained its spread. Algal blooms and fish kills: Excessive nutrient loading causes eutrophication of freshwater and coastal ecosystems. While small increases in nutrient loading often cause little change in ecosystems, once a threshold is reached the changes can be abrupt and extensive, causing bursts of algae growth.
Severe eutrophication can kill animal life in the water by causing oxygen-depleted zones. Naturally occurring geological hazards that affect ecosystems include volcanoes, earthquakes and tsunamis. Biological factors — disease, invasive species, algae blooms — also contribute to changes in ecosystems. Harris holds a Bachelor of Science in Mathematics from Penn State University; she taught high school math for several years and has also worked in the field of instructional design.
How Humans Disrupt the Ecosystem. Five Types of Ecological Relationships. Depletion of the Ecosystem. The Effects of Animal Overpopulation. Three Examples of Environmental Disturbances in Biomes.
How to Maintain Biodiversity in the Forest's Ecosystems. The Three Types of Environmental Adaptations. The Effects of Typhoons.
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