Ecosystems in Our Surroundings
In Xochimilco, boatmen steer their boats through canals and chinampas (artificial farming islands) where axolotls, ahuejote trees, and herons live. A few hundred kilometers away, in a pine-oak forest in the Sierra Madre, there are deer and squirrels. And in Quintana Roo, a reef is full of fish and corals. These are three very different places, but all three are ecosystems. Classifying them helps us understand what conditions the living things that inhabit them share.
Terrestrial and aquatic ecosystems
If you walk through a forest, the trees and deer rely on the ground. If you dive into the sea, the fish and marine plants float or move within the water. What changes in each environment? The way of supporting themselves, breathing, and moving around.
In the diagram, the three final boxes are numbered: 1 terrestrial, 2 marine aquatic, and 3 freshwater aquatic. This way you can say which box each ecosystem belongs in.
Look at the ecosystem classification diagram. State in which box (1, 2, or 3) you would place each of these ecosystems: a holm oak wood, a coral reef, a mountain lagoon,…
Look at the ecosystem classification diagram. State in which box (1, 2, or 3) you would place each of these ecosystems: a holm oak wood, a coral reef, a mountain lagoon, a dehesa (wooded pastureland), a posidonia meadow, and a river.
Characteristic ecosystems of Mexico
Mexico is a megadiverse country: it has almost all the types of ecosystems on the planet. Each one depends on climate, terrain, and available water.
Name two terrestrial ecosystems characteristic of mainland Mexico and one specific to the Baja California Peninsula or the Yucatán Peninsula, mentioning a typical…
Name two terrestrial ecosystems characteristic of mainland Mexico and one specific to the Baja California Peninsula or the Yucatán Peninsula, mentioning a typical species from each.
Describe the ecosystem closest to your local area: state whether it is terrestrial or aquatic, name three living things that inhabit it, and mention an important abiotic…
Describe the ecosystem closest to your local area: state whether it is terrestrial or aquatic, name three living things that inhabit it, and mention an important abiotic factor in it.
On the island of Cozumel, there are species, such as the pygmy raccoon, that live nowhere else in the world (endemic species). Explain the role island isolation plays in…
On the island of Cozumel, there are species, such as the pygmy raccoon, that live nowhere else in the world (endemic species). Explain the role island isolation plays in the occurrence of endemic species.
Marine and freshwater aquatic ecosystems
Light and water quality limit seagrasses
Seagrasses are plants: they carry out photosynthesis and need light. That is why they grow only in shallow, clear waters, where light reaches the bottom. If the water becomes cloudy (turbidity) because of construction, dredging, or runoff, less light gets in and the leaves photosynthesize less, produce less food, and weaken. If fine sediments also settle on the bottom and the leaves, they cover them, block even more light, and bury the stems and roots. It is enough for the damage to happen nearby: no plant has to be pulled up.
When a meadow degrades, the fish, crustaceans, and turtles that depend on it also lose shelter and food, and local fishing in the area declines.
Point out two differences between a freshwater ecosystem and a marine ecosystem and explain why most fish cannot move from one environment to the other.
Point out two differences between a freshwater ecosystem and a marine ecosystem and explain why most fish cannot move from one environment to the other.
During the expansion of a marina over a Posidonia oceanica meadow, the construction work drastically increases water turbidity and deposits fine sediments onto the…
During the expansion of a marina over a Posidonia oceanica meadow, the construction work drastically increases water turbidity and deposits fine sediments onto the seabed. The project developer claims: 'The meadow will not suffer any damage because the breakwater is being built 50 meters away and we are not directly uprooting any plants.' Refute this claim by explaining the physiological effects that turbidity and sedimentation cause on these marine plants. Furthermore, predict two cascading ecological consequences on the coastal ecosystem and local fisheries.
An amateur environmental group proposes restocking a river estuary by introducing brown trout specimens caught in the upper course of that same river, arguing that…
An amateur environmental group proposes restocking a river estuary by introducing brown trout specimens caught in the upper course of that same river, arguing that 'since it is the same river basin, the species will acclimate without any issues.' Refute the ecological and physiological viability of this proposal by analysing how three abiotic factors vary (current velocity, temperature and dissolved oxygen concentration, and salinity) between both sections. Justify why the adaptations of these resident trout, moved without prior acclimation, would make their survival in the river mouth very unlikely.
Ecosystems transformed by humans
A dehesa is a holm oak or cork oak wood cleared by humans to be used as pasture and farmland. Explain why it is considered a human-modified ecosystem while also being an…
A dehesa is a holm oak or cork oak wood cleared by humans to be used as pasture and farmland. Explain why it is considered a human-modified ecosystem while also being an example of sustainable land use with high biodiversity.
Matter and energy in ecosystems
Whether it is a jungle, a reef, or a milpa, all ecosystems work by the same rule: matter is recycled and energy flows in one direction only.
The carbon cycle
Carbon enters living things as $\text{CO}_2$ from the atmosphere, thanks to the photosynthesis of plants, algae, and seagrasses. It passes from one organism to another through feeding. It returns to the atmosphere through the respiration of all living things, through decomposition (fungi and bacteria), and through combustion (fires, burning of firewood and fossil fuels).
The nitrogen cycle
Nitrogen is very abundant in the air ($\text{N}_2$), but plants cannot use it in that form. Certain bacteria, like the ones that live in bean roots, fix it and convert it into forms the plant can absorb. Animals obtain it by eating plants or other animals. When organisms die, decomposers return it to the soil, other bacteria transform it (nitrification), and some return it to the air (denitrification).
Why trophic pyramids are pyramids
At each trophic level, most of the energy is lost: a simple rule says that only about 10% passes to the next level. That is why there are many producers, fewer herbivores, and very few large carnivores, and food chains are short.
You want to compare the biodiversity of a plantation pine forest with that of a nearby holm oak wood. Design a simple study: state what you would observe or count, how…
You want to compare the biodiversity of a plantation pine forest with that of a nearby holm oak wood. Design a simple study: state what you would observe or count, how you would make the measurements comparable, and what result you would expect to get.
Back to the beginning: Xochimilco (fresh water, with transformed chinampas), the pine-oak forest (terrestrial), and the reef (marine) are different ecosystems because the physical environment and its abiotic factors change; in all three, matter is recycled and the Sun's energy flows in one direction only.