A Little Bit More
The word “vernal”, which refers to spring, is not a common term in our everyday language. Probably the time it is most often used is when we use it during the Vernal Equinox (springtime point when day and night are the same length). In the fall, this same phenomenon is called the Autumnal Equinox (again, day and night are the same length).
Vernal pools are much more common than people realize. Since they’re often small, shallow, and most dry up in summer, many landowners never realize how important they are for a wide assortment of different organisms. Not all vernal pools dry up each year; in wet years a pool may not dry up but in dry years, it may be bone dry well before summer arrives. But the most important quality of these pools is the fact that there are no fish living there; fish can’t survive in these on-again, off-again bodies of water. Without fish, a major predator is eliminated, and life is not quite so dangerous.
As the poster notes, organisms’ lifecycles are accelerated in vernal pools; they must either reproduce or develop to a point where they can leave. For many of the invertebrates, like the Fairy Shrimp, eggs hatch, young grow quickly to adult stage and then they reproduce before the pond dries up. The eggs left behind in a dry pond will lie dormant until next year’s rains revive them and the process begins again. But for vertebrates, like the Spotted Salamander, these animals lay their eggs early in spring, and the young grow and change into land-dwelling salamanders quickly, often before the pond dries. Of course, in unusually dry years when these ponds dry up sooner than normal, many of these organisms perish before they’re old enough to leave or reproduce. Vernal ponds are definitely an iffy proposition, but in years when they’re filled long enough, enough young survive to offset the bad years.
Activities
Science – All Seasons
Objectives: Understand reason for seasonal change
Materials: none
Vernal Equinox – day and nights same length
Summer Solstice – day length longest of year
Autumnal Equinox – day and nights same length
Winter Solstice – day length shortest of year
Since vernal refers to spring and this implies season, I think it would be helpful to share with students why we have seasons in the first place. Although this is a central phenomenon to life on earth, many people are not entirely familiar with HOW the seasonal changes are accomplished. Many people, this includes many adults, believe that the earth is closer to the sun in summer but this exercise will show that it’s the angle in relation to the sun that actually causes our seasons, not distance.
The concept of seasons is a bit difficult for people to quickly grasp so I’ve come up with a way to demonstrate this that has worked well for me. Although this exercise can be demonstrated with a globe, I’ve found it helpful to use a person as our “Earth” model to demonstrate initially. Once you’ve worked through this exercise using a person, a globe can be substituted to cement the concept. Be sure to look at the diagram for student/earth rotation that we’ve included to clarify step #4.
1. Establish a central, cleared location in the room that is to be an imaginary “campfire” (use any prop you wish to represent the fire)
2. Select one student who is willing to help with the demonstration
3. Instruct the student to directly face the campfire. Tell your student/earth that they’re cold and should lean toward the fire to warm their head and hands (the earth tilts 21° in relation to its orbit around the sun). This position will represent the Summer Solstice
4. Now have the student/earth maintain the same tilt forward, revolve around the heat source just a quarter of the circle – either direction, but he/she must remain facing the SAME direction –not the campfire - during the entire revolution. (In other words, if the student begins by facing the front of the room when facing the fire, for example, they must face the front the entire time they revolve around the campfire.) After a quarter turn, their shoulder should now be closest to the camp fire. This represents the Autumnal Equinox - see the diagram
5. Now tell the student/earth to continue in the same direction a quarter turn again keeping his/her body in the same plane (angle) as before (facing the same direction beyond the campfire). At this point their back side should be facing the fire. They should still be gently tilted forward which means that their bottom, not their head, is closest to the fire and is being warmed. This represents the Winter Solstice
6. Now have the student/earth continue revolving around the fire for the third quarter of the circle, maintaining their same orientation . Once again their shoulder (it will be the opposite one now) will be closest to the fire. They should still be leaning forward. This represents the Spring Equinox
7. And lastly, have them resume revolving for the last quarter of the circle. At this point they should be back to the beginning facing the fire (this would have taken 365 days to accomplish) This represents the Summer Solstice once again.
8. Of course, we’ve assigned the northern hemisphere to be the head of our students while their bottom is the southern hemisphere but it works either way.
9. If you want to repeat this procedure with a globe, start with the northern hemisphere at the Summer Solstice so the procedure mimics what they’ve just seen with the student.
10. To add an added bit of realism to this procedure, you might want also to spin the earth as it moves around the sun.
I think you’ll find that this simple graphic example will greatly help students understand just how our seasons are affected.
Key Concepts
Predator/Prey Relationships, Populations and Ecosystems, Life Cycles, Growth and Development, Food Webs /Food Pyramids, Environmental Issues, Adaptations and Diversity
Questions
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