e_moon60 (e_moon60) wrote,

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A Little Bit on Ecology

Though it's artificial, a water garden can be a way to study local interactions of aquatic life and terrestrial life.  Our water garden, now over ten years old (upper part) and ten years old (lily pond) is rain-fed (with collected rainwater) and has successful reproducing populations of native insects, amphibians, and questionably reproducing populations of reptiles (does the red-lined ribbon snake reproduce here?  We don't know.  I'm pretty sure the turtle that shows up occasionally doesn't.)   Though I haven't done formal experiments ( sigh)  I have done a lot of observation and photography...and it fits in well with research done by others on the influence of aquatic and terrestrial environments on each other.

Every living thing in the yard and the water garden (note: in the yard and water garden--don't come to me with exceptions from deep-ocean "hot smoker" vents, etc., OK?)  has some basic needs:  something to eat, something to breathe, somewhere to be that provides the substrate (habitat) suitable for that plant or critter.  The green plants all need sunlight to photosynthesize and some carbon dioxide as a carbon source.  They also need specific minerals...and a substrate that supports their structure, whether it's deep soil for some of the trees, or water of specific depth for the aquatic plants.  The critters all need oxygen--from the oxygen in the water, if they're fully aquatic, or from the air, if they breathe air...and they need an energy source (carbon compounds they can "burn" in oxygen) and specific minerals. 

Nutrients cycle through from one to another...most obviously in predation, when the giant water bug nails a tadpole, or the tadpole nails an insect larva, or the bird nabs a grasshopper....slightly less obviously when birds that perch in the trees before coming down to water poop onto the soil and provide nitrogen for the tree...or a squirrel electrocutes itself on the powerline and falls to the group to be dismembered by the decomposers, who also leave nutrients in the soil for the plants.   When I was in school, we were taught the "pyramid" version of who eats what, with the herbivores eating plants, and the carnivores eating herbivores, and bigger predators eating smaller ones.   Well....not exactly.  In fact, not even close.

The water garden has four distinct zones.  Zone 1, the upper end is mostly shaded in summer, and has a "stream" configuration.   Its water source is water pumped from the bottom of the lily pond downstream and entered a shallow pool lined with small rocks (a favorite watering place for small birds.)  Water then falls over a small (maybe 4 inch) drop into a larger, deeper pool with an irregular bottom, and rocks on one side that offer an overhang (and thus, perpetual shade).  There's a rock dam at the foot, with a drop of perhaps 8 inches into a deep narrow pool, with outflow in a kind of groove into Zone 2.  The drops and the water velocity are enough to keep the water well-oxygenated.   Because of the overhanging trees, Zone 1 gets a lot of terrestrial nutrient input in the form of leaves (in the fall) and ash seeds (early summer),  from birds that perch in the trees and poop directly into the stream, and from birds bathing in the stream (and pooping in it then), from insects falling from the trees into the water.  When other terrestrial animals leave their deposits within a few feet of the stream, after drinking there, the next hard rain washes them into the stream.   Meanwhile, Zone 1 aquatic life provide nutrients to terrestrial life.  Spiders spin webs near the stream to capture insects--either coming to drink, like wasps and bees and flies and gnats, or those that are aquatic larvae but terrestrial in adult life: dragonflies, damselflies, mosquitoes, etc.   Birds feed on insects (especially at some times of the year), including those that spend their pre-adult life in the water.  Aquatic tadpoles feeding on algae and aquatic insects (when not eaten themselves by the larger ones or by the snake in the water) turn into air-breathing frogs and toads that eat insects...and are prey for snakes, some birds (herons, especially) and the mammals (raccoons, especially) that come to drink and hunt.

Zones 2, 3, and 4 add new habitat types.  Round Pool, Zone 2, is a pool that receives considerable sun in summer and has a strong current running across it; it has some emergent vegetation on the planting shelf along one side, and overhanging understory vegetation on the other--with one side completely open.  It has an even depth across the middle.  Zone 3 is a narrow, exposed, channel between Round Pool and the Lily Pond; water velocity is fairly high and it is a favorite watering place for larger flocking birds, like White-winged Dove (year 'round) and Cedar Waxwing (seasonally.)    Zone 4 is the Lily Pond, the deepest and largest of the pools, with a large bed of water iris at the upstream end and water lilies at the downstream.  It is partly shaded by a young oak, but receives a lot of sun.  Both in Zone 2 and Zone 4, the biggest orb weavers, Argiope aurantia, build webs; the smaller webs of the long-jawed orb-weavers are found in 1, 2, and 4.  The Lily Pond's abundance of surface cover in the form of lily pads provides ideal habitat for the big fishing spider; by midsummer, this spider may successfully predate on large dragonflies.   I was able to photograph such an attack this summer for the first time.

In order to build a proper food web for this little system, I'd need to do more sustained study than I've had time for (there's this having books to write, for one thing...)   I have lists of what I've observed there, the species I've been able to identify...but I've seen aquatic larvae that I know nothing about.  I've IDed only four of the spiders observed there.  I'm still finding beetles and bugs that I don't know (or didn't know were there.)   There are at least three species of algae, and by looking at tangles of it under a dissecting microscope, I've found even more things I don't know (the hydra and the tardigrades I recognized...some of the other stuff...mystery.)   And I haven't touched the bacterial components yet.   I do know (from game-cam captures) what native wild mammals show up at night (raccoons, opossums, a gray fox, deer) though I'm also sure that even smaller ones (mice, etc.) come to drink (certainly squirrels do, by day.)  So do non-natives, like cats. 

In a natural system, a stream would also water the plants along its banks, including trees.  This water garden, being lined, isn't the water source for the trees, so it's partly isolated from normal cycle of nutrients, but not entirely.  Some water-garden owners worry about leaves falling into their streams and ponds, and discoloration and so on--they want super-clean water gardens.  I wanted (and have) something I think is more interesting.   And if I ever have the time to do more than look and take pictures...well, I have no excuse for being bored, that's for sure.

Tags: ecology, food webs, water garden

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