Investigation question: Field notes from four ecosystems that share no species describe sixteen pairs of organisms but never name the relationship. Can your group decode who gains and who loses from the evidence, find the pattern the four ecosystems share, and predict the four missing interactions before they are revealed?
Case-file cards (teacher prints and cuts apart; 16 cards)
1 K1 · Kelp forest · Señorita and blacksmithThe señorita is a slim, cigar-shaped fish. Blacksmith are dark, plankton-eating fish that hover in groups and sometimes hold still, head tipped down, beside a señorita. Señoritas: at midday, señoritas on reefs crowded with blacksmith had 30 food items in their stomachs, several of them tiny parasites picked off other fish; señoritas on reefs with few blacksmith had 21. Blacksmith: fish near señoritas carried 1 skin parasite each, on average; blacksmith on a reef with no señoritas carried 7.
2 K2 · Kelp forest · Giant kelp and young rockfishEach spring, young rockfish of several kinds drift in from the open ocean and settle into kelp forests. They eat tiny drifting animals, not kelp. Giant kelp: stalk tips with many young rockfish around them grew 21 cm per day; stalk tips with few grew 20 cm per day. Young rockfish: divers counted 26 per 100 meters of swim path under the kelp and 3 per 100 meters over bare sand nearby at the same depth, where diving birds and bigger fish could spot them.
3 K3 · Kelp forest · Purple sea urchin and sea otterDivers surveyed 12 rocky reefs where sea otters feed and 12 similar reefs with no otters. Purple sea urchins: 3 per square meter on otter reefs; 40 per square meter on reefs without otters. The urchins left on otter reefs hid deep in cracks in the rock. Sea otters: watchers on shore timed otter dives. On reefs where urchins were still common, an otter came up with food on 8 of every 10 dives; on reefs where urchins were scarce, on 5 of every 10.
4 K4 · Kelp forest · Woody-stemmed kelp and giant kelpWoody-stemmed kelp is a short kelp, about as tall as a person, that grows beneath giant kelp, which reaches the surface. Both need sunlight on the seafloor to grow and to start new young plants. Divers cleared one kind from test plots and checked a year later. Woody-stemmed kelp: it covered 60 percent of the seafloor where giant kelp had been cleared and 15 percent under untouched giant kelp. Giant kelp: 9 young plants per square meter took hold where woody-stemmed kelp had been cleared; 2 per square meter where it was left.
5 D1 · Mojave Desert · Merriam's kangaroo rat and harvester antsKangaroo rats and harvester ants both gather the seeds of the same desert wildflowers and grasses. Biologists fenced kangaroo rats out of some plots, removed ant colonies from others, left some plots alone, and counted three years later. Kangaroo rats: 14 per plot where the ants had been removed; 11 per plot where ants were left. Harvester ants: 31 colonies per plot where kangaroo rats were fenced out; 20 colonies per plot where rats were present.
6 D2 · Mojave Desert · Catclaw acacia and desert mistletoeDesert mistletoe is a leafless plant with green, jointed stems that grows in clumps on the branches of desert shrubs and trees. It makes some of its own food from sunlight, but its root-like strands grow into the branch wood and take water and minerals. Catclaw acacia: after a dry year, heavily infested shrubs made 35 seed pods each; shrubs with no mistletoe made 90. Desert mistletoe: clumps were found only on living branches, and clumps on branches that died also died within a year.
7 D3 · Mojave Desert · Joshua tree and yucca mothA female yucca moth gathers pollen from Joshua tree flowers, flies to another tree, lays her eggs inside a flower and presses pollen onto it. Her larvae eat some of the developing seeds. Joshua trees: of 100 flowers that moths could reach, 28 became seed pods; of 100 flowers wrapped in fine mesh to keep moths out, 0 did. Pods with larvae inside still held most of their seeds. Yucca moths: the larvae eat nothing but developing Joshua tree seeds, and no larvae of this moth were found on any other plant at the site.
8 D4 · Mojave Desert · Desert dandelion and desert tortoiseDesert dandelion is a yellow spring wildflower. Biologists fenced some plots so tortoises could not get in and compared them with open plots. Desert dandelion: plants inside the fences made 40 seeds each; plants in open plots, where tortoises bit off flowers and leaves, made 22. Few plants were killed outright. Desert tortoises: tortoises whose home areas had thick patches of spring wildflowers gained 120 g over the spring; tortoises where wildflowers were sparse gained 30 g.
9 C1 · City park · Lichen and coast live oakLichens are crusty, gray-green patches on bark and stone. Each one is a fungus living with an alga or a cyanobacterium that makes food from sunlight. Lichens do not grow into wood or take sap. Lichen: patches on oak bark grew 4 mm wider per year; patches on the park's concrete benches grew 1 mm per year. Coast live oaks: trunks heavily covered in lichen added 2.0 mm of new wood per year; trunks with almost no lichen added 2.1 mm.
10 C2 · City park · Cooper's hawk and rock pigeonCooper's hawks are crow-sized hawks that now nest in many California city parks. Cooper's hawks: about 4 of every 10 prey brought to a nest were pigeons or doves. Hawk pairs in parks with many pigeons raised 4 chicks a year; pairs in parks with few pigeons raised 2. Rock pigeons: in a park where a pair of Cooper's hawks nested, the pigeon flock fell from 220 to 150 birds over two years; in a similar park with no hawks, it went from 210 to 205.
11 C3 · City park · Rock pigeon and feather louseFeather lice are flat, wingless insects about 2 mm long. They spend their whole lives on one bird, eating the soft, fluffy parts of its feathers. Rock pigeons: over one cold winter, 80 of every 100 pigeons that had been treated to remove lice survived, compared with 60 of every 100 heavily infested pigeons. Pigeons with chewed feathers lose more body heat. Feather lice: on a living pigeon, lice lived for weeks and laid eggs on the feathers; lice that fell off a bird died within a few days.
12 C4 · City park · Western bluebird and European starlingBoth birds nest in holes, such as old woodpecker holes in park trees, and a park has a limited number of them. Starlings often chase bluebirds away from a hole, but the fights cost them time and sometimes the hole. Western bluebirds: where starlings were common, 20 of every 100 bluebird pairs found a nest hole; where starlings were rare, 55 of every 100 did. European starlings: where bluebirds were common, 72 of every 100 starling pairs found a nest hole; where bluebirds were rare, 86 of every 100 did.
13 R1 · Rainforest · Mantled howler monkey and howler botflyA botfly larva lives under the skin of a howler monkey, often on the neck, growing inside a small swelling for several weeks before it drops to the ground and becomes an adult fly. Howler monkeys: in a year with many botflies, 30 of every 100 young monkeys died; in a year with few botflies, 12 of every 100 died. Most adult monkeys carried a few larvae and survived. Howler botflies: larvae of this kind of botfly have been found growing only in howler monkeys.
14 R2 · Rainforest · Canopy tree and orchidsMany rainforest orchids live perched high on tree branches. Their roots grip the bark and soak up rain; they make their own food from sunlight and take nothing out of the tree. Canopy trees: trees carrying many orchids added 12.0 mm to their trunk width in a year; trees carrying few added 12.5 mm. Orchids: of 100 young orchids tied onto branches 25 m up, 78 were alive a year later; of 100 planted on the dim forest floor, 9 were.
15 R3 · Rainforest · Leafcutter ants and their fungusLeafcutter ants carry leaf pieces into their underground nest, chew them into mush and spread it on a spongy fungus garden. The ants and their young eat swollen tips that the fungus grows. A young queen carries a pellet of fungus with her to start each new nest. Leafcutter ants: of 10 lab colonies whose garden was taken away, none survived a month, even with fresh leaves; all 10 colonies that kept their gardens survived. Fungus: gardens kept without ants were overgrown by molds within a week, and this fungus has never been found growing wild away from leafcutter nests.
16 R4 · Rainforest · Jaguar and collared peccaryCollared peccaries are pig-like animals that travel in small herds. Jaguars: about one third of the prey remains in jaguar droppings were peccaries. Female jaguars in areas with many peccaries raised a litter about every 2 years; where peccaries were scarce, about every 3 years. Collared peccaries: in forest where jaguars hunt, 45 of every 100 young peccaries lived to their first birthday; in a nearby forest where jaguars had been hunted out, 70 of every 100 did.