science-2018:ENV.ER.5
science-2018:ENV.ER.5 Wildlife and wilderness
Learning goal: Describe the goals and tools of wildlife and wilderness management; explain how species become endangered and how recovery is attempted; distinguish introduced from invasive species and assess the benefits and risks of introducing a species; describe the impacts of invasive species on Ohio food webs; and use biodiversity comparisons and biomagnification reasoning to evaluate management decisions.
Wildlife and wilderness as resources. Wildlife is a renewable resource if the harvest and the habitat are managed so that populations persist; a fishery or a deer herd can be used indefinitely or destroyed in a decade. Wilderness is land kept largely free of human alteration, valued for the ecosystems it holds, the species that need large undisturbed areas, the water it filters and the reference it provides for judging altered land. In the United States, the Wilderness Act of 1964 lets Congress designate federal land where roads, vehicles and permanent structures are excluded. Managing wildlife and wilderness means deciding what condition to aim for, measuring the present condition, and changing what people do until the two match.
Wildlife management tools. The first tool is population monitoring: counts, surveys, tagging, harvest records and, increasingly, camera and acoustic sensors. The second is habitat management: protecting, restoring or creating the food, water, cover and space a species needs, which usually does more than anything aimed at the animals themselves. The third is harvest regulation: seasons, bag limits, size limits and licenses set so that removals stay below the population's growth. In Ohio the state wildlife agency sets deer seasons and bag limits each year from survey and harvest data; with the wolves and cougars gone, regulated hunting is the main population control on white-tailed deer, and where deer are too abundant they strip the forest understory, eliminate the seedlings of the next forest and the wildflowers that insects depend on, and collide with vehicles. Management can also mean reintroducing a predator, moving animals between areas, or controlling disease. Every tool has a cost and a constituency, which is why plans are written with stakeholders.
Endangered species. A species is endangered when it is in danger of extinction across all or a significant part of its range, and threatened when it is likely to become endangered soon. The federal Endangered Species Act of 1973 requires listing on the basis of scientific evidence, prohibits take (harming) of listed animals, requires federal agencies to avoid destroying or adversely modifying designated critical habitat through actions they fund or permit, and requires recovery plans; states, including Ohio, keep their own lists. The causes are the same in nearly every case, in rough order of importance: habitat loss and fragmentation; overharvest; invasive species; pollution, including biomagnifying toxins; and now climate change. Recovery attacks the cause. The bald eagle is the standard example: DDT in its fish prey thinned its eggshells until they broke under the incubating parent, the population collapsed, the pesticide was banned in 1972, habitat and nests were protected, and the species was removed from the federal list in 2007. Ohio's nesting eagles went from a handful in the 1970s to hundreds today. The lesson is that the recovery followed identification of the mechanism (biomagnification), not just protection of the birds.
Introduced and invasive species. An introduced (non-native, exotic) species is one that humans have moved, deliberately or accidentally, beyond the range it reached on its own. Most introduced species fail to establish, and many that establish do little harm; wheat, honeybees and ring-necked pheasants are introduced. An invasive species is an introduced species that spreads aggressively and causes ecological or economic harm. The distinction matters because policy targets invasiveness, not foreignness. Invaders succeed because they arrive without the predators, parasites and competitors that held them in check at home, and because disturbed habitats give them openings; repeated introductions, such as new arrivals in ballast water or nursery stock, also raise the chance that one population establishes. Because an established invader is usually expensive or impossible to remove, preventing introductions is generally cheaper than removal. Their effects on a food web are predictable in kind: they outcompete natives for food or space, prey on species that have no defense against them, alter habitat structure, or bring disease.
Ohio's invaders. Zebra mussels arrived in the Great Lakes in the late 1980s in ships' ballast water. They filter plankton so efficiently that they clear the water, which starves the native plankton-eaters and pushes the energy of the lake down to the bottom, while their shells encrust intakes and native mussels. The emerald ash borer, a beetle from Asia detected in Ohio in the early 2000s, has killed a large share of the state's ash trees, changing forest canopy and the species that depended on ash. Garlic mustard and purple loosestrife crowd out native woodland and wetland plants and support far fewer insects. The round goby, another ballast-water fish, eats the eggs of native fish. Bighead and silver carp, escaped from southern fish farms, consume plankton at the base of the food web and have spread through the Mississippi and Ohio River systems toward the Great Lakes, including possible routes to Lake Erie; keeping them out is a major management effort. Each of these removes a link, adds a link, or shifts energy in the food web, and the consequences ripple: an invasive plant that replaces a native reduces the insects, which reduces the birds.
Should a species be introduced? Deliberate introduction sometimes helps: releasing a specialist insect from an invader's home range to feed on it (biological control), as with the leaf-feeding beetles released against purple loosestrife; stocking a fish to restore a fishery; moving individuals of an endangered species to a second site as insurance. The risks are that the introduced species attacks non-target natives, becomes invasive itself, or carries disease. The cane toad, released in Australia to eat crop beetles, ignored them and poisoned native predators. A sound assessment asks: is the agent specific to its target? Has it been tested on native species? Can its spread and host range be predicted? What happens if it fails? An agent that reproduces and establishes in the wild usually cannot be recalled or contained afterward, so the release is effectively permanent. The answers must come from experiments before release, not after.
A worked model in the prose: comparing two natural areas. Suppose a hypothetical breeding-bird survey of two 10-hectare woodlots, each in a single morning, records: Woodlot North, 14 species with counts 6, 5, 5, 4, 4, 3, 3, 3, 2, 2, 2, 1, 1, 1 (total 42); Woodlot South, 8 species with counts 20, 8, 4, 3, 2, 2, 2, 1 (total 42), and South is heavily invaded by garlic mustard and bush honeysuckle. North has higher richness (14 versus 8) and a far more even distribution; in South nearly half the birds belong to one species. The interpretation is that North's more diverse plant community supports more kinds of insects and nest sites. What the survey cannot prove: that the invasive plants caused the difference, since the two woodlots may differ in age, size or surroundings; a fair test would compare plots before and after invasive removal. The relevance to management is that a more diverse community has more redundancy and, at the scale of a single patch, often resists invaders better, though the evidence on this is mixed across larger regions.
Removals and additions. Because energy flows up from producers, removing a producer or a primary consumer can starve the species above it that depend on it, unless they can switch to other food; adding too many herbivores can overgraze the producers and then crash; and because persistent toxins that are retained in tissue biomagnify, a top predator that is protected but still eats contaminated prey is not safe, which is why conservation plans for fish-eating birds address water contamination as well as habitat.
Worked recovery reading: Hypothetical counts of nesting pairs of a recovering raptor in one state: 1980, 4; 1990, 10; 2000, 50; 2010, 150; 2020, 400. Growth per decade: ×2.5, ×5, ×3, ×2.7. The population grew roughly exponentially for forty years, consistent with the removal of a limiting toxin followed by protection, and the slowing between the last two decades may be the beginning of a leveling as suitable nest sites fill. Management inference: whether a recovery goal has been met depends on the target set in the recovery plan, which these data do not give; the next question is whether habitat, not toxin, now limits the population, which nest-site surveys would answer. The figures are illustrative.
Worked invasive impact trace: Zebra mussels arrive in a hypothetical lake. Year 1: the mussels filter plankton; water clarity doubles. Year 3: native plankton-eating fish decline for lack of food; light reaching the bottom lets rooted plants spread; bottom-dwelling species increase. Year 5: native mussels, encrusted and outcompeted, nearly disappear; intake pipes need cleaning. The mussels redirect production from the open-water food web to the bottom, favoring some species and starving others. A management plan cannot remove the mussels from an open lake, so it aims at preventing spread: boat-cleaning rules and ballast regulations.
Worked introduction assessment: A hypothetical proposal to release a weevil to control an invasive thistle. Questions and evidence needed: host specificity (feeding trials on native thistles and related crops; if the weevil eats any of them, reject); establishment (will it survive the winter?); effectiveness (does it reduce seed production enough to matter?); reversibility (once released, it cannot be recalled); and monitoring (native plant surveys before and for years after release). Potential benefits if it passes: sustained suppression of the thistle and reduced herbicide use, neither of which is guaranteed, so effectiveness and non-target effects must be monitored for years after release. Recommendation format: approve only with the specificity data in hand, never on the argument that the thistle is bad.
Worked biodiversity comparison: For the two hypothetical woodlots, compute Simpson's index. North: Σ n(n − 1) = 30 + 20 + 20 + 12 + 12 + 6 + 6 + 6 + 2 + 2 + 2 + 0 + 0 + 0 = 118; N(N − 1) = 42 × 41 = 1,722; D = 1 − 118/1,722 ≈ 0.93. South: 380 + 56 + 12 + 6 + 2 + 2 + 2 + 0 = 460; D = 1 − 460/1,722 ≈ 0.73. North is more diverse by richness, evenness and index. The index summarizes one morning's sample; repeated surveys through the season would be needed before drawing a firm conclusion.
Representation task: Draw a food web for an Ohio woodland or lake (at least ten organisms), then redraw it after one named invasive species arrives, showing which links are added, weakened or lost, and write one sentence per change explaining the mechanism (competition, predation, habitat change or disease). Add a labeled arrow showing where a persistent toxin would biomagnify.
Safe investigation, invasive plant survey: With permission, lay a 20 m tape (a transect) through a wooded or field edge near your school. Wear gloves, long sleeves and long pants (multiflora rose is thorny), learn to recognize and avoid poison ivy before you start, and check for ticks afterward. At every 2 m mark, place a 0.5 m × 0.5 m frame and count the stems of each plant type inside, using a field guide to identify any of garlic mustard, bush honeysuckle, multiflora rose or purple loosestrife. Record the percentage of quadrats in which each invasive occurs and the number of native types per quadrat. Repeat on a second transect in a less disturbed area. Result that supports the claim: quadrats with more invasive stems hold fewer native types. What it cannot show: cause, since disturbance may drive both; animal use of the plants; or change over time without a repeat survey. Do not pull plants unless your teacher directs it and the landowner agrees.
Independent performance: Write a plan (at least 250 words) to conserve a specific Ohio wilderness area, wetland or waterway that you research, or a hypothetical one you describe in detail. Success criteria: it names the ecosystem's key producers, primary consumers and top predators and one relationship among them; it identifies at least three threats, including one human impact and one invasive species, with the mechanism of harm for each; it proposes management actions matched to each threat, including one monitoring measurement with the value that would trigger action; it evaluates one proposed species introduction with the questions from the lesson; it explains, using biomagnification, why a predator at the top of the food web needs water-quality protection as well as habitat protection; and it marks every number as measured, sourced or hypothetical.
An adult may read the prompts aloud. Answer independently with words, objects, drawings or a demonstration before opening the answer guide. Award 1 point for a correct result or claim and 1 point for a matching explanation or demonstration; where a question asks only for a result (a corrected sentence, a spelling, a count), a fully correct result earns both points, and the answer guide shows what a complete response contains. Record prompting separately. The total (two points per question) is local practice feedback, not an Ohio proficiency level.
Distinguish an introduced species from an invasive species and give an example of each that is found in Ohio.
An introduced species is one humans moved beyond its natural range; an invasive species is an introduced species that spreads aggressively and causes ecological or economic harm. The ring-necked pheasant is introduced but not considered invasive; the zebra mussel is invasive.
Explain why an invasive species often thrives in its new range when it was kept in check at home.
In its native range its numbers are limited by predators, parasites, diseases and competitors that evolved alongside it. Those are often left behind when it is moved, and native species in the new range may lack defenses against it, so it faces fewer density-dependent controls and can spread rapidly, especially in disturbed habitats.
Describe how zebra mussels shift energy from the open-water food web of a lake to the bottom.
They filter plankton from the open water, starving native plankton-eating fish, while clearer water lets light reach the bottom, where rooted plants and bottom-dwelling species increase. Energy is shifted from the open-water food web to the bottom rather than lost, favoring some species and eliminating others.
Using the bald eagle, explain why identifying the mechanism of decline mattered more to recovery than protecting the birds alone.
The decline was caused by DDT biomagnifying through fish to the eagles and thinning their eggshells, so protected adults still failed to reproduce. Only banning the pesticide removed the cause; combined with nest and habitat protection, the population then recovered and the species was delisted in 2007.
List four questions that should be answered with evidence before a biological control species is introduced.
Is it specific to the target (feeding trials on native relatives and crops)? Has it been tested on native species? Can its spread and host range be predicted, given that an established agent usually cannot be recalled? What happens if it fails? Other defensible questions earn credit, such as whether it can survive the local climate and whether it reduces the target enough to matter. Monitoring before and after release should also be planned.
Two woodlots each hold 42 birds. North has 14 species with counts 6, 5, 5, 4, 4, 3, 3, 3, 2, 2, 2, 1, 1, 1; South has 8 species with counts 20, 8, 4, 3, 2, 2, 2, 1. Which is more biodiverse and how does that relate to resisting invasive species?
North, by richness (14 versus 8), evenness and Simpson's index: North Σ n(n − 1) = 118, D = 1 − 118/1,722 ≈ 0.93; South Σ n(n − 1) = 460, D = 1 − 460/1,722 ≈ 0.73. A community with more species has more redundancy in each role and fewer open niches, so it often resists and recovers from an invader better (the evidence is mixed at large scales); the survey alone, however, does not prove the invasive plants caused the second woodlot's lower diversity.
Explain what happens to a food web if a producer is removed and if too many consumers are introduced, and why a protected top predator can still be at risk.
Removing a producer can starve the primary consumers that depend on it, and the species above them, unless they can switch to other producers, because energy enters only through producers. Introducing too many herbivores can overgraze the producers and then the herbivores crash. A protected top predator can still be harmed because persistent toxins biomagnify up the chain to it, so its conservation requires controlling contaminants in the water as well as protecting habitat.