Lecture 17: Exotic and invasive species

introduced vs exotic species

• exotic species are not native to an area

• “exotic species: often used interchangeably with introduced species, but some native species can be reintroduced to parts of their previous range

• introductions of exotic species may be intentional or inadvert

Burmese python in southern florida

• native to southeast asia

  • popular in North American exotic pet trade

• introduced to florida everglades by:

  • release of individuals too large for owners to care for

  • escaped pet animals

  • destruction of breeding facility by hurricane in 1992

impacts of introduced exotic species

• ruddy duck and white-headed duck

• beyond consumptive effects like case of Burmese python in florida, introduced species can have wide range of impacts on local fauna

• example: ruddy duck

  • Eurasia has similar species (white-headed duck) - IUCN threatened species

  • Ruddy duck introduced to Europe in late 1940s; subsequent population increases and range expansion in EU

  • competes with white-headed duck; also able to hybridize with white-headed duck (loss and potential extirpation from restricted ranges around Mediterranean)

  • in response, western EU countries implemented culling (primarily through selective hunting)

invasive species

• invasive species: exotic species that spread rapidly in new area

  • or invasive species are exotic species that have harmful environmental impacts, esp. on native species

• ecologists tend to confuse first definition (interchangeable use implies correlation between how quickly an organism spreads and the damage to environment it causes); assume becuase species spreads fast, it causes harm

do faster-spreading invasives cause larger impacts

• tested whether invasive species (defined in terms of establishment and spreading rate) are more likely to reduce native species populations

• quantified relationship between rate of establishment or spread and impact rank in naive species; for ~70 species

• No relationship between spread rate and impact; also pooled impact ranks into low and high and compared rate of spread (<3 = low; >4 = high)

• no discernable pattern when split by taxa

• author conclusions: term invasive should not be used to connote particulate species that threaten biodiversity

North American Swans

• populations of feral mute swans in NA have been growing at very fast rate

• i.e. Chesapeake Bay (Maryland and Virginia) populations have grown from 1962 (5 birds released) to over 4000 by 2001

• 9.1% increase per-year in US atlantic Flyway

• mute swan effects:

  1. displace native species

  2. attack and kill native species

  3. hybridize with trumpeter swans (reduce genetic stock)

  4. consume and uproot aquatic vegetation; non-migratory do not field feed (heavy competition for resources)

Mute swans on the great lakes

• more locally, large population increases seen around Great lakes

• combined aerial survey data, midwinter waterfowl inventory data, Christmas bird count data to estimate rates of increase

  • quick increase in population size of 10-21%/year; 30,000 swans in lower great lakes region

  • we can ask: What is carrying capacity for swans on lower great lakes?

• accelerating growth phase - how can we determine K? (K = CARRYING CAPACITY)

  • can be determined with a graph; where population asymptotes, or birth = death

  • OR

  • what habitat do swans need

  • how much habitat is available

  • what density of birds can the habitat support

POPULATION control of mute swans

• Population control began in 2001

• manage by egg addling or direct killing of adults

• addling: involves coating eggs with oil to prevent them from hatching; by returning eggs to nest, the bird will not attempt to re-lay

• criticism of population control of mute swans:

  • destroying eggs is cruel, they say

  • despite being more gentle form of management, still criticized

global distribution of wild pigs

• wild pigs have largest global range of any non-domesticated terrestrial mammal on earth

• native to Eurasia; introduced to Americas and Oceania in recent history

• highly damaging species, esp. to regions with few native mammal species (polynesia, Aus.); 0.5% taxa threatened in NA

• wild pigs threaten 672 taxa in 54 different countries

• most taxa are listed as critically endangered or endangered (mostly plants)

• 14 species have been driven to extinction as result of impacts from wild pigs

• omnivorous opportunistic feeders: will predate small animals

• root extensively in search of food; disrupt soil structure, cause erosion, damage vegetation, lead to habitat degradation

• disease transmission

• outcompete native WL for resources such as food and habitat

• very high reproductive rates

North America’s wild pigs: Canadian population

• originally brought from Europe to Canada 3 decades ago and mated to domestic pigs to produce a marketable hybrid (did not work well)

• NDMNRF has found evidence that ~14 pigs in a sounder spotted in pickering ONt. this month

• wild pigs detected across southern canada

North America’s wild pigs: USA population

• feral swine population has increased a lot since 1982 - 2020

• mostly south-eastern states

• economic damage in addition to ecological damage

• crop loss estimates: $61 million corn

controlling wild pig populations

• fencing:

  • stay install fencing to exclude feral swans from crops

  • electric fencing is effective in some cases but may be cost prohibitive for large areas

  • traditional fencing + habitat modification (cleaning underbrush along fence line) can be effective

  • feral swine are clever so may destroy fences if motivated or agitated (should be considered during construction)

• harassment:

  • can be effective for immediately removing from area

  • not practical on large scale (likely shift feral swine problems from one area to another)

  • also makes them wary and can reduce success rates of other control methods

• vaccination of livestock and pets:

  • keep livestock vaccinated and parasite free and in good condition to aid disease resistance

  • diseases from swine that may be transferred to livestock: leptospirosis, brucellosis, porcine reproductive and respiratory syndrome, porcine circovirus T2, influenza, E. coli

• trapping:

  • captured swine should not be moved or released to environment; humanely euthanize once in trap

  • intelligent so if trap is not set up properly or not pre-baited, individuals not captured will be educated and much more difficult to capture later on

• snares:

  • can be useful alongside traps or in terrain where traps are impractical and only few individuals remian

• ground shooting:

  • effective only when few individuals are present in the area; if larger groups are observed, shooting few individuals can disrupt social organization and make them spread further across landscape

  • labor intensive and unlikely to give desired relief from damage

• aerial operations:

  • if landscape is open (grassland) then effective means of quickly and efficiently reducing feral swine numbers

  • not permitted in regions and may be cost-prohibitive

• toxicants:

  • potential to be cost-effective tool for reducing populations

  • currently working on toxicant capable of effectively and humanely removing feral swine without having adverse effect on environment and non-target species

  • NO TOXICANT CURRENTLY REGISTERED FOR USE ON FERAL SWINE IN USA

Wild pig control programs in Canada

• Alberta - whole Sounder trapping incentive program

  • encourages the elimination of entire Sounders (social groups)

  • $75 per set of ears per sounder

  • from April 1 2022 to march 31 2024

• program concluded without any submissions

• Saskatchewan - Feral wild boar control program

  • corrals set up in high traffic areas and grain placed as bait inside corral enclosure

  • trail cams used to monitor pig movements

  • when trap operators are confident that all members are inside corral, gate is triggered and pigs trapped inside

  • boars then euthanized

• little evidence of wild boar in Ontario - mainly feral domestic animals

  • if seen, then report [e-mail], call, or inaturalist Ontario wild pig reporting