The Species Killers Part 2: An Introduction to Invasives
Intro to Invasives • “Invasive species (or invasives) are plants, animals, fungi, or microorganisms that spread rapidly and cause harm to other species” – Cornell Univ • Most are brought in from other continents willingly or unwillingly. • However, some invasive species can be native to an area. • E.g. some biologists consider Whitetail deer to be invasive due to their overly high population and the demands of this population level, which may be lowering the populations of other species (esp. forest understory) • Invasive species displace native species and prevent them from being able to obtain nutrition, reproduce, and perform natural functions at a normal rate.
Many names, same thing • Invasives can go by many other names, including • Introduced species • Nonindigenous Species • Alien species • Exotic species • Weeds • Pests • Some of these are correct for only some invasives • For example, Whitetail deer are native and not alien or exotic • Mosquitoes are pests but are not invasive
Clarification • Often “invasive” and “introduced” are used interchangeably • While this is often true, it is not always true • Some introduced species can be very helpful or valuable. • 98% of the US food supply comes from introduced plants and animals including… • Wheat • Rice • Cattle • Poultry • In a nutshell, a species is invasive if it displaces native species, spreads rapidly, and causes ecological harm.
Clarification 2 • There is also a misconception that all introduced species become invasive. • In fact, most do not. • Of every 100 exotic species introduced to North America, only about 10 are able to survive without the planting or assistance of humans • E.g. corn does not spread from its field on its own • Of the 10 in 100 that can survive without humans, only about 1 of these will cause serious ecological problems. • So odds are that only 1% of introduced species become invasive
However… • However, this 1% more than makes up for its minority status. • Environmental damage from invasive species is estimated at $138 billion per year. • To give some perspective, this is more than twice the total value of Wisconsin’s agricultural industry • Zebra mussels alone have caused $3 billion in damage to the Great Lakes. • This equates to nearly $100/yr lost for every man, woman, and child that live in a Great Lakes State because of one species! • NOAA: 35 million population; Cornell: $3 billion cost.
So how do they do it? • So why is it that one bug from Asia could destroy entire forests? • Why don’t we see this with most native species? • After all, all trees have predators of some kind? • Where do all these bugs come from? • If the Asian longhorned beetle and the Emerald Ash Borer came in on only a few shipments of lumber, how could enough offspring develop from these few individuals to destroy entire ecosystems? • How is it that these organisms can spread so quickly and so efficiently? • Why don’t native organisms usually do this? • TPS and Whiteboards
Successful Invaders • Invasive species usually have several of the following characteristics: • They grow rapidly and compete with other plants or animals • They produce large numbers of seeds/offspring at a young age • Their seeds/eggs can survive a long time before sprouting • They can travel long distances • They have few if any predators • Their native region has a climate similar to the affected area of the US • They have multiple reproductive strategies.
Factors Controlling Distribution • Distributionrefers to where a species is located. • Three factors control the distribution of a species. They are • 1. Colonization • 2. Resources and suitable habitat • 3. Interactions with other organisms • Competition • Predation • Herbivory
1. Colonization • Colonization refers to a species’ first arrival in a new area. • How a colonizes a new area can tell us if and how it will spread • E.g. zebra mussels first entered North America in the Great Lakes and spread from there. • The adaptations of a species are important in its ability to colonize new sites. • The zebra mussel’s adaptations were well suited for any of the Great Lakes, and it began to spread. • If a species can get a foothold in an area, it can spread from there and increase its distribution. • Without colonization, there is no distribution.
Spread of the Zebra Mussel, 1998-2008http://fl.biology.usgs.gov/Nonindigenous_Species/ZM_Progression/zm_progression.html
2. Resources and Suitable Habitat • The spread and distribution of a species is also controlled by availability of resources and suitable habitat • Each species has particular needs for resources • E.g. plants need proper levels of light, water, nutrients, etc • Again, a habitat is the type of environment in which a species occurs and includes both physical and biological characteristics. • Invasive species are often “habitat generalists” • They can occupy a broad range of habitats • Because they can adapt to many kinds of habitats, they can spread to many parts of the country. • Invasives have broad distributions because they don’t have specific needs…and many kinds of habitat can fill those needs.
3. Interactions with other organisms • Living things are in constant exposure and interaction with other living things • Because resources are limited, and because our genes allow us to reproduce without limit, there is constant competition for available resources. • A species that is able to use resources to grow and reproduce faster than other species is a superior competitor.
Invasives Compete Well • Invasive species are excellent competitors • They can obtain resources more quickly or efficiently than the native species in a habitat • As such, the native species have lowered reproduction and continuously lose their status in an ecosystem. • If unchecked, invasive species have the potential to eradicate some or all native species and hamper or destroy ecological processes.
The biological invasion curve showing that detection and prevention make the most sense from monetary, environmental and effectiveness perspectives.
Sometimes Invasives Have Help (from us!) • Invasives very rarely occur unless they have help. • In every example in this presentation, the invasive species was introduced because human transportation. • They hitchhiked with humans • Humans can aid the spread of invasives in many ways. Two key ways humans aid invasives are… • Transportation • Habitat Disturbances
Habitat Succession and Disturbance • Transporting invasives allows them to gain access to ecosystems they were a never a part of. • Without transportation, invasives would never leave their native regions. • Besides transporting invasive species, humans can also aid them through habitat disturbance. • We briefly discussed habitat succession, or the gradual change of habitat over time (such as fields taken over by shrubs, to later become a forest). • Habitat disturbancesare when habitats experience an event that changes the availability of resources such as light or nitrogen.
Habitat Distubrances • Habitat Disturbances can be natural • For example, a fire, flood, or volcano is a natural occurrence that can completely change a habitat • Habitat Disturbances can also be manmade • Building roads, agriculture, pollution, invasives, and many other components of human activity affect the availability of resources in a habitat. • Again, a community is the animals and plants that occur in an ecosystem • Humans cause many disturbances to habitats. • These disturbances can aid invasive species.
Examples of Human Habitat Distubances • When humans build roads, roadsides are first disturbed by the construction equipment that makes the road. • Later, disturbances occur from the repeated mowing and spraying of herbicides • Because of these ongoing disruptions, the process of Succession is disrupted. • For example, along the roadside, only grasses are able to survive; any shrubs or trees will never gain a foothold. • These disturbances can also aid invasive plants and animals. • Often , invasive plants and weeds need disturbed soil in order to gain a foothold and be able to compete against native species.
Invasives as a form of pollution • We typically think of pollution as something from factories causing lowered air or water quality • This would be chemical pollution • Ecologists often use the term biological pollutionto label the harm caused by invasive species • While chemical pollution can often be cleaned, or at least have a lowered impact over time, biological pollution is far different. • This is because biological pollution can reproduce on its own and continue to grow long after the first environmental assault.