Analysis: Change over time

How are invasive species changing over time?

Watch the milfoil video!
Watch the crab video!
Use the How-To Guide>>

Use the map to see how invasives in freshwater, coastal, and upland ecosystems are expanding and moving from one year to the next. Since VS is so new, you’ll have the most success right now using one of these historical datasets:


  • Freshwater: Variable watermilfoil
  • Upland: Hemlock woolly adelgid
  • Coastal: Codium
  • Coastal: Asian shore crab

Mission Analysis Steps

1. Launch the MAP
2. Click the "Change Search" button"

  • Select a species from the "Search by Species" pulldown
  • Show “ID confirmed by expert”
  • Select an initial date range:
    • Variable watermilfoil:
    • FROM 01/01/1996 TO 12/31/1998

    • Codium:
    • FROM 01/01/2008 TO 12/31/2008

    • Hemlock woolly adelgid:
    • analysis_changetime_date.jpg


    • Asian shore crab:
    • FROM 01/01/2004 TO 12/31/2004

  • Click "Map it"

3. Check out the map, and note where the species is found and not found

4. Click "Change Search" button to change the date range again:

  • Keep FROM the same, change TO by 1 year or more
    • Variable watermilfoil: TO 12/31/2000
    • Codium: TO 12/31/2009
    • Hemlock woolly adelgid: COMING SOON
    • Asian shore crab: TO 12/31/2005

5. Toggle back and forth between the maps and note the changes over time

6. Click "Change Search" button to change the date range again:

  • Like in STEP 4, keep FROM the same, change TO by 1 year or more
  • Do this as many times as you need to to reach 2011

What Does It Mean?

Now it's time to look at the change you saw on the map, and think about why that change might be happening. You might also have expected to see a different kind of change happen than the data show, and want to figure out why that change didn't happen. Check out Elizabeth Stephenson's video to hear how she made sense of the Asian shore crab data she collected.

1. What’s the most important change you see from one date range to the next?

2. Why do you think this change is happening?

  • Do you think it’s because more people are looking for the species?
  • Do you think the species is moving and expanding its population?
  • How is this movement and expansion happening?

3. What do you imagine the map will look like 5 years from now? 20 years from now? What’s your prediction?


Share What You Learned

1. Do Projects! Make a change over time movie, post to the VS blog, shoot a PSA, more!

2. Create your own Field Mission to get the VS community collecting data to test out YOUR prediction!