One of my favorite ecology intro activities is biotic and abiotic factors on the sidewalk.  Ask your students to go find examples of each, then bring them back to the sidewalk for discussion.  Kids love getting outside and it provides a great opportunity for discussion. 

This activity is included in my Ecology Lesson 1 with editable Google Apps and printable activities.

Testing paper towels is a great way to engage your students and have them experience science.  Towels are cheap and easy to use.  Measure how much water they can pick up, how fast it absorbs water or measure its strength.  Data is easily portrayed in a graph.  In the end, students can make recommendations based on their results.  In this picture below, we are trying to determine the number of drops a paper towel can hold. 

Looking for an easy way to plan this lab, check out my resource to learn more. Click Here. 

Studying invasive species is a great opportunity in science class.  Many of the organisms plague our ecosystems and out-compete native plants and animals.  In this lesson I asked my students to take a clipping of Japanese Knotweed and bring it back to the lab to study this fast growing invasive.  Here's a few things you can do.
1.  Take scientific pictures, include rulers for scale
2.  Study the roots, stems and leaves of these organisms.
3.  Grow sample plant (contained in the classroom)
4.  Research effective uses.  Many of my students found recipes for invasive edible plant species.
5.  Talk to kids about safe ways to control and destroy these plants. 

From the teaching side, just be sure you understand how to dispose of these organisms.  In our case we need to dry them and bag the plants before disposal to prevent the spread.  Also research your states noxious weed list to be sure there is no specific law governing the organisms you are working with. 

Using rubber bands and masses to learn about science.  In this lesson we had students use different masses to measure how much rubber bands stretched.  We culminated this activity a simulated bungee jumping activity.  Students used their data collected from lab to create the "best" simulated jump.